[Federal Register Volume 61, Number 43 (Monday, March 4, 1996)]
[Proposed Rules]
[Pages 8328-8370]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-3554]




[[Page 8327]]

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Part II





Department of Transportation





_______________________________________________________________________



Research and Special Programs Administration



_______________________________________________________________________



49 CFR Parts 171, 173, and 178



Restructuring of Cylinder Specifications Requirements; Proposed Rule

  Federal Register / Vol. 61, No. 43 / Monday, March 4, 1996 / Proposed 
Rules   

[[Page 8328]]


DEPARTMENT OF TRANSPORTATION

Research and Special Programs Administration

49 CFR Parts 171, 173, and 178

[Docket HM-220B; Notice No. 96-2]
RIN 2137-AC81


Restructuring of Cylinder Specifications Requirements

AGENCY: Research and Special Programs Administration (RSPA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

SUMMARY: RSPA is proposing to revise the Hazardous Materials 
Regulations (HMR) by restructuring the cylinder specification 
requirements. The intended effect of this rulemaking is to reduce the 
size of the HMR through consolidation of repetitive requirements and 
other formatting changes. This action will eliminate pages of 
regulations without substantially changing the regulatory requirements 
or affecting safety. It is in response to President Clinton's March 4, 
1995 Regulatory Reinvention Initiative memorandum to heads of 
departments and agencies calling for a review of all agency 
regulations. RSPA is also proposing to make corresponding reference 
changes throughout the HMR.

DATES: Comments must be received on or before April 26, 1996.

ADDRESSES: Please address written comments to the Dockets Unit (DHM-
30), Research and Special Programs Administration, U.S. Department of 
Transportation, 400 7th Street, SW., Washington, DC 20590-0001. 
Comments may also be faxed to (202) 366-3753. Comments should identify 
the docket (Docket No. HM-220B). The Dockets Unit is located in Room 
8421 of the Nassif Building, 400 Seventh Street SW., Washington, DC 
20590-0001. Office hours are 8:30 a.m. to 5:00 p.m., Monday through 
Friday, except on public holidays when the office is closed.

FOR FURTHER INFORMATION CONTACT: John A. Gale, (202) 366-8553; Office 
of Hazardous Materials Standards, RSPA, Department of Transportation, 
Washington, DC 20590-0001.

SUPPLEMENTARY INFORMATION:

I. Background

    On March 4, 1995, President Clinton issued a Regulatory Reinvention 
Initiative memorandum to heads of departments and agencies calling for 
a review of all agency regulations and elimination or revision of those 
regulations that are outdated or in need of reform. RSPA has performed 
an extensive review of the Hazardous Materials Regulations (HMR; 49 CFR 
Parts 171-180) and associated procedural rules (49 CFR Parts 106 and 
107) in response to the President's directive.
    The President also directed that front line regulators ``* * * get 
out of Washington and create grassroots partnerships'' with people 
affected by agency regulations. On April 4, 1995, RSPA published in the 
Federal Register (60 FR 17049) a Notice of Public Meetings and request 
for comment on its hazardous materials safety program. Comments were 
requested on ways to improve the HMR and the kind and quality of 
services its customers want. RSPA held seven public meetings and 
received over 50 comments in response to the notice. On July 28, 1995, 
RSPA published a second Notice of Public Meetings in the Federal 
Register (60 FR 38888) which announced five more public meetings that 
were held from September through January 1996.
    One area identified by RSPA in its review of the HMR was the need 
to reform the cylinder specifications in 49 CFR Part 178. RSPA 
estimates that by consolidating duplicative requirements in 23 cylinder 
specifications, that it will eliminate at least 40 pages from the CFR. 
By reformatting the specifications, RSPA proposes to eliminate over 450 
sections from Part 178 of Title 49. The combined effect of these 
changes will be to make the regulations shorter and easier to use and 
help RSPA move toward a goal of being able to issue the HMR in one 
volume of the Code of Federal Regulations, rather than two.
    This rulemaking also serves as the model for a more comprehensive 
rulemaking, being developed by RSPA in cooperation with the Compressed 
Gas Association, for which a notice of proposed rulemaking is 
anticipated later this year. In this latter rulemaking, under Docket 
HM-220, RSPA intends to propose substantive changes to the cylinder 
specifications to accommodate contemporary manufacturing techniques, 
eliminate obsolete requirements, contemporize regulatory language and 
make safety enhancements to the regulations.

II. Proposed Changes

    In this NPRM, RSPA is proposing to revise the HMR by restructuring 
the cylinder specification requirements in 49 CFR Part 178. The 
proposed restructuring of the cylinder specifications would: (1) 
consolidate similar sections; (2) reformat subpart C of Part 178 for 
consistency with the format of the rest of Part 178; and (3) revise 
section references throughout the HMR to correspond to the revised 
sections. RSPA intends to streamline the cylinder specification 
requirements without making substantive changes to them.
    Sections that have been identified by RSPA for consolidation are 
the sections of each specification addressing compliance, authorized 
inspectors, duties of the inspector, the inspector's report, record 
retention, defects, safety relief devices, and marking. These sections 
will be consolidated into a new Sec. 178.35. Proposed Sec. 178.35, 
entitled ``General requirements for all DOT specification cylinders'' 
will prescribe these general requirements for all DOT specification 
cylinders. However, because some of the duties of the inspector and 
marking requirements are specific to the individual cylinder design, 
some specifications would have additional marking and inspector 
requirements remaining in their sections.
    For the inspector's report, RSPA has proposed to adopt the 
inspector report formats in Compressed Gas Association (CGA) Pamphlet 
C-11, ``Recommended Practices for Inspection of Compressed Gas 
Cylinders at Time of Manufacture.'' The report formats can be modified 
to represent the inspection of specific cylinders. Additional 
information may be required as stated in each specification.
    Those sections remaining in each specification will be consolidated 
into a single section. Presently, each specification is set forth in 
approximately 22 different sections. Under this proposal, there would 
be only one section for each specification. For example, Specification 
3B is currently set forth in 24 sections, Secs. 178.38 through 178.38-
23. In this NPRM, Specification 3B is set forth in one section, 
Sec. 178.38. Some of the requirements are relocated in Sec. 178.35. 
Sixteen of the old sections are converted to paragraphs (a) through (o) 
of Sec. 178.38. As an aid to the reader, the regulatory text in this 
notice includes all of the requirements for cylinders in the current 
Subpart C of part 178, even though not all of the requirements are 
changed.
    The purpose of this rulemaking action is to reduce the size of the 
HMR and make it easier to use. It is not intended to make substantive 
changes to regulatory requirements and no adverse impacts are 
anticipated on the regulated community. 

[[Page 8329]]


III. Regulatory Analyses and Notices

Executive Order 12866 and DOT Regulatory Policies and Procedures

    This proposed rule is not considered a significant regulatory 
action under section 3(f) of Executive Order 12866 and was not reviewed 
by the Office of Management and Budget. The rule is not considered 
significant under the regulatory policies and procedures of the 
Department of Transportation (44 FR 11034). The economic impact of this 
rule is minimal to the extent that the preparation of a regulatory 
evaluation is not warranted.

Executive Order 12612

    This proposed rule has been analyzed in accordance with the 
principles and criteria contained in Executive Order 12612 
(``Federalism''). The Federal hazardous materials transportation law 
(49 U.S.C. 5101-5127) contains an express preemption provision that 
preempts State, local, and Indian tribe requirements on certain covered 
subjects. Covered subjects are:
    (i) the designation, description, and classification of hazardous 
material;
    (ii) the packing, repacking, handling, labeling, marking, and 
placarding of hazardous material;
    (iii) the preparation, execution, and use of shipping documents 
pertaining to hazardous material and requirements respecting the 
number, content, and placement of such documents;
    (iv) the written notification, recording, and reporting of the 
unintentional release in transportation of hazardous material; or
    (v) the design, manufacturing, fabrication, marking, maintenance, 
reconditioning, repairing, or testing of a package or container which 
is represented, marked, certified, or sold as qualified for use in the 
transportation of hazardous material.
    The Federal hazardous materials transportation law provides that if 
DOT issues a regulation concerning any of the covered subjects after 
November 16, 1990, DOT must determine and publish in the Federal 
Register the effective date of Federal preemption. 49 U.S.C. 
5125(b)(2). That effective date may not be earlier than the 90th day 
following the date of issuance of the final rule and not later than two 
years after the date of issuance. This proposed rule deals with the 
packaging of compressed gases. Although this proposal does not 
contemplate substantive changes, RSPA solicits comments on whether the 
proposed rule would have any effect on State, local or Indian tribe 
requirements and, if so, the most appropriate effective date of Federal 
preemption. Because RSPA lacks discretion in this area, preparation of 
a federalism assessment is not warranted.

Regulatory Flexibility Act

    I certify that this proposed rule will not have a significant 
economic impact on a substantial number of small entities. This 
proposed rule does not impose any new requirements on persons subject 
to the HMR.

Paperwork Reduction Act

    This proposed rule does not propose any new information collection 
requirements.

Regulation Identifier Number (RIN)

    A regulation identifier number (RIN) is assigned to each regulatory 
action listed in the Unified Agenda of Federal Regulations. The 
Regulatory Information Service Center publishes the Unified Agenda in 
April and October of each year. The RIN number contained in the heading 
of this document can be used to cross-reference this action with the 
Unified Agenda.

List of Subjects

49 CFR Part 171

    Exports, Hazardous materials transportation, Hazardous waste, 
Imports, Reporting and recordkeeping requirements.

49 CFR Part 173

    Hazardous materials transportation, Packaging and containers, 
Radioactive materials, Reporting and recordkeeping requirements, 
Uranium.

49 CFR Part 178

    Hazardous materials transportation, Packaging and containers, 
Reporting and recordkeeping requirements.

    In consideration of the foregoing, 49 CFR parts 171, 173, and 178 
would be amended to read as follows:

PART 171--GENERAL INFORMATION, REGULATIONS, AND DEFINITIONS

    1. The authority citation for Part 171 would continue to read as 
follows:

    Authority: 49 U.S.C. 5101-5127; 49 CFR part 1.53.

    2. In Sec. 171.7(a)(3), in the table, under the entry ``Aluminum 
Standards and Data, Seventh Edition, June 1982'', the section reference 
``178.65-5'' is revised to read ``178.65''; and under the entry 
Compressed Gas Association, Inc., a new entry is added in alpha-
numerical order to read as follows:


Sec. 171.7  Reference material.

* * * * *
    (a) * * *
    (3) * * *

------------------------------------------------------------------------
                                                                49 CFR  
                 Source and name of material                   reference
------------------------------------------------------------------------
                                                                        
                  *        *        *        *        *                 
                                                                        
              Compressed Gas Association, Inc.,                         
                                                                        
                  *        *        *        *        *                 
CGA Pamphlet C-11, Recommended Practices for Inspection of              
 Compressed Gas Cylinders at Time of Manufacture, 1993......      178.35
                                                                        
                  *        *        *        *        *                 
------------------------------------------------------------------------

* * * * *

PART 173--SHIPPERS--GENERAL REQUIREMENTS FOR SHIPMENTS AND 
PACKAGINGS

    3. The authority citation for Part 173 would continue to read as 
follows:

    Authority: 49 U.S.C. 5101-5127; 49 CFR part 1.53.


Sec. 173.34  [Amended]

    4. In Sec. 173.34, paragraph (h) would be amended by:
    a. Removing, in the first sentence, the phrase ``Secs. 178.36-9(a), 
178.37-9(a), 178.38-9(a), and 178.40-9(a)'' and replacing it with the 
phrase ``Secs. 178.36(e), 178.37(e), 178.38(e), and 178.40(e)''.
    b. Removing, in the fourth sentence, the phrase ``Sec. 178.36-9(a), 
Sec. 178.37-9(a), Sec. 178.38-9(a), or Sec. 178.40-9(a)'' and replacing 
it with the phrase ``Sec. 178.36(e), Sec. 178.37(e), Sec. 178.38(e), or 
Sec. 178.40(e)''.


Sec. 173.316  [Amended]

    5. In Sec. 173.316, in paragraph (a)(8), the section reference 
``178.57- 20(a)(4)'' would be revised to read ``178.35'' and in 
paragraph (c)(3)(ii) the section reference ``178.57-20'' would be 
revised to read ``178.35''.

PART 178--SPECIFICATIONS FOR PACKAGINGS

    6. The authority citation for Part 178 would continue to read as 
follows:

    Authority: 49 U.S.C. 5101-5127; 49 CFR 1.53.

    7. Subpart C of Part 178 would be revised to read as follows:

Subpart C--Specifications for Cylinders

Sec.
178.35  General requirements for specification cylinders.
178.36  Specifications 3A and 3AX seamless steel cylinders.
178.37  Specification 3AA and 3AAX seamless steel cylinders. 

[[Page 8330]]

178.38  Specification 3B seamless steel cylinders.
178.39  Specification 3BN seamless nickel cylinders.
178.42  Specification 3E seamless steel cylinders.
178.44  Specification 3HT seamless steel cylinders for aircraft use.
178.45  Specification 3T seamless steel cylinder.
178.46  Specification 3AL seamless aluminum cylinders.
178.47  Specification 4DS welded stainless steel cylinders for 
aircraft use.
178.50  Specification 4B welded or brazed steel cylinders.
178.51  Specification 4BA welded or brazed steel cylinders.
178.53  Specification 4D welded steel cylinders for aircraft use.
178.55  Specification 4B240ET welded or brazed cylinders.
178.56  Specification 4AA480 welded steel cylinders.
178.57  Specification 4L welded insulated cylinders.
178.58  Specification 4DA welded steel cylinders for aircraft use.
178.59  Specification 8 steel cylinders with porous fillings for 
acetylene.
178.60  Specification 8AL steel cylinders with porous fillings for 
acetylene.
178.61  Specification 4BW welded steel cylinders with electric-arc 
welded longitudinal seam.
178.65  Specification 39 non-reusable (non-refillable) cylinders.
178.68  Specification 4E welded aluminum cylinders.

Subpart C--Specifications for Cylinders


Sec. 178.35  General requirements for specification cylinders.

    (a) Compliance with the requirements of this subpart is required in 
all details.
    (b) Inspections and analyses. Chemical analyses and tests as 
specified must be made within the United States unless otherwise 
approved in writing by the Associate Administrator, in accordance with 
Sec. 173.300b of this subchapter. Inspections and verifications must be 
performed by--
    (1) An independent inspection agency approved in writing by the 
Associate Administrator, in accordance with Sec. 173.300a of this 
subchapter; or
    (2) For DOT Specifications 3B, 3BN, 4B, 4BA, 4D (water capacity 
less than 1,100 cubic inches), 4B240ET, 4AA480, 4L, 8, 8AL, 4BW, 39 
(marked service pressure 900 p.s.i.g. or lower) and 4E manufactured in 
the United States, a competent inspector of the manufacturer.
    (c) Duties of inspector. The inspector shall determine that each 
cylinder made is in conformance with the applicable specification. 
Except as otherwise specified in the applicable specification, the 
inspector shall perform the following:
    (1) Inspect all material and reject any not meeting applicable 
requirements. For cylinders made by the billet-piercing process, 
billets must be inspected and shown to be free from pipe, cracks, 
excessive segregation and other injurious defects after parting or, 
when applicable, after nick and cold break.
    (2) Verify the material of construction meets the requirements of 
the applicable specification by--
    (i) Making a chemical analysis of each heat of material;
    (ii) Obtaining a certified chemical analysis from the material 
manufacturer for each heat of material (a ladle analysis is 
acceptable); or
    (iii) If an analysis is not provided for each heat of material by 
the material manufacturer, by making a check analysis of a sample from 
each coil, sheet, or tube.
    (3) Verify compliance of cylinders with the applicable 
specification by--
    (i) Verifying identification of material is proper;
    (ii) Inspecting the inside of the cylinder before closing in ends;
    (iii) Verifying that the heat treatment is proper;
    (iv) Obtaining samples for all tests and check chemical analyses;
    (v) Witnessing all tests;
    (vi) Verify threads by gauge;
    (vii) Reporting volumetric capacity and tare weight (see report 
form) and minimum thickness of wall noted; and
    (viii) Verifying that each cylinder is marked in accordance with 
the applicable specification.
    (4) Furnish complete test reports required by this subpart to the 
maker of the cylinder and, upon request, to the purchaser. The test 
report must be retained by the inspector for fifteen years from the 
original test date of the cylinder.
    (d) Defects. A cylinder may not be constructed of material with 
seams, cracks, laminations, or other injurious defects.
    (e) Safety devices and protection for valves, safety devices, and 
other connections, if applied, must be as required or authorized by the 
appropriate specification, and as required in Secs. 173.34 and 173.301 
of this subchapter.
    (f) Markings. Markings on a DOT Specification cylinder must conform 
to applicable requirements.
    (1) Each cylinder must be marked with the following information:
    (i) The DOT specification marking must appear first, followed 
immediately by the service pressure. For example, DOT-3A1800.
    (ii) The serial number must be placed just below or immediately 
following the DOT specification marking.
    (iii) A symbol (letters) must be placed just below, immediately 
before or following the serial number. Other variations in sequence of 
markings are authorized only when necessitated by a lack of space. The 
symbol and numbers must be those of the manufacturer. The symbol must 
be registered with the Associate Administrator; duplications are not 
authorized.
    (iv) The inspector's official mark and date of test (such as 5-95 
for May 1995) must be placed near the serial number. This information 
must be placed so that dates of subsequent tests can be easily added. 
An example of the markings prescribed in this paragraph (f)(1) is as 
follows:

DOT-3A1800
1234
XY
AB 5-95

or;

DOT-3A1800-1234-XY
AB 5-95

where:

DOT-3A = specification number
1800 = service pressure
1234 = serial number
xy = symbol of manufacturer
AB = inspector's mark
5-95 = date of test

    (2) Additional required marking must be applied to the cylinder as 
follows:
    (i) The word ``spun'' or ``plug'' must be placed near the DOT 
specification marking when an end closure in the finished cylinder has 
been welded by the spinning process, or effected by plugging.
    (ii) As prescribed in specification 3HT (Sec. 178.44) or 3T 
(Sec. 178.45), if applicable.
    (3) Marking exceptions.
    (i) A DOT 3E cylinder is not required to be marked with the 
inspector mark.
    (ii) An identifying lot number may be marked on the cylinder in 
place of a serial number for cylinders not over 2 inches outside 
diameter or for cylinders with a volumetric capacity not exceeding 60 
cubic inches. Each lot shall not have over 500 cylinders.
    (4) Unless otherwise specified in the applicable specification, the 
markings on each cylinder must be stamped plainly and permanently on 
the shoulder, top head, or neck.
    (5) The size of each marking must be least 0.25 inch or as space 
permits.
    (6) Other markings are authorized provided they are made in low 
stress areas other than the side wall and are not of a size and depth 
that will create harmful stress concentrations. Such 

[[Page 8331]]
marks may not conflict with any DOT required markings.
    (g) Inspector's report. Each inspector shall prepare a report 
containing, at a minimum, the applicable information listed in CGA 
Pamphlet C-11. Any additional information or markings that are required 
by the applicable specification must be shown on the test report. The 
signature of the inspector on the reports certifies that the processes 
of manufacture and heat treatment of cylinders were observed and found 
satisfactory.
    (h) Report Retention. The manufacturer of the cylinders shall 
retain the reports required by this subpart for 15 years from the 
original test date of the cylinder.


Sec. 178.36  Specification 3A and 3AX seamless steel cylinders.

    (a) Type size and service pressure. In addition to the requirements 
of Sec. 178.35, cylinders must conform to the following:
    (1) A DOT-3A cylinder is a seamless steel cylinder with a water 
capacity (nominal) not over 1,000 pounds and a service pressure of at 
least 150 pounds per square inch.
    (2) A DOT-3AX is a seamless stainless steel cylinder with a water 
capacity not less than 1,000 pounds and a service pressure of at least 
500 pounds per square inch, conforming to the following requirements:
    (i) Assuming the cylinder is to be supported horizontally at its 
two ends only and to be uniformly loaded over its entire length 
consisting of the weight per unit of length of the straight cylindrical 
portion filled with water and compressed to the specified test 
pressure; the sum of two times the maximum tensile stress in the bottom 
fibers due to bending, plus that in the same fibers (longitudinal 
stress), due to hydrostatic test may not exceed 80 percent of the 
minimum yield strength of the steel at such maximum stress. Wall 
thickness must be increased when necessary to meet the requirement.
    (ii) To calculate the maximum longitudinal tensile stress due to 
bending, the following formula must be used:

S=Mc/I

    (iii) To calculate the maximum longitudinal tensile stress due to 
hydrostatic test pressure, the following formula must be used:

S=A1P/A2

where:

S = tensile stress-p.s.i.;
M = bending moment-inch pounds (wl\2\)/8;
w = weight per inch of cylinder filled with water;
l = length of cylinder-inches;
c = radius (D)/(2) of cylinder-inches;
I = moment of inertia-0.04909 (D\4\-d\4\) inches fourth;
D = outside diameter-inches;
d = inside diameter-inches;
A1 = internal area in cross section of cylinder-square inches;
A2 = area of metal in cross section of cylinder-square inches;
P = hydrostatic test pressure-p.s.i.

    (b) Steel. Open-hearth or electric steel of uniform quality must be 
used. Content percent may not exceed the following: Carbon, 0.55; 
phosphorous, 0.045; sulphur, 0.050.
    (c) Identification of material. Material must be identified by any 
suitable method, except that plates and billets for hot-drawn cylinders 
must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No fissure or other defect is 
permitted that is likely to weaken the finished cylinder appreciably. A 
reasonably smooth and uniform surface finish is required. If not 
originally free from such defects, the surface may be machined or 
otherwise treated to eliminate these defects. The thickness of the 
bottoms of cylinders welded or formed by spinning is, under no 
condition, to be less than two times the minimum wall thickness of the 
cylindrical shell; such bottom thicknesses must be measured within an 
area bounded by a line representing the points of contact between the 
cylinder and floor when the cylinder is in a vertical position.
    (e) Welding or brazing. Welding or brazing for any purpose 
whatsoever is prohibited except as follows:
    (1) Welding or brazing is authorized for the attachment of 
neckrings and footrings which are non-pressure parts and only to the 
tops and bottoms of cylinders having a service pressure of 500 pounds 
per square inch or less. Cylinders, neckrings, and footrings must be 
made of weldable steel, the carbon content of which may not exceed 0.25 
percent except in the case of 4130X steel which may be used with proper 
welding procedures.
    (2) As permitted in paragraph (d) of this section.
    (3) Cylinders used solely in anhydrous ammonia service may have a 
\1/2\ inch diameter bar welded within their concave bottoms.
    (f) Wall thickness. For cylinders with service pressure less than 
900 pounds, the wall stress may not exceed 24,000 pounds per square 
inch. A minimum wall thickness of 0.100 inch is required for any 
cylinder over 5 inches outside diameter. Wall stress calculation must 
be made by using the following formula:

S=[P(1.3D\2\+0.4d\2\)]/(D\2\-d\2\)

where:

S=wall stress in pounds per square inch;
P=minimum test pressure prescribed for water jacket test or 450 pounds 
per square inch whichever is the greater;
D=outside diameter in inches;
d=inside diameter in inches.

    (g) Heat treatment. The completed cylinder must be uniformly and 
properly heat-treated prior to tests.
    (h) Openings in cylinders and connections (valves, fuse plugs, 
etc.) for those openings. Threads are required on openings.
    (1) Threads must be clean cut, even, without checks, and to gauge.
    (2) Taper threads, when used, must be of length not less than as 
specified for American Standard taper pipe threads.
    (3) Straight threads having at least 6 engaged threads are 
authorized. Straight threads must have a tight fit and calculated shear 
strength of at least 10 times the test pressure of the cylinder. 
Gaskets, adequate to prevent leakage, are required.
    (i) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test, as follows:
    (1) The test must be by water-jacket, or other suitable methods, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy of either 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the test pressure. If, due to failure of the test 
apparatus the test pressure cannot be maintained the test may be 
repeated at a pressure increased by 10 percent or 100 pounds per square 
inch, whichever is the lower.
    (3) Permanent, volumetric expansion may not exceed 10 percent of 
the total volumetric expansion at test pressure.
    (4) Each cylinder must be tested to at least 5/3 times service 
pressure.
    (j) Flattening test. A flattening test must be performed on one 
cylinder taken at random out or each lot of 200 or less, by placing the 
cylinder between wedge shaped knife edges having a 60 deg. included 
angle, rounded to \1/2\-inch radius. The longitudinal axis of the 
cylinder must be at a 90-degree angle to 

[[Page 8332]]
knife edges during the test. For lots of 30 or less, flattening tests 
are authorized to be made on a ring at least 8 inches long cut from 
each cylinder and subjected to same heat treatment as the finished 
cylinder.
    (k) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material as follows:
    (1) The test is required on 2 specimens cut from 1 cylinder taken 
at random out of each lot of 200 or less. For lots of 30 or less, 
physical tests are authorized to be made on a ring at least 8 inches 
long cut from each cylinder and subjected to same heat treatment as the 
finished cylinder.
    (2) Specimens must conform to the following:
    (i) Gauge length of 8 inches with a width of not over 1\1/2\ 
inches, a gauge length of 2 inches with a width of not over 1\1/2\ 
inches, or a gauge length of at least 24 times thickness with width not 
over 6 times thickness is authorized when cylinder wall is not over \3/
16\ inch thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within 1 inch of each end of the reduced 
section.
    (iii) When size of cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold, by pressure only, not by blows. 
When specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2-percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch and the strain indicator reading must be set at the 
calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (l) Acceptable results for physical and flattening tests. Either of 
the following is an acceptable result:
    (1) An elongation at least 40 percent for a 2-inch gauge length or 
at least 20 percent in other cases and yield strength not over 73 
percent of tensile strength. In this instance, the flattening test is 
not required.
    (2) An elongation at least 20 percent for a 2-inch gauge length or 
10 percent in other cases and a yield strength not over 73 percent of 
tensile strength. In this instance, the flattening test is required, 
without cracking, to 6 times the wall thickness.
    (m) Leakage test. All spun cylinders and plugged cylinders must be 
tested for leakage by gas or air pressure after the bottom has been 
cleaned and is free from all moisture subject to the following 
conditions and limitations:
    (1) Pressure, approximately the same as but no less than service 
pressure, must be applied to one side of the finished bottom over an 
area of at least \1/16\ of the total area of the bottom but not less 
than \3/4\ inch in diameter, including the closure, for at least 1 
minute, during which time the other side of the bottom exposed to 
pressure must be covered with water and closely examined for 
indications of leakage. Except as provided in paragraph (n) of this 
section, a cylinder that is leaking must be rejected.
    (2) A spun cylinder is one in which an end closure in the finished 
cylinder has been welded by the spinning process.
    (3) A plugged cylinder is one in which a permanent closure in the 
bottom of a finished cylinder has been effected by a plug.
    (4) As a safety precaution, if the manufacturer elects to make this 
test before the hydrostatic test, the manufacturer should design the 
test apparatus so that the pressure is applied to the smallest area 
practicable, around the point of closure, and so as to use the smallest 
possible volume of air or gas.
    (n) Rejected cylinders. Reheat treatment is authorized for rejected 
cylinders. Subsequent thereto, cylinders must pass all prescribed tests 
to be acceptable. Repair by welding or spinning is not authorized. Spun 
cylinders rejected under the provisions of paragraph (m) of this 
section may be removed from the spun cylinder category by drilling to 
remove defective material, tapping and plugging.


Sec. 178.37  Specification 3AA and 3AAX seamless steel cylinders.

    (a) Type, size and service pressure. In addition to the 
requirements of Sec. 178.35, cylinders must conform to the following:
    (1) A DOT-3AA cylinder is a seamless steel cylinder with a water 
capacity (nominal) of not over 1,000 pounds and a service pressure of 
at least 150 pounds per square inch.
    (2) A DOT-3AAX cylinder is a seamless steel cylinder with a water 
capacity of not less than 1,000 pounds and a service pressure of at 
least 500 pounds per square inch, conforming to the following 
requirements:
    (i) Assuming the cylinder is to be supported horizontally at its 
two ends only and to be uniformly loaded over its entire length 
consisting of the weight per unit of length of the straight cylindrical 
portion filled with water and compressed to the specified test 
pressure; the sum of two times the maximum tensile stress in the bottom 
fibers due to bending, plus that in the same fibers (longitudinal 
stress), due to hydrostatic test pressure may not exceed 80 percent of 
the minimum yield strength of the steel at such maximum stress. Wall 
thickness must be increased when necessary to meet the requirement.
    (ii) To calculate the maximum tensile stress due to bending, the 
following formula must be used:

S=Mc/I

    (iii) To calculate the maximum longitudinal tensile stress due to 
hydrostatic test pressure, the following formula must be used:

S=A\1\P/A\2\

where:

S=tensile stress-p.s.i.;
M=bending moment-inch pounds (wl\2\)/8;
w=weight per inch of cylinder filled with water;
l=length of cylinder-inches;
c=radius (D)/(2) of cylinder-inches;
I=moment of inertia-0.04909 (D\4\-d\4\) inches fourth;
D=outside diameter-inches;
d=inside diameter-inches;
A\1\=internal area in cross section of cylinder-square inches;
A\2\=area of metal in cross section of cylinder-square inches;
P=hydrostatic test pressure-p.s.i.

    (b) Authorized steel. Open-hearth, basic oxygen, or electric steel 
of uniform 

[[Page 8333]]
quality must be used. A heat of steel made under the specifications in 
Table 1 of this paragraph (b), check chemical analysis of which is 
slightly out of the specified range, is acceptable, if satisfactory in 
all other respects, provided the tolerance shown in Table 2 of this 
paragraph (b) are not exceeded. When a carbon-boron steel is used, a 
hardenability test must be performed on the first and last ingot of 
each heat of steel. The results of this test must be recorded on the 
Record of Chemical Analysis of Material for Cylinders required by 
Sec. 178.35. This hardness test must be made \5/16\-inch from the 
quenched end of the Jominy quench bar and the hardness must be at least 
Rc 33 and no more than Rc 53. The following chemical analyses are 
authorized:

                                                             Table 1.--Authorized Materials                                                             
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                         Intermediate   
         Designation             4130X (percent)     NE-8630 (percent)   9115 (percent) (see    9125 (percent)       Carbon-boron          manganese    
                                   (see Note 1)         (see Note 1)           Note 1)           (see Note 1)          (percent)           (percent)    
--------------------------------------------------------------------------------------------------------------------------------------------------------
Carbon.......................  0.25/0.35..........  0.28/0.33..........  0.10/0.20..........  0.20/0.30.........  0.27-0.37.........  0.40 max.         
Manganese....................  0.40/0.90..........  0.70/0.90..........  0.50/0.75..........  0.50/0.75.........  0.80-1.40.........  1.35/1.65         
Phosphorus...................  0.04 max...........  0.04 max...........  0.04 max...........  0.04 max..........  0.035 max.........  0.04 max.         
Sulfur.......................  0.05 max...........  0.04 max...........  0.04 max...........  0.04 max..........  0.045 max.........  0.05 max.         
Silicon......................  0.15/0.35..........  0.20/0.35..........  0.60/0.90..........  0.60/0.90.........  0.3 max...........  0.10/0.30         
Chromium.....................  0.80/1.10..........  0.40/0.60..........  0.50/0.65..........  0.50/0.65.........  ..................  ..................
Molybdenum...................  0.15/0.25..........  0.15/0.25..........  ...................  ..................  ..................  ..................
Zirconium....................  ...................  ...................  0.05/0.15..........  0.05/0.15.........  ..................  ..................
Nickel.......................  ...................  0.40/0.70..........  ...................  ..................  ..................  ..................
Boron........................  ...................  ...................  ...................  ..................  0.0005/0.003        ..................
--------------------------------------------------------------------------------------------------------------------------------------------------------
Note 1: This designation may not be restrictive and the commercial steel is limited in analysis as shown in this Table 1.                               


                                       Table 2.--Check Analysis Tolerances                                      
----------------------------------------------------------------------------------------------------------------
                                                                                   Tolerance (percent) over the 
                                                                                    maximum limit or under the  
                                                   Limit or maximum specified              minimum limit        
                    Element                                 (percent)            -------------------------------
                                                                                   Under minimum   Over maximum 
                                                                                       limit           limit    
----------------------------------------------------------------------------------------------------------------
Carbon........................................  To 0.15 incl....................            0.02            0.03
                                                Over 0.15 to 0.40 incl..........             .03             .04
Manganese.....................................  To 0.60 incl....................             .03             .03
                                                Over 0.60 to 1.15 incl..........             .04             .04
                                                Over 1.15 to 2.50 incl..........             .05             .05
Phosphorus \1\................................  All ranges......................  ..............             .01
Sulphur.......................................  All ranges......................  ..............             .01
Silicon.......................................  To 0.30 incl....................             .02             .03
                                                Over 0.30 to 1.00 incl..........             .05             .05
Nickel........................................  To 1.00 incl....................             .03             .03
Chromium......................................  To 0.90 incl....................             .03             .03
                                                0.90 to 2.90 incl...............             .05             .05
Molybdenum....................................  To 0.20 incl....................             .01             .01
                                                Over 0.20 to 0.40...............             .02             .02
Zirconium.....................................  All ranges......................             .01             .05
----------------------------------------------------------------------------------------------------------------
\1\ Rephosphorized steels not subject to check analysis for phosphorus.                                         

    (c) Identification of material. Material must be identified by any 
suitable method except that plates and billets for hot-drawn cylinders 
must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No fissure or other defects is 
permitted that is likely to weaken the finished cylinder appreciably. A 
reasonably smooth and uniform surface finish is required. If not 
originally free from such defects, the surface may be machined or 
otherwise treated to eliminate these defects. The thickness of the 
bottoms of cylinders welded or formed by spinning is, under no 
condition, to be less than two times the minimum wall thickness of the 
cylindrical shell; such bottom thicknesses must be measured within an 
area bounded by a line representing the points of contact between the 
cylinder and floor when the cylinder is in a vertical position.
    (e) Welding or brazing. Welding or brazing for any purpose 
whatsoever is prohibited except as follows:
    (1) Welding or brazing is authorized for the attachment of 
neckrings and footrings which are non-pressure parts, and only to the 
tops and bottoms of cylinders having a service pressure of 500 pounds 
per square inch or less. Cylinders, neckrings, and footrings must be 
made of weldable steel, the carbon content of which may not exceed 0.25 
percent except in the case of 4130X steel which may be used with proper 
welding procedure.
    (2) As permitted in paragraph (d) of this section.
    (f) Wall thickness. The thickness of each cylinder must conform to 
the following:
    (1) For cylinders with a service pressure of less than 900 pounds, 
the wall stress may not exceed 24,000 pounds per square inch. A minimum 
wall thickness of 0.100 inch is required for any cylinder with an 
outside diameter of over 5 inches.
    (2) For cylinders with service pressure of 900 p.s.i. or more the 
minimum wall must be such that the wall stress at the 

[[Page 8334]]
minimum specified test pressure may not exceed 67 percent of the 
minimum tensile strength of the steel as determined from the physical 
tests required in paragraphs (k) and (l) of this section and must be 
not over 70,000 p.s.i.
    (3) Calculation must be made by the formula:

S=[P(1.3D \2\+0.4d \2\)]/(D \2\-d \2\)

where:

S=wall stress in pounds per square inch;
P=minimum test pressure prescribed for water jacket test or 450 pounds 
per square inch whichever is the greater;
D=outside diameter in inches;
d=inside diameter in inches.

    (g) Heat treatment. The completed cylinders must be uniformly and 
properly heat treated prior to tests. Heat treatment of cylinders of 
the authorized analyses must be as follows:
    (1) All cylinders must be quenched by oil, or other suitable medium 
except as provided in paragraph (g)(5) of this section.
    (2) The steel temperature on quenching must be that recommended for 
the steel analysis, but may not exceed 1750  deg.F.
    (3) All steels must be tempered at a temperature most suitable for 
that steel.
    (4) The minimum tempering temperature may not be less than 1000 
deg.F except as noted in paragraph (l)(vi) of this section.
    (5) Steel 4130X may be normalized at a temperature of 1650  deg.F 
instead of being quenched and cylinders so normalized need not be 
tempered.
    (6) Intermediate manganese steels may be tempered at temperatures 
not less than 1150  deg.F, and after heat treating each cylinder must 
be submitted to a magnetic test to detect the presence of quenching 
cracks. Cracked cylinders must be rejected and destroyed.
    (7) Except as otherwise provided in paragraph (g)(6) of this 
section, all cylinders, if water quenched or quenched with a liquid 
producing a cooling rate in excess of 80 percent of the cooling rate of 
water, must be inspected by the magnetic particle, dye penetrant or 
ultrasonic method to detect the presence of quenching cracks. Any 
cylinder designed to the requirements for specification 3AA and found 
to have a quenching crack must be rejected and may not be requalified. 
Cylinders designed to the requirements for specification 3AAX and found 
to have cracks must have cracks removed to sound metal by mechanical 
means. Such specification 3AAX cylinders will be acceptable if the 
repaired area is subsequently examined to assure no defect, and it is 
determined that design thickness requirements are met.
    (h) Openings in cylinders and connections (valves, fuse plugs, 
etc.) for those openings. Threads are required on openings.
    (1) Threads must be clean cut, even, without checks, and to gauge.
    (2) Taper threads, when used, must be of a length not less than as 
specified for American Standard taper pipe threads.
    (3) Straight threads having at least 6 engaged threads are 
authorized. Straight threads must have a tight fit and a calculated 
shear strength of at least 10 times the test pressure of the cylinder. 
Gaskets, adequate to prevent leakage, are required.
    (i) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy of either 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the test pressure. If, due to failure of the test 
apparatus, the test pressure cannot be maintained, the test may be 
repeated at a pressure increased by 10 percent or 100 pounds per square 
inch, whichever is the lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) Each cylinder must be tested to at least \5/3\ times the 
service pressure.
    (j) Flattening test. A flattening test must be performed on one 
cylinder taken at random out of each lot of 200 or less, by placing the 
cylinder between wedge shaped knife edges having a 60 deg. included 
angle, rounded to \1/2\-inch radius. The longitudinal axis of the 
cylinder must be at a 90-degree angle to knife edges during the test. 
For lots of 30 or less, flattening tests are authorized to be made on a 
ring at least 8 inches long cut from each cylinder and subjected to 
same heat treatment as the finished cylinder.
    (k) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material as follows:
    (1) The test is required on 2 specimens cut from 1 cylinder taken 
at random out of each lot of 200 or less. For lots of 30 or less, 
physical tests are authorized to be made on a ring at least 8 inches 
long cut from each cylinder and subjected to the same heat treatment as 
the finished cylinder.
    (2) Specimens must conform to the following:
    (i) Gauge length of 8 inches with a width of not over 1\1/2\ 
inches, a gauge length of 2 inches with a width of not over 1\1/2\ 
inches, or a gauge length of at least 24 times the thickness with width 
not over 6 times thickness when the thickness of the cylinder wall is 
not over \3/16\ inch.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within one inch of each end of the 
reduced section.
    (iii) When size of cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold, by pressure only, not by blows. 
When specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch, the strain indicator reading being set at the calculated 
corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (l) Acceptable results for physical and flattening tests. An 
acceptable result for physical and flattening tests is elongation at 
least 20 percent for 2 

[[Page 8335]]
inches of gauge length or at least 10 percent in other cases. 
Flattening is required without cracking to 6 times the wall thickness 
of the cylinder.
    (m) Leakage test. All spun cylinders and plugged cylinders must be 
tested for leakage by gas or air pressure after the bottom has been 
cleaned and is free from all moisture. Pressure, approximately the same 
as but no less than the service pressure, must be applied to one side 
of the finished bottom over an area of at least \1/16\ of the total 
area of the bottom but not less than \3/4\ inch in diameter, including 
the closure, for at least one minute, during which time the other side 
of the bottom exposed to pressure must be covered with water and 
closely examined for indications of leakage. Except as provided in 
paragraph (n) of this section, a cylinder must be rejected if there is 
any leaking.
    (1) A spun cylinder is one in which an end closure in the finished 
cylinder has been welded by the spinning process.
    (2) A plugged cylinder is one in which a permanent closure in the 
bottom of a finished cylinder has been effected by a plug.
    (3) As a safety precaution, if the manufacturer elects to make this 
test before the hydrostatic test, the manufacturer should design the 
test apparatus so that the pressure is applied to the smallest area 
practicable, around the point of closure, and so as to use the smallest 
possible volume of air or gas.
    (n) Rejected cylinders. Reheat treatment is authorized for rejected 
cylinders. Subsequent thereto, cylinders must pass all prescribed tests 
to be acceptable. Repair by welding or spinning is not authorized. Spun 
cylinders rejected under the provision of paragraph (m) of this section 
may be removed from the spun cylinder category by drilling to remove 
defective material, tapping and plugging.


Sec. 178.38  Specification 3B seamless steel cylinders.

    (a) Type, size, and service pressure. A DOT 3B cylinder is a 
seamless steel cylinder with a water capacity (nominal) of not over 
1,000 pounds and a service pressure of at least 150 to not over 500 
pounds per square inch.
    (b) Steel. Open-hearth or electric steel of uniform quality must be 
used. Content percent may not exceed the following: carbon, 0.55; 
phosphorus, 0.045; sulphur, 0.050.
    (c) Identification of material. Material must be identified by any 
suitable method except that plates and billets for hot-drawn cylinders 
must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No fissure or other defect is 
permitted that is likely to weaken the finished cylinder appreciably. A 
reasonably smooth and uniform surface finish is required. If not 
originally free from such defects, the surface may be machined or 
otherwise treated to eliminate these defects. The thickness of the 
bottoms of cylinders welded or formed by spinning is, under no 
condition, to be less than two times the minimum wall thickness of the 
cylindrical shell; such bottom thicknesses to be measured within an 
area bounded by a line representing the points of contact between the 
cylinder and floor when the cylinder is in a vertical position.
    (e) Welding or brazing. Welding or brazing for any purpose 
whatsoever is prohibited except as follows:
    (1) Welding or brazing is authorized for the attachment of 
neckrings and footrings which are non-pressure parts, and only to the 
tops and bottoms of cylinders having a service pressure of 500 pounds 
per square inch or less. Cylinders, neckrings, and footrings must be 
made of weldable steel, carbon content of which may not exceed 0.25 
percent except in the case of 4130X steel which may be used with proper 
welding procedure.
    (2) As permitted in paragraph (d) of this section.
    (f) Wall thickness. The wall stress may not exceed 24,000 pounds 
per square inch. The minimum wall thickness is 0.090 inch for any 
cylinder with an outside diameter of 6 inches. Calculation must be made 
by the following formula:

S=[P(1.3D \2\+0.4d \2\)]/(D \2\-d \2\)

where:
S=wall stress in pounds per square inch;
P=at least two times service pressure or 450 pounds per square inch, 
whichever is the greater;
D=outside diameter in inches;
d=inside diameter in inches.

    (g) Heat treatment. The completed cylinders must be uniformly and 
properly heat-treated prior to tests.
    (h) Openings in cylinders and connections (valves, fuse plugs, 
etc.) for those openings. Threads, conforming to the following, are 
required on all openings.
    (1) Threads must be clean cut, even, without checks, and to gauge.
    (2) Taper threads when used, must be of a length not less than as 
specified for American Standard taper pipe threads.
    (3) Straight threads having at least 4 engaged threads are 
authorized. Straight threads must have a tight fit, and calculated 
shear strength at least 10 times the test pressure of the cylinder. 
Gaskets, adequate to prevent leakage, are required.
    (i) Hydrostatic test. Cylinders must successfully withstand a 
hydrostatic test, as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy either of 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to insure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the test pressure. If, due to failure of the test 
apparatus, the test pressure cannot be maintained, the test may be 
repeated at a pressure increased by 10 percent or 100 pounds per square 
inch, whichever is the lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) Cylinders must be tested as follows:
    (i) Each cylinder; to at least 2 times service pressure; or
    (ii) 1 cylinder out of each lot of 200 or less; to at least 3 times 
service pressure. Others must be examined under pressure of 2 times 
service pressure and show no defect.
    (j) Flattening test. A flattening test must be performed on one 
cylinder taken at random out or each lot of 200 or less, by placing the 
cylinder between wedge shaped knife edges having a 60 deg. included 
angle, rounded to \1/2\-inch radius. The longitudinal axis of the 
cylinder must be at a 90-degree angle to knife edges during the test. 
For lots of 30 or less, flattening tests are authorized to be made on a 
ring at least 8 inches long cut from each cylinder and subjected to 
same heat treatment as the finished cylinder.
    (k) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material, as follows:
    (1) The test is required on 2 specimens cut from 1 cylinder taken 
at random out of each lot of 200 or less. For lots of 30 or less, 
physical tests are authorized to be made on a ring at least 8 inches 
long cut from each cylinder and subjected to same heat treatment as the 
finished cylinder.
    (2) Specimens must conform to the following: 
    
[[Page 8336]]

    (i) Gauge length of 8 inches with a width of not over 1\1/2\ 
inches; or a gauge length of 2 inches with a width of not over 1\1/2\ 
inches; or a gauge length at least 24 times the thickness with a width 
not over 6 times thickness is authorized when a cylinder wall is not 
over \3/16\ inch thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within one inch of each end of the 
reduced section.
    (iii) When size of cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold, by pressure only, not by blows. 
When specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch, and the strain indicator reading being set at the 
calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (l) Acceptable results for physical and flattening tests. Either of 
the following is an acceptable result:
    (1) An elongation of at least 40 percent for a 2-inch gauge length 
or at least 20 percent in other cases and yield strength not over 73 
percent of tensile strength. In this instance, the flattening test is 
not required.
    (2) An elongation of at least 20 percent for a 2-inch gauge length 
or 10 percent in other cases and yield strength not over 73 percent of 
tensile strength. Flattening is required, without cracking, to 6 times 
the wall thickness.
    (m) Leakage test. All spun cylinders and plugged cylinders must be 
tested for leakage by gas or air pressure after the bottom has been 
cleaned and is free from all moisture, subject to the following 
conditions and limitations:
    (1) Pressure, approximately the same as but no less than service 
pressure, must be applied to one side of the finished bottom over an 
area of at least \1/16\ of the total area of the bottom but not less 
than \3/4\ inch in diameter, including the closure, for at least one 
minute, during which time the other side of the bottom exposed to 
pressure must be covered with water and closely examined for 
indications of leakage. Except as provided in paragraph (n) of this 
section, a cylinder must be rejected if there is any leaking.
    (2) A spun cylinder is one in which an end closure in the finished 
cylinder has been welded by the spinning process.
    (3) A plugged cylinder is one in which a permanent closure in the 
bottom of a finished cylinder has been effected by a plug.
    (4) As a safety precaution, if the manufacturer elects to make this 
test before the hydrostatic test, he should design his apparatus so 
that the pressure is applied to the smallest area practicable, around 
the point of closure, and so as to use the smallest possible volume of 
air or gas.
    (n) Rejected cylinders. Reheat treatment of rejected cylinders is 
authorized. Subsequent thereto, cylinders must pass all prescribed 
tests to be acceptable. Repair by welding or spinning is not 
authorized. Spun cylinders rejected under the provisions of paragraph 
(m) of this section may be removed from the spun cylinder category by 
drilling to remove defective material, tapping and plugging.
    (o) Marking. Markings may be stamped into the sidewalls of 
cylinders having a service pressure of 150 psi if all of the following 
conditions are met:
    (1) Wall stress at test pressure may not exceed 24,000 psi.
    (2) Minimum wall thickness must be not less than 0.090 inch.
    (3) Depth of stamping must be no greater than 15 percent of the 
minimum wall thickness, but may not exceed 0.015 inch.
    (4) Maximum outside diameter of cylinder may not exceed 5 inches.
    (5) Carbon content of cylinder may not exceed 0.25 percent. If the 
carbon content exceeds 0.25 percent, the complete cylinder must be 
normalized after stamping.
    (6) Stamping must be adjacent to the top head.


Sec. 178.39  Specification 3BN seamless nickel cylinders.

    (a) Type, size and service pressure. A DOT 3BN cylinder is a 
seamless nickel cylinder with a water capacity (nominal) not over 125 
pounds water capacity (nominal) and a service pressure at least 150 to 
not over 500 pounds per square inch.
    (b) Nickel. The percentage of nickel plus cobalt must be at least 
99.0 percent.
    (c) Identification of material. The material must be identified by 
any suitable method except that plates and billets for hot-drawn 
cylinders must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is permitted that is likely 
to weaken the finished cylinder appreciably. A reasonably smooth and 
uniform surface finish is required. Cylinders closed in by spinning 
process are not authorized.
    (e) Welding or brazing. Welding or brazing for any purpose 
whatsoever is prohibited except that welding is authorized for the 
attachment of neckrings and footrings which are nonpressure parts, and 
only to the tops and bottoms of cylinders. Neckrings and footrings must 
be of weldable material, the carbon content of which may not exceed 
0.25 percent. Nickel welding rod must be used.
    (f) Wall thickness. The wall stress may not exceed 15,000 pounds 
per square inch. A minimum wall thickness of 0.100 inch is required for 
any cylinder over 5 inches in outside diameter. Wall stress calculation 
must be made by using the following formula:

S=[P(1.3D2+0.4d2)]/(D2-d2)

where:

S=Wall stress in pounds per square inch;
P=Minimum test pressure prescribed for water jacket test or 450 pounds 
per square inch whichever is the greater;
D=Outside diameter in inches;
d=Inside diameter in inches.

    (g) Heat treatment. The completed cylinders must be uniformly and 
properly heat-treated prior to tests.
    (h) Openings in cylinders and connections (valves, fuse plugs, 
etc.) for those openings. Threads conforming to the following are 
required on openings.
    (1) Threads must be clean cut, even, without checks, and to gauge. 
    
[[Page 8337]]

    (2) Taper threads, when used, to be of length not less than as 
specified for American Standard taper pipe threads.
    (3) Straight threads having at least 6 engaged threads are 
authorized. Straight threads must have a tight fit and a calculated 
shear strength of at least 10 times the test pressure of the cylinder. 
Gaskets, adequate to prevent leakage, are required.
    (i) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test, as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy either of 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the test pressure. If, due to failure of the test 
apparatus, the test pressure cannot be maintained, the test may be 
repeated at a pressure increased by 10 percent or 100 pounds per square 
inch, whichever is the lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) Each cylinder must be tested to at least 2 times service 
pressure.
    (j) Flattening test. A flattening test must be performed on one 
cylinder taken at random out or each lot of 200 or less, by placing the 
cylinder between wedge shaped knife edges having a 60 deg. included 
angle, rounded to \1/2\ inch radius. The longitudinal axis of the 
cylinder must be at a 90-degree angle to knife edges during the test. 
For lots of 30 or less, flattening tests are authorized to be made on a 
ring at least 8 inches long cut from each cylinder and subjected to 
same heat treatment as the finished cylinder.
    (k) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material, as follows:
    (1) The test is required on 2 specimens cut from 1 cylinder taken 
at random out of each lot of 200 or less. For lots of 30 or less, 
physical tests are authorized to be made on a ring at least 8 inches 
long cut from each cylinder and subjected to same heat treatment as the 
finished cylinder.
    (2) Specimens must conform to the following:
    (i) A gauge length of 8 inches with a width of not over 1\1/2\ 
inches, a gauge length of 2 inches with a width of not over 1\1/2\ 
inches, or a gauge length of at least 24 times the thickness with a 
width not over 6 times thickness is authorized when a cylinder wall is 
not over \3/16\ inch thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within one inch of each end of the 
reduced section.
    (iii) When size of cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold, by pressure only, not by blows. 
When specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch, and the strain indicator reading must be set at the 
calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (l) Acceptable results for physical and flattening tests. Either of 
the following is an acceptable result:
    (1) An elongation of at least 40 percent for a 2 inch gauge length 
or at least 20 percent in other cases and yield point not over 50 
percent of tensile strength. In this instance, the flattening test is 
not required.
    (2) An elongation of at least 20 percent for a 2 inch gauge length 
or 10 percent in other cases and a yield point not over 50 percent of 
tensile strength. Flattening is required, without cracking, to 6 times 
the wall thickness.
    (m) Rejected cylinders. Reheat treatment is authorized for rejected 
cylinders. Subsequent thereto, cylinders must pass all prescribed tests 
to be acceptable. Repair by welding is not authorized.


Sec. 178.42  Specification 3E seamless steel cylinders.

    (a) Type, size, and service pressure. A DOT 3E cylinder is a 
seamless steel cylinder with an outside diameter not greater than 2 
inches nominal, a length less than 2 feet and a service pressure of 
1,800 pounds per square inch.
    (b) Steel. Open-hearth or electric steel of uniform quality must be 
used. Content percent may not exceed the following: Carbon, 0.55; 
phosphorus, 0.045; sulphur, 0.050.
    (c) Identification of steel. Materials must be identified by any 
suitable method.
    (d) Manufacture. Cylinders must be manufactured by best appliances 
and methods. No defect is permitted that is likely to weaken the 
finished cylinder appreciably. A reasonably smooth and uniform surface 
finish is required. The thickness of the spun bottom is, under no 
condition, to be less than two times the minimum wall thickness of the 
cylindrical shell; such bottom thickness must be measured within an 
area bounded by a line representing the points of contact between the 
cylinder and floor when the cylinder is in a vertical position.
    (e) Openings in cylinders and connections (valves, fuse plugs, 
etc.) for those openings. Threads conforming to the following are 
required on openings.
    (1) Threads must be clean cut, even, without checks, and to gauge.
    (2) Taper threads, when used, must be of length not less than as 
specified for American Standard taper pipe threads.
    (3) Straight threads having at least 4 engaged threads are 
authorized. Straight threads must have a tight fit and a calculated 
shear strength of at least 10 times the test pressure of the cylinder. 
Gaskets, adequate to prevent leakage, are required.
    (f) Hydrostatic test. Cylinders must be tested as follows:
    (1) One cylinder out of each lot of 500 or less must be subjected 
to a hydrostatic pressure of 6,000 pounds per square inch or higher.
    (2) The cylinder referred to in paragraph (f)(1) of this section 
must burst at a pressure higher than 6,000 pounds per square inch 
without fragmenting or otherwise showing lack of ductility, or must 
hold a pressure of 

[[Page 8338]]
12,000 pounds per square inch for 30 seconds without bursting. In which 
case, it must be subjected to a flattening test without cracking to six 
times wall thickness between knife edges, wedge shaped 60 degree angle, 
rounded out to a \1/2\ inch radius. The inspector's report must be 
suitably changed to show results of latter alternate and flattening 
test.
    (3) Other cylinders must be examined under pressure of at least 
3,000 pounds per square inch and not to exceed 4,500 pounds per square 
inch and show no defect. Cylinders tested at a pressure in excess of 
3,600 pounds per square inch must burst at a pressure higher than 7,500 
pounds per square inch when tested as specified in paragraph (f)(2) of 
this section. The pressure must be maintained for at least 30 seconds 
and sufficiently longer to ensure complete examination.
    (g) Leakage test. All spun cylinders and plugged cylinders must be 
tested for leakage by gas or air pressure after the bottom has been 
cleaned and is free from all moisture subject to the following 
conditions and limitations:
    (1) A pressure, approximately the same as but not less than the 
service pressure, must be applied to one side of the finished bottom 
over an area of at least \1/16\ of the total area of the bottom but not 
less than \3/4\ inch in diameter, including the closure, for at least 
one minute, during which time the other side of the bottom exposed to 
pressure must be covered with water and closely examined for 
indications of leakage. Accept as provided in paragraph (h) of this 
section, a cylinder must be rejected if there is any leakage.
    (2) A spun cylinder is one in which an end closure in the finished 
cylinder has been welded by the spinning process.
    (3) A plugged cylinder is one in which a permanent closure in the 
bottom of a finished cylinder has been effected by a plug.
    (4) As a safety precaution, if the manufacturer elects to make this 
test before the hydrostatic test, the manufacturer shall design the 
test apparatus so that the pressure is applied to the smallest area 
practicable, around the point of closure, and so as to use the smallest 
possible volume of air or gas.
    (h) Rejected cylinders. Reheat treatment is authorized for rejected 
cylinders. Subsequent thereto, cylinders must pass all prescribed tests 
to be acceptable. Repair by welding or spinning is not authorized. Spun 
cylinders rejected under the provisions of paragraph (g) of this 
section may be removed from the spun cylinder category by drilling to 
remove defective material, tapping and plugging.
    (i) Marking. Markings required by Sec. 178.35 must be stamped 
plainly and permanently on the shoulder, top head, neck or sidewall of 
each cylinder.


Sec. 178.44  Specification 3HT seamless steel cylinders for aircraft 
use.

    (a) Type, size and service pressure. A DOT 3HT cylinder is a 
seamless steel cylinder with a water capacity (nominal) of not over 150 
pounds and a service pressure of at least 900 pounds per square inch.
    (b) Authorized steel. Open hearth or electric furnace steel of 
uniform quality must be used. A heat of steel made under the 
specifications listed in Table 1 of this paragraph (b), check chemical 
analysis of which is slightly out of the specified range, is 
acceptable, if satisfactory in all other respects, provided the 
tolerances shown in Table 2 of this paragraph (b) are not exceeded. 
Grain size 6 or finer according to ASTM Spec. E19-46. Steel of the 
following chemical analysis is authorized:

                                         Table 1.--Authorized Materials                                         
                                                                                                                
                                                                                                                
Designation................................................  AISI 4130 (percent)                                
Carbon.....................................................  0.28/0.33                                          
Manganese..................................................  0.40/0.60                                          
Phosphorus.................................................  0.040 maximum                                      
Sulfur.....................................................  0.040 maximum                                      
Silicon....................................................  0.15/0.35                                          
Chromium...................................................  0.80/1.10                                          
Molybdenum.................................................  0.18/0.25.                                         


                                       Table 2--Check Analysis Tolerances                                       
----------------------------------------------------------------------------------------------------------------
                                                                                   Tolerance (percent) over the 
                                                                                    maximum limit or under the  
                                                  Limit or maximum specified               minimum limit        
                  Element                                 (percent)              -------------------------------
                                                                                   Under minimum   Over maximum 
                                                                                       limit           limit    
----------------------------------------------------------------------------------------------------------------
Carbon.....................................  Over 0.15 to 0.40 incl.............             .03             .04
Manganese..................................  To 0.60 incl.......................             .03             .03
Phosphorus \1\.............................  All ranges.........................  ..............             .01
Sulphur....................................  All ranges.........................  ..............             .01
Silicon....................................  To 0.30 incl.......................             .02             .03
                                             Over 0.30 to 1.00 incl.............             .05             .05
Chromium...................................  To 0.90 incl.......................             .03             .03
                                             Over 0.90 to 2.10 incl.............             .05             .05
Molybdenum.................................  To 0.20 incl.......................             .01             .01
                                             Over 0.20 to 0.40 incl.............             .02             .02
----------------------------------------------------------------------------------------------------------------
\1\ Rephosphorized steels not subject to check analysis for phosphorus.                                         

    (c) Identification of material. Material must be identified by any 
suitable method. Steel stamping of heat identifications may not be made 
in any area which will eventually become the side wall of the cylinder. 
Depth of stamping may not encroach upon the minimum prescribed wall 
thickness of the cylinder. 

[[Page 8339]]

    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No fissure or other defect is 
permitted that is likely to weaken the finished container appreciably. 
The general surface finish may not exceed a roughness of 250 RMS. 
Individual irregularities such as draw marks, scratches, pits, etc., 
should be held to a minimum consistent with good high stress pressure 
vessel manufacturing practices. If the cylinder is not originally free 
of such defects or does not meet the finish requirements, the surface 
may be machined or otherwise treated to eliminate these defects. The 
point of closure of cylinders closed by spinning may not be less than 
two times the prescribed wall thickness of the cylindrical shell. The 
cylinder end contour must be hemispherical or ellipsoidal with a ratio 
of major-to-minor axis not exceeding two to one and with the concave 
side to pressure.
    (e) Welding or brazing. Welding or brazing for any purpose 
whatsoever is prohibited, except that welding by spinning is permitted 
to close the bottom of spun cylinders. Machining or grinding to produce 
proper surface finish at point of closure is required.
    (f) Wall thickness. (1) Minimum wall thickness for any cylinder 
must be 0.050 inch. The minimum wall thickness must be such that the 
wall stress at the minimum specified test pressure may not exceed 75 
percent of the minimum tensile strength of the steel as determined from 
the physical tests required in paragraph (m) of this section and may 
not be over 105,000 psi.
    (2) Calculations must be made by the formula:

S=[P(1.3D2+0.4d 2)]/(D 2-d 2)

where:
S=Wall stress in pounds per square inch;
P=Minimum test pressure prescribed for water jacket test;
D=Outside diameter in inches;
d=Inside diameter in inches.

    (3) Wall thickness of hemispherical bottoms only permitted to 90 
percent of minimum wall thickness of cylinder sidewall but may not be 
less than 0.050 inch. In all other cases, thickness to be no less than 
prescribed minimum wall.
    (g) Heat treatment. The completed cylinders must be uniformly and 
properly heated prior to tests. Heat treatment of the cylinders of the 
authorized analysis must be as follows:
    (1) All cylinders must be quenched by oil, or other suitable 
medium.
    (2) The steel temperature on quenching must be that recommended for 
the steel analysis, but may not exceed 1750 deg. F.
    (3) The steel must be tempered at a temperature most suitable for 
the particular steel analysis but not less than 850 deg. F.
    (4) All cylinders must be inspected by the magnetic particle or dye 
penetrant method to detect the presence of quenching cracks. Any 
cylinder found to have a quenching crack must be rejected and may not 
be requalified.
    (h) Openings in cylinders and connections (valves, fuse plugs, 
etc.) for those openings. Threads conforming to the following are 
required on openings:
    (1) Threads must be clean cut, even, without cracks, and to gauge.
    (2) Taper threads, when used, must be of length not less than as 
specified for National Gas Tapered Thread (NGT) as required by American 
Standard Compressed Gas Cylinder Valve Outlet and Inlet Connections.
    (3) Straight threads having at least 6 engaged threads are 
authorized. Straight threads must have a tight fit and a calculated 
shear stress of at least 10 times the test pressure of the cylinder.
    Gaskets, adequate to prevent leakage, are required.
    (i) Hydrostatic test. Each cylinder must withstand a hydrostatic 
test, as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. Pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy either of 1 percent of 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat treatment and previous to the official test may not 
exceed 90 percent of the test pressure. If, due to failure of the test 
apparatus, the test pressure cannot be maintained, the test may be 
repeated at a pressure increased by 10 percent or 100 pounds per square 
inch, which ever is the lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) Each cylinder must be tested to at least 5/3 times service 
pressure.
    (j) Cycling tests. Prior to the initial shipment of any specific 
cylinder design, cyclic pressurization tests must have been performed 
on at least three representative samples without failure as follows:
    (1) Pressurization must be performed hydrostatically between 
approximately zero psig and the service pressure at a rate not in 
excess of 10 cycles per minute. Adequate recording instrumentation must 
be provided if equipment is to be left unattended for periods of time.
    (2) Tests prescribed in paragraph (j)(1) of this section must be 
repeated on one random sample out of each lot of cylinders. The 
cylinder may then be subjected to a burst test.
    (3) A lot is defined as a group of cylinders fabricated from the 
same heat of steel, manufactured by the same process and heat treated 
in the same equipment under the same conditions of time, temperature, 
and atmosphere, and may not exceed a quantity of 200 cylinders.
    (4) All cylinders used in cycling tests must be destroyed.
    (k) Burst test. One cylinder taken at random out of each lot of 
cylinders must be hydrostatically tested to destruction.
    (l) Flattening test. A flattening test must be performed on one 
cylinder taken at random out or each lot of 200 or less, by placing the 
cylinder between wedge shaped knife edges having a 60 deg. included 
angle, rounded to \1/2\-inch radius. The longitudinal axis of the 
cylinder must be at a 90-degree angle to knife edges during the test. 
For lots of 30 or less, flattening tests are authorized to be made on a 
ring at least 8 inches long cut from each cylinder and subjected to 
same heat treatment as the finished cylinder.
    (m) Physical tests. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material , as follows:
    (1) Test is required on 2 specimens cut from 1 cylinder taken at 
random out of each lot of cylinders.
    (2) Specimens must conform to the following:
    (i) A gauge length of at least 24 times the thickness with a width 
not over six times the thickness. The specimen, exclusive of grip ends, 
may not be flattened. Grip ends may be flattened to within one inch of 
each end of the reduced section. When size of cylinder does not permit 
securing straight specimens, the specimens may be taken in any location 
or direction and may be straightened or flattened cold by pressure 
only, not by blows. When specimens are so taken and prepared, the 
inspector's report must show in connection with the record of physical 
tests detailed information in regard to such specimens.
    (ii) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. 

[[Page 8340]]

    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch, the strain indicator reading being set at the calculated 
corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (n) Magnetic particle inspection. Inspection must be performed on 
the inside of each container before closing and externally on each 
finished container after heat treatment. Evidence of discontinuities, 
which in the opinion of a qualified inspector may appreciably weaken or 
decrease the durability of the cylinder, must be cause for rejection.
    (o) Leakage test. All spun cylinders and plugged cylinders must be 
tested for leakage by dry gas or dry air pressure after the bottom has 
been cleaned and is free from all moisture, subject to the following 
conditions and limitations:
    (1) Pressure, approximately the same as but not less than service 
pressure, must be applied to one side of the finished bottom over an 
area of at least \1/16\ of the total area of the bottom but not less 
than \3/4\ inch in diameter, including the closure, for at least one 
minute, during which time the other side of the bottom exposed to 
pressure must be covered with water and closely examined for 
indications of leakage. Except as provided in paragraph (q) of this 
section, a cylinder must be rejected if there is leakage.
    (2) A spun cylinder is one in which an end closure in the finished 
cylinder has been welded by the spinning process.
    (3) A plugged cylinder is one in which a permanent closure in the 
bottom of a finished cylinder has been effected by a plug.
    (4) As a safety precaution, if the manufacturer elects to make this 
test before the hydrostatic test, the manufacturer should design the 
test apparatus so that the pressure is applied to the smallest area 
practicable, around the point of closure, and so as to use the smallest 
possible volume of air or gas.
    (p) Acceptable results of tests. Results of the flattening test, 
physical tests, burst test, and cycling test must conform to the 
following:
    (1) Flattening required without cracking to ten times the wall 
thickness of the cylinder.
    (2) Physical tests:
    (i) An elongation of at least 6 percent for a gauge length of 24 
times the wall thickness.
    (ii) The tensile strength may not exceed 165,000 p.s.i.
    (3) The burst pressure must be at least \3/4\ times the test 
pressure.
    (4) Cycling-at least 10,000 pressurizations.
    (q) Rejected cylinders. Reheat treatment is authorized for rejected 
cylinders. Subsequent thereto, cylinders must pass all prescribed tests 
to be acceptable. Repair by welding or spinning is not authorized. For 
each cylinder subjected to reheat treatment during original 
manufacture, sidewall measurements must be made to verify that the 
minimum sidewall thickness meets specification requirements after the 
final heat treatment.
    (r) Marking. (1) Cylinders must be marked by low stress type steel 
stamping in an area and to a depth which will insure that the wall 
thickness measured from the root of the stamping to the interior 
surface is equal to or greater than the minimum prescribed wall 
thickness. Stamping must be permanent and legible. Stamping on side 
wall not authorized.
    (2) The rejection elastic expansion (REE), in cubic centimeters 
(cc), must be marked on the cylinder near the date of test. The REE for 
a cylinder is 1.05 times its original elastic expansion.
    (3) Name plates are authorized, provided that they can be 
permanently and securely attached to the cylinder. Attachment by either 
brazing or welding is not permitted. Attachment by soldering is 
permitted provided steel temperature does not exceed 500  deg.F.
    (s) Inspector's report. In addition to the requirements of 
Sec. 178.35, the inspector's report must indicate the rejection elastic 
expansion (REE), in cubic centimeters (cc).


Sec. 178.45  Specification 3T seamless steel cylinder.

    (a) Type, size, and service pressure. A DOT 3T cylinder is a 
seamless steel cylinder with a minimum water capacity of 1,000 pounds 
and a minimum service pressure of 1,800 p.s.i. Each cylinder must have 
integrally formed heads concave to pressure at both ends. The inside 
head shape must be hemispherical, ellipsoidal in which the major axis 
is two times the minor axis, or a dished shape falling within these two 
limits. Permanent closures formed by spinning are prohibited.
    (b) Material, steel. Only open hearth, basic oxygen, or electric 
furnace process steel of uniform quality is authorized. The steel 
analysis must conform to the following:

                                               Analysis Tolerances                                              
----------------------------------------------------------------------------------------------------------------
                                                                                          Check analysis        
                  Element                               Ladle analysis           -------------------------------
                                                                                       Under           Over     
----------------------------------------------------------------------------------------------------------------
Carbon.....................................  0.35 to 0.50.......................            0.03            0.04
Manganese..................................  0.75 to 1.05.......................             .04             .04
Phosphorus (max)...........................  0.035..............................  ..............             .01
Sulphur (max)..............................  .04................................  ..............             .01
Silicon....................................  0.15 to 0.35.......................             .02             .03
Chromium...................................  0.80 to 1.15.......................             .05             .05
Molybdenum.................................  0.15 to 0.25.......................             .02             .02
----------------------------------------------------------------------------------------------------------------

    (1) A heat of steel made under the specifications in the table in 
this paragraph (b), the ladle analysis of which is slightly out of the 
specified range, is acceptable if satisfactory in all other aspects. 
However, the check 

[[Page 8341]]
analysis tolerances shown in the table in this paragraph (b) may not be 
exceeded except as approved by the Department.
    (2) Material with seams, cracks, laminations, or other injurious 
defects is not permitted.
    (3) Material used must be identified by any suitable method.
    (c) Manufacture. General manufacturing requirements are as follows:
    (1) Surface finish must be uniform and reasonably smooth.
    (2) Inside surfaces must be clean, dry, and free of loose 
particles.
    (3) No defect of any kind is permitted if it is likely to weaken a 
finished cylinder.
    (4) If the cylinder surface is not originally free from the 
defects, the surface may be machined or otherwise treated to eliminate 
these defects provided the minimum wall thickness is maintained.
    (5) Welding or brazing on a cylinder is not permitted.
    (d) Wall thickness. The minimum wall thickness must be such that 
the wall stress at the minimum specified test pressure does not exceed 
67 percent of the minimum tensile strength of the steel as determined 
by the physical tests required in paragraphs (j) and (k) of this 
section. A wall stress of more than 90,500 p.s.i. is not permitted. The 
minimum wall thickness for any cylinder may not be less than 0.225 
inch.
    (1) Calculation of the stress for cylinders must be made by the 
following formula:

S=[P(1.3D2+0.4d2)]/(D2-d2)

where:

S=Wall stress in pounds per square inch;
P=Minimum test pressure, at least 5/3 service pressure;
D=Outside diameter in inches;
d=Inside diameter in inches.

    (2) Each cylinder must meet the following additional requirement 
which assumes a cylinder horizontally supported at its two ends and 
uniformly loaded over its entire length. This load consists of the 
weight per inch of length of the straight cylindrical portion filled 
with water compressed to the specified test pressure. The wall 
thickness must be increased when necessary to meet this additional 
requirement:
    (i) The sum of two times the maximum tensile stress in the bottom 
fibers due to bending (see paragraph (d)(2)(ii) of this section), plus 
the maximum tensile stress in the same fibers due to hydrostatic 
testing (see paragraph (d)(2)(iii) of this section) may not exceed 80 
percent of the minimum yield strength of the steel at this maximum 
stress.
    (ii) The following formula must be used to calculate the maximum 
tensile stress due to bending:

S=Mc/I

where:

S=Tensile stress in pounds per square inch;
M=Bending moment in inch-pounds (wl2/8);
I=Moment of inertia-0.04909 (D4-d4) in inches fourth;
c=Radius (D/2) of cylinder in inches;
w=Weight per inch of cylinder filled with water;
l=Length of cylinder in inches;
D=Outside diameter in inches;
d=Inside diameter in inches.

    (iii) The following formula must be used to calculate the maximum 
longitudinal tensile stress due to hydrostatic test pressure:

S=A1P/A2

where:

S=Tensile stress in pounds per square inch;
A1=Internal area in cross section of cylinder in square inches;
P=Hydrostatic test pressure in pounds per square, inch;
A2=Area of metal in cross section of cylinder in square inches.

    (e) Heat treatment. Each completed cylinder must be uniformly and 
properly heat treated prior to testing, as follows:
    (1) Each cylinder must be heated and held at the proper temperature 
for at least one hour per inch of thickness based on the maximum 
thickness of the cylinder and then quenched in a suitable liquid medium 
having a cooling rate not in excess of 80 percent of water. The steel 
temperature on quenching must be that recommended for the steel 
analysis, but it must never exceed 1750  deg.F. (2) After quenching, 
each cylinder must be reheated to a temperature below the 
transformation range but not less than 1050  deg.F., and must be held 
at this temperature for at least one hour per inch of thickness based 
on the maximum thickness of the cylinder. Each cylinder must then be 
cooled under conditions recommended for the steel.
    (f) Openings. Openings in cylinders must comply with the following:
    (1) Openings are permitted on heads only.
    (2) The size of any centered opening in a head may not exceed one 
half the outside diameter of the cylinder.
    (3) Openings in a head must have ligaments between openings of at 
least three times the average of their hole diameter. No off-center 
opening may exceed 2.625 inches in diameter.
    (4) All openings must be circular.
    (5) All openings must be threaded. Threads must be in compliance 
with the following:
    (i) Each thread must be clean cut, even, without any checks, and to 
gauge.
    (ii) Taper threads, when used, must be the American Standard Pipe 
thread (NPT) type and must be in compliance with the requirements of 
NBS Handbook H-28, Part II, Section VII.
    (iii) Taper threads conforming to National Gas Taper thread (NGT) 
standards must be in compliance with the requirements of NBS Handbook 
H-28, Part II, Sections VII and IX.
    (iv) Straight threads conforming with National Gas Straight thread 
(NGS) standards are authorized. These threads must be in compliance 
with the requirements of NBS Handbook H-28, Part II, Sections VII and 
IX.
    (g) Hydrostatic test. Each cylinder must be tested at an internal 
pressure by the water jacket method or other suitable method, 
conforming to the following requirements:
    (1) The testing apparatus must be operated in a manner that will 
obtain accurate data. Any pressure gauge used must permit reading to an 
accuracy of one percent. Any expansion gauge used must permit reading 
of the total expansion to an accuracy of one percent.
    (2) Any internal pressure applied to the cylinder after heat 
treatment and before the official test may not exceed 90 percent of the 
test pressure.
    (3) The pressure must be maintained sufficiently long to assure 
complete expansion of the cylinder. In no case may the pressure be held 
less than 30 seconds.
    (4) If, due to failure of the test apparatus, the required test 
pressure cannot be maintained, the test must be repeated at a pressure 
increased by 10 percent or 100 p.s.i., whichever is lower or, the 
cylinder must be reheat treated.
    (5) Permanent volumetric expansion of the cylinder may not exceed 
10 percent of its total volumetric expansion at the required test 
pressure.
    (6) Each cylinder must be tested to at least 5/3 times its service 
pressure.
    (h) Ultrasonic examination. After the hydrostatic test, the 
cylindrical section of each vessel must be examined in accordance with 
ASTM Standard A-388-67 using the angle beam technique. The equipment 
used must be calibrated to detect a notch equal to five percent of the 
design minimum wall thickness. Any discontinuity indication greater 
than that produced by the five percent notch must be cause for 
rejection of the 

[[Page 8342]]
cylinder unless the discontinuity is repaired within the requirements 
of this specification.
    (i) Basic requirements for tension and Charpy impact tests. 
Cylinders must be subjected to a tension and Charpy impact as follows:
    (1) When the cylinders are heat treated in a batch furnace, two 
tension specimens and three Charpy impact specimens must be tested from 
one of the cylinders or a test ring from each batch. The lot size 
represented by these tests may not exceed 200 cylinders.
    (2) When the cylinders are heat treated in a continuous furnace, 
two tension specimens and three Charpy impact specimens must be tested 
from one of the cylinders or a test ring from each four hours or less 
of production. However, in no case may a test lot based on this 
production period exceed 200 cylinders.
    (3) Each specimen for the tension and Charpy impact tests must be 
taken from the side wall of a cylinder or from a ring which has been 
heat treated with the finished cylinders of which the specimens must be 
representative. The axis of the specimens must be parallel to the axis 
of the cylinder. Each cylinder or ring specimen for test must be of the 
same diameter, thickness, and metal as the finished cylinders they 
represent. A test ring must be at least 24 inches long with ends 
covered during the heat treatment process so as to simulate the heat 
treatment process of the finished cylinders it represents.
    (4) A test cylinder or test ring need represent only one of the 
heats in a furnace batch provided the other heats in the batch have 
previously been tested and have passed the tests and that such tests do 
not represent more than 200 cylinders from any one heat.
    (5) The test results must conform to the requirements specified in 
paragraphs (j) and (k) of this section.
    (6) When the test results do not conform to the requirements 
specified, the cylinders represented by the tests may be reheat treated 
and the tests repeated. Paragraph (i)(5) of this section applies to any 
retesting.
    (j) Basic conditions for acceptable physical testing. The following 
criteria must be followed to obtain acceptable physical test results:
    (1) Each tension specimen must have a gauge length of two inches 
with a width not exceeding one and one-half inches. Except for the grip 
ends, the specimen may not be flattened. The grip ends may be flattened 
to within one inch of each end of the reduced section.
    (2) A specimen may not be heated after heat treatment specified in 
paragraph (d) of this section.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gage length.
    (i) This yield strength must be determined by the ``offset'' method 
or the ``extension under load'' method described in ASTM Standard E8-
69.
    (ii) For the ``extension under load'' method, the total strain (or 
extension under load) corresponding to the stress at which the 0.2 
percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gage length under 
appropriate load and adding thereto 0.2 percent of the gage length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. However, when the degree of accuracy of this method is 
questionable the entire stress-strain diagram must be plotted and the 
yield strength determined from the 0.2 percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set with the specimen under a stress of 12,000 p.s.i. and the 
strain indicator reading set at the calculated corresponding strain.
    (iv) The cross-head speed of the testing machine may not exceed \1/
8\ inch per minute during the determination of yield strength.
    (4) Each impact specimen must be Charpy V-notch type size 10 mm  x  
10 mm taken in accordance with paragraph 11 of ASTM Standard A-333-67. 
When a reduced size specimen is used, it must be the largest size 
obtainable.
    (k) Acceptable physical test results. Results of physical tests 
must conform to the following:
    (1) The tensile strength may not exceed 155,000 p.s.i.
    (2) The elongation must be at least 16 percent for a two-inch gage 
length.
    (3) The Charpy V-notch impact properties for the three impact 
specimens which must be tested at 0 deg. F may not be less than the 
values shown as follows:

------------------------------------------------------------------------
                                   Average value for   Minimum value (1 
      Size of specimen (mm)          acceptance (3     specimen only of 
                                      specimens)            the 3)      
------------------------------------------------------------------------
10.0  x  10.0...................  25.0 ft. lbs......  20.0 ft. lbs.     
10.0  x  7.5....................  21.0 ft. lbs......  17.0 ft. lbs.     
10.0  x  5.0....................  17.0 ft. lbs......  14.0 ft. lbs.     
------------------------------------------------------------------------

    (4) After the final heat treatment, each vessel must be hardness 
tested on the cylindrical section. The tensile strength equivalent of 
the hardness number obtained may not be more than 165,000 p.s.i. (Rc 
36). When the result of a hardness test exceeds the maximum permitted, 
two or more retests may be made; however, the hardness number obtained 
in each retest may not exceed the maximum permitted.
    (l) Rejected cylinders. Reheat treatment is authorized for rejected 
cylinders. However, each reheat treated cylinder must subsequently pass 
all the prescribed tests. Repair by welding is not authorized.
    (m) Markings. Marking must be done by stamping into the metal of 
the cylinder. All markings must be legible and located on a shoulder.
    (n) Inspector's report. In addition to the requirements of 
Sec. 178.35, the inspector's report for the physical test report, must 
indicate the average value for three specimens and the minimum value 
for one specimen for each lot number.


Sec. 178.46  Specification 3AL seamless aluminum cylinders.

    (a) Size and service pressure. A DOT 3AL cylinder is a seamless 
aluminum cylinder with a maximum water capacity of 1000 pounds and 
minimum service pressure of 150 psig.
    (b) Authorized material and identification of material. The 
material of construction must meet the following conditions:
    (1) Starting stock must be cast stock or traceable to cast stock.
    (2) Material with seams, cracks, laminations, or other defects 
likely to weaken the finished cylinder may not be used.
    (3) Material must be identified by a suitable method that will 
identify the alloy, the aluminum producer's cast number, the solution 
heat treat batch number and the lot number.
    (4) The material must be of uniform quality. Only the following 
heat treatable aluminum alloys in Tables 1 and 2 of this paragraph 
(b)(4) are permitted:

[[Page 8343]]


                                                        Table 1.--Chemical Composition Limits\1\                                                        
                                                       [Chemical composition (in weight percent)]                                                       
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                           Other \2\                    
    Aluminum Assoc. alloy          Si       Fe       Cu         Mn         Mg         Cr       Zn     Ti     Pb     Bi  --------------         Al       
       designation No.                                                                                                    Each  Total                   
--------------------------------------------------------------------------------------------------------------------------------------------------------
6351.........................    0.7-1.3   0.50       0.10  0.40-0.80  0.40-0.80  .........   0.20   0.20   0.01   0.01   0.05   0.15  Remainder.       
6061.........................  0.40-0.80    .70  0.15-0.40       0.15  0.80-1.20  0.04-0.35    .25    .15    .01    .01    .05    .15  Remainder.       
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ ASTM B 221-76 Standard Specification for Aluminum Alloy Extruded Bars, Rods, Shapes, and Tubes, Table 1 Chemical Composition Limits, Except for Pb  
  and Bi. Limits are in percent maximum unless otherwise indicated.                                                                                     
\2\ Analysis is regularly made only for the elements for which specific limits are shown, except for unalloyed aluminum. If however, the presence of    
  other elements is suspected to be, or in the course of routine analysis is indicated to be in excess of specified limits, further analysis is made to 
  determine that these other elements are not in excess of the amounts specified. (Aluminum Association Standards and Data/6th Edition, 1979).          


                                       Table 2--Mechanical Property Limits                                      
----------------------------------------------------------------------------------------------------------------
                                                                       Tensile strength--PSI       Elongation-- 
                                                                 --------------------------------     percent   
                        Alloy and temper                                                            minimum for 
                                                                    Ultimate--     Yield-minimum   2'' or 4D\1\ 
                                                                      minimum                      size specimen
----------------------------------------------------------------------------------------------------------------
6351-T6.........................................................          42,000          37,000          \2\ 14
6061-T6.........................................................          38,000          35,000          \2\ 14
----------------------------------------------------------------------------------------------------------------
\1\ ``D'' represents specimen diameters. When the cylinder wall is greater than \3/16\-inch thick, a retest     
  without reheat treatment using the 4D size specimen is authorized if the test using the 2 inch size specimen  
  fails to meet elongation requirements.                                                                        
\2\ When cylinder wall is not over \3/16\-inch thick, 10 percent elongation is authorized when using a 24t x 6t 
  size test specimen.                                                                                           

    (5) All starting stock must be 100 percent ultrasonically 
inspected, along the length at right angles to the central axis from 
two positions at 90 deg. to one another. The equipment and continuous 
scanning procedure must be capable of detecting and rejecting internal 
defects such as cracks which have an ultrasonic response greater than 
that of a calibration block with a \5/64\-inch diameter flat bottomed 
hole.
    (6) Cast stock must have uniform equiaxed grain structure not to 
exceed 500 microns maximum.
    (7) Any starting stock not complying with the above must be 
rejected.
    (c) Manufacture. Cylinders must be manufactured in accordance with 
the following requirements:
    (1) Cylinder shells must be manufactured by the backward extrusion 
method and have a cleanliness level adequate to ensure proper 
inspection. No fissure or other defect is acceptable that is likely to 
weaken the finished cylinder below the design strength requirements. A 
reasonably smooth and uniform surface finish is required. If not 
originally free from such defects, the surface may be machined or 
otherwise conditioned to eliminate these defects.
    (2) Thickness of the cylinder base may not be less than the 
prescribed minimum wall thickness of the cylindrical shell. The 
cylinder base must have a basic torispherical, hemispherical, or 
ellipsoidal interior base configuration where the dish radius is no 
greater than 1.2 times the inside diameter of the shell. The knuckle 
radius may not be less than 12 percent of the inside diameter of the 
shell. The interior base contour may deviate from the true 
torispherical, hemispherical or ellipsoidal configuration provided 
that--
    (i) Any areas of deviation are accompanied by an increase in base 
thickness;
    (ii) All radii of merging surfaces are equal to or greater than the 
knuckle radius;
    (iii) Each design has been qualified by successfully passing the 
cycling tests in paragraph (c) of this section; and
    (iv) Detailed specifications of the base design are available to 
the inspector.
    (3) For free standing cylinders, the base thickness must be at 
least two times the minimum wall thickness along the line of contact 
between the cylinder base and the floor when the cylinders are in the 
vertical position.
    (4) Welding or brazing is prohibited.
    (5) Each new design and any significant change to any acceptable 
design must be qualified for production by testing prototype samples as 
follows:
    (i) Three samples must be subjected to 100,000 pressure reversal 
cycles between zero and service pressure or 10,000 pressure reversal 
cycles between zero and test pressure, at a rate not in excess of 10 
cycles per minute without failure.
    (ii) Three samples must be pressurized to destruction and failure 
may not occur at less than 2.5 times the marked cylinder service 
pressure. Each cylinder must remain in one piece. Failure must initiate 
in the cylinder sidewall in a longitudinal direction. Rate of 
pressurization may not exceed 200 psi per second.
    (6) In this specification ``significant change'' means a 10 percent 
or greater change in cylinder wall thickness, service pressure, or 
diameter; a 30 percent or greater change in water capacity or base 
thickness; any change in material; over 100 percent increase in size of 
openings; or any change in the number of openings.
    (d) Wall thickness. The minimum wall thickness must be such that 
the wall stress at the minimum specified test pressure will not exceed 
80 percent of the minimum yield strength nor exceed 67 percent of the 
minimum ultimate tensile strength as verified by physical tests in 
paragraph (i) of this section. The minimum wall thickness for any 
cylinder with an outside diameter greater than 5 inches must be 0.125 
inch. Calculations must be made by the following formula:

S=[P(1.3D\2\+0.4d\2\)]/(D\2\-d\2\)

where:

S=Wall stress in pounds per square inch;
P=Prescribed minimum test pressure in pounds per square inch (see 
paragraph (g) of this section);
D=Outside diameter in inches; and
d=Inside diameter in inches.

    (e) Openings. Openings must comply with the following requirements:
    (1) Openings are permitted in heads only.
    
[[Page 8344]]

    (2) The size of any centered opening in a head may not exceed one-
half the outside diameter of the cylinder.
    (3) Other openings are permitted in the head of a cylinder if:
    (i) Each opening does not exceed 2.625 inches in diameter, or one-
half the outside diameter of the cylinder; whichever is less;
    (ii) Each opening is separated from each other by a ligament; and
    (iii) Each ligament which separates two openings must be at least 
three times the average of the diameters of the two openings.
    (4) All openings must be circular.
    (5) All openings must be threaded. Threads must comply with the 
following:
    (i) Each thread must be clean cut, even, without checks, and to 
gauge.
    (ii) Taper threads, when used, must conform to one of the 
following:
    (A) American Standard Pipe Thread (NPT) type, conforming to the 
requirements of Federal Standard H-28 (1978), Section 7;
    (B) National Gas Taper Thread (NGT) type, conforming to the 
requirements of Federal Standard H-28 (1978), Sections 7 and 9; or
    (C) Other taper threads conforming to other standards may be used 
provided the length is not less than that specified for NPT threads.
    (iii) Straight threads, when used, must conform to one of the 
following:
    (A) National Gas Straight Thread (NGS) type, conforming to the 
requirements of Federal Standard H-28, (1978), Sections 7 and 9;
    (B) Unified Thread (UN) type, conforming to the requirements of 
Federal Standard H-28, (1978), Section 2;
    (C) Controlled Radius Root Thread (UN) type, conforming to the 
requirements of Federal Standard H-28 (1978), Section 4; or
    (D) Other straight threads conforming to other recognized standards 
may be used provided that the requirements in paragraph (e)(5)(iv) of 
this section are met.
    (iv) All straight threads must have at least 6 engaged threads, a 
tight fit, and a factor of safety in shear of at least 10 at the test 
pressure of the cylinder. Shear stress must be calculated by using the 
appropriate thread shear area in accordance with Federal Standard H-28 
(1978), Appendix A5, Section 3.
    (f) Heat treatment. Prior to any test, all cylinders must be 
subjected to a solution heat treatment and aging treatment appropriate 
for the aluminum alloy used.
    (g) Hydrostatic test. Each cylinder must be subjected to an 
internal test pressure using the water jacket equipment and method or 
other suitable equipment and method and comply with the following 
requirements:
    (1) The testing apparatus must be operated in a manner so as to 
obtain accurate data. The pressure gauge used must permit reading to an 
accuracy of one percent. The expansion gauge must permit reading the 
total expansion to an accuracy of either one percent or 0.1 cubic 
centimeter.
    (2) The test pressure must be maintained for a sufficient period of 
time to assure complete expansion of the cylinder. In no case may the 
pressure be held less than 30 seconds. If, due to failure of the test 
apparatus, the required test pressure cannot be maintained, the test 
may be repeated at a pressure increased by 10 percent or 100 psi, 
whichever is lower. If the test apparatus again fails to maintain the 
test pressure, the cylinder being tested must be rejected. Any internal 
pressure applied to the cylinder before any official test may not 
exceed 90 percent of the test pressure.
    (3) The minimum test pressure is the greatest of the following:
    (i) 450 psi regardless of service pressure;
    (ii) Two times the service pressure for cylinders having service 
pressure less than 500 psi; or
    (iii) Five-thirds times the service pressure for cylinders having a 
service pressure of at least 500 psi.
    (4) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (h) Flattening test. One cylinder taken at random out of each lot 
must be subjected to a flattening test as follows:
    (1) The test must be between knife edges, wedge shaped, having a 
60 deg. included angle, and rounded in accordance with the following 
table. The longitudinal axis of the cylinder must be at an angle 
90 deg. to the knife edges during the test. The flattening test table 
is as follows:

                     Table 3.--Flattening Test Table                    
------------------------------------------------------------------------
                                                                 Radius 
               Cylinder wall thickness in inches                   in   
                                                                 inches 
------------------------------------------------------------------------
Under .150....................................................      .500
.150 to .249..................................................      .875
.250 to .349..................................................     1.500
.350 to .449..................................................     2.125
.450 to .549..................................................     2.750
.550 to .649..................................................     3.500
.650 to .749..................................................     4.125
------------------------------------------------------------------------

    (2) An alternate bend test in accordance with ASTM E 290-77 using a 
mandrel diameter not more than 6 times the wall thickness is authorized 
to qualify lots that fail the flattening test of this section without 
reheat treatment. If used, this test must be performed on two samples 
from one cylinder taken at random out of each lot of 200 cylinders or 
less.
    (3) Each test cylinder must withstand flattening to nine times the 
wall thickness without cracking. When the alternate bend test is used, 
the test specimens must remain uncracked when bent inward around a 
mandrel in the direction of curvature of the cylinder wall until the 
interior edges are at a distance apart not greater than the diameter of 
the mandrel.
    (i) Mechanical properties test. Two test specimens cut from one 
cylinder representing each lot of 200 cylinders or less must be 
subjected to the mechanical properties test, as follows:
    (1) The results of the test must conform to at least the minimum 
acceptable mechanical property limits for aluminum alloys as specified 
in paragraph (b) of this section.
    (2) Specimens must be 4D bar or gauge length 2 inches with width 
not over 1\1/2\ inch taken in the direction of extrusion approximately 
180 deg. from each other; provided that gauge length at least 24 times 
thickness with width not over 6 times thickness is authorized, when 
cylinder wall is not over \3/16\ inch thick. The specimen, exclusive of 
grip ends, may not be flattened. Grip ends may be flattened to within 
one inch of each end of the reduced section. When the size of the 
cylinder does not permit securing straight specimens, the specimens may 
be taken in any location or direction and may be straightened or 
flattened cold by pressure only, not by blows. When such specimens are 
used, the inspector's report must show that the specimens were so taken 
and prepared. Heating of specimens for any purpose is forbidden.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length.
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard B-557-79.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 

[[Page 8345]]
10,000,000 psi. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 6,000 psi, the 
strain indicator reading being set at the calculated corresponding 
strain.
    (iv) Cross-head speed of the testing machine may not exceed 1/8 
inch per minute during yield strength determination.
    (j) Rejected cylinder. Reheat treatment of rejected cylinders is 
authorized one time. Subsequent thereto, cylinders must pass all 
prescribed tests to be acceptable.
    (k) Duties of inspector. In addition to the requirements of 
Sec. 178.35, the inspector shall:
    (1) Verify compliance with the provisions of paragraph (b) of this 
section by:
    (i) Performing or witnessing the performance of the chemical 
analyses on each melt or cast lot or other unit of starting material; 
or
    (ii) Obtaining a certified chemical analysis from the material or 
cylinder manufacturer for each melt, or cast of material; or
    (iii) Obtaining a certified check analysis on one cylinder out of 
each lot of 200 cylinders or less, if a certificate containing data to 
indicate compliance with the material specification is obtained.
    (2) The inspector shall verify ultrasonic inspection of all 
material by inspection or by obtaining the material producer's 
certificate of ultrasonic inspection. Ultrasonic inspection must be 
performed or verified as having been performed in accordance with 
paragraph (c) of this section.
    (3) The inspector must also determine that each cylinder complies 
with this specification by:
    (i) Selecting the samples for check analyses performed by other 
than the material producer;
    (ii) Verifying that the prescribed minimum thickness was met by 
measuring or witnessing the measurement of the wall thickness; and
    (iii) Verifying that the identification of material is proper.
    (4) Prior to initial production of any design or design change, 
verify that the design qualification tests prescribed in paragraph 
(c)(6) of this section have been performed with acceptable results.
    (l) Definitions. In this specification, a ``lot'' means of group of 
cylinders successively produced having the same:
    (i) Size and configuration;
    (ii) Specified material of construction;
    (iii) Process of manufacture and heat treatment;
    (iv) Equipment of manufacture and heat treatment; and
    (v) Conditions of time, temperature and atmosphere during heat 
treatment. In no case may the lot size exceed 200 cylinders, but any 
cylinder processed for use in the required destructive physical testing 
need not be counted as being one of the 200.
    (m) Inspector's report. In addition to the information required by 
Sec. 178.35, the record of chemical analyses must also include the 
alloy designation, and applicable information on iron, titanium, zinc, 
magnesium and any other applicable element used in the construction of 
the cylinder.


Sec. 178.47  Specification 4DS welded stainless steel cylinders for 
aircraft use.

    (a) Type, size, and service pressure. A DOT 4DS cylinder is either 
a welded stainless steel sphere (two seamless hemispheres) or 
circumferentially welded cylinder both with a water capacity of not 
over 100 pounds and a service pressure of at least 500 but not over 900 
pounds per square inch.
    (b) Steel. Types 304, 321 and 347 stainless steel are authorized 
with proper welding procedure. A heat of steel made under the 
specifications in Table 1 of this paragraph (b), check chemical 
analysis of which is slightly out of the specified range, is 
acceptable, if satisfactory in all other respects, provided the 
tolerances shown in Table 2 of this paragraph (b) are not exceeded, 
except as approved by Associate Administrator. The following chemical 
analyses are authorized:

                                         Table 1.--Authorized Materials                                         
----------------------------------------------------------------------------------------------------------------
                                                                     Stainless steels                           
                                        ------------------------------------------------------------------------
                                              304  (percent)          321  (percent)          347  (percent)    
----------------------------------------------------------------------------------------------------------------
Carbon (max)...........................  0.08                     0.08                    0.08                  
Manganese (max)........................  2.00                     2.00                    2.00                  
Phosphorus\1\ (max)....................  .030                     .030                    .030                  
Sulphur (max)..........................  .030                     .030                    .030                  
Silicon (max)..........................  .75                      .75                     .75                   
Nickel.................................  8.0/11.0                 9.0/13.0                9.0/13.0              
Chromium...............................  18.0/20.0                17.0/20.0               17.0/20.0             
Molybdenum.............................  .......................  ......................  ......................
Titanium...............................  .......................  (\1\)                                         
Columbium..............................  .......................  ......................  (\2\)                 
----------------------------------------------------------------------------------------------------------------
\1\ Titanium may not be than 5C and not more than 0.60%.                                                        
\2\ Columbium may not be less than 10C and not more than 1.0%.                                                  


                                       Table 2.--Check Analysis Tolerances                                      
----------------------------------------------------------------------------------------------------------------
                                                                                   Tolerance (percent) over the 
                                                                                    maximum limit or under the  
                                                  Limit or maximum specified               minimum limit        
                  Element                                 (percent)              -------------------------------
                                                                                   Under minimum   Over maximum 
                                                                                       limit           limit    
----------------------------------------------------------------------------------------------------------------
Carbon.....................................  To 0.15 incl.......................            0.01            0.01
Manganese..................................  Over 1.15 to 2.50 incl.............             .05             .05
Phosphorus\1\..............................  All ranges.........................  ..............             .01
Sulphur....................................  All ranges.........................  ..............             .01

[[Page 8346]]
                                                                                                                
Silicon....................................  Over 0.30 to 1.00 incl.............             .05             .05
Nickel.....................................  Over 5.30 to 10.00 incl............             .10             .10
                                             Over 10.00 to 14.00 incl...........             .15             .15
Chromium...................................  Over 15.00 to 20.00 incl...........             .20             .20
Titanium...................................  All ranges.........................             .05             .05
Columbium..................................  All ranges.........................             .05             .05
----------------------------------------------------------------------------------------------------------------
\1\ Rephosphorized steels not subject to check analysis for phosphorus.                                         


    (c) Identification of material. Materials must be identified by any 
suitable method.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is permitted that is likely 
to weaken the finished cylinder appreciably; a reasonably smooth and 
uniform surface finish is required. No abrupt change in wall thickness 
is permitted. Welding procedures and operators must be qualified in 
accordance with CGA Pamphlet C-3. All seams of the sphere or cylinder 
must be fusion welded. Seams must be of the butt type and means must be 
provided for accomplishing complete penetration of the joint.
    (e) Attachments. Attachments to the container are authorized by 
fusion welding provided that such attachments are made of weldable 
stainless steel in accordance with paragraph (b) of this section.
    (f) Wall thickness. The minimum wall thickness must be such that 
the wall stress at the minimum specified test pressure may not be over 
60,000 psi. A minimum wall thickness of 0.040 inch is required for any 
diameter container. Calculations must be made by the following 
formulas:
    (1) Calculation for sphere must be made by the formula:

S=PD/4tE

where:

S=Wall stress in pounds per square inch;
P=Test pressure prescribed for water jacket test, i.e., at least two 
times service pressure, in pounds per square inch;
D=Outside diameter in inches;
t=Minimum wall thickness in inches;
E=0.85 (provides 85 percent weld efficiency factor which must be 
applied in the girth weld area and heat zones which zone must extend a 
distance of 6 times wall thickness from center of weld);
E=1.0 (for all other areas).

    (2) Calculation for a cylinder must be made by the formula:

S=[P(1.3D\2\+0.4d\2\)]/(D\2\-d\2\)

where:

S=Wall stress in pounds per square inch;
P=Test pressure prescribed for water jacket test, i.e., at least two 
times service pressure, in pounds per square inch;
D=Outside diameter in inches;
d=Inside diameter in inches.

    (g) Heat treatment. The seamless hemispheres and cylinders may be 
stress relieved or annealed for forming. Welded container must be 
stress relieved at a temperature of 775  deg.F 25 deg. 
after process treatment and before hydrostatic test.
    (h) Openings in container. Openings must comply with the following:
    (1) Each opening in the container must be provided with a fitting, 
boss or pad of weldable stainless steel securely attached to the 
container by fusion welding.
    (2) Attachments to a fitting, boss, or pad must be adequate to 
prevent leakage. Threads must comply with the following:
    (i) Threads must be clean cut, even, without checks, and tapped to 
gauge.
    (ii) Taper threads to be of length not less than as specified for 
American Standard taper pipe threads.
    (iii) Straight threads having at least 4 engaged threads, to have 
tight fit and calculated shear strength at least 10 times the test 
pressure of the container; gaskets required, adequate to prevent 
leakage.
    (i) Process treatment. Each container must be hydraulically 
pressurized in a water jacket to at least 100 percent, but not more 
than 110 percent, of the test pressure and maintained at this pressure 
for a minimum of 3 minutes. Total and permanent expansion must be 
recorded and included in the inspector's report.
    (j) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test as follows:
    (1) The test must be by water-jacket, operated so as to obtain 
accurate data. The pressure gauge must permit reading to an accuracy of 
1 percent. The expansion gauge must permit reading of total expansion 
to an accuracy either of 1 percent or 0.1 cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. If, due to failure of 
the test apparatus, the test pressure cannot be maintained, the test 
may be repeated at a pressure increased by 10 percent or 100 pounds per 
square inch, whichever is the lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) Each container must be tested to at least 2 times service 
pressure.
    (5) Container must then be inspected. Any wall thickness lower than 
that required by paragraph (f) of this section must be cause for 
rejection. Bulges and cracks must be cause for rejection. Welded joint 
defects exceeding requirements of paragraph (k) of this section must be 
cause for rejection.
    (k) Radiographic inspection. Radiographic inspection is required on 
all welded joints which are subjected to internal pressure, except that 
at the discretion of the disinterested inspector, openings less than 25 
percent of the container diameter need not be subjected to radiographic 
inspection. Evidence of any defects likely to seriously weaken the 
container is cause for rejection. Radiographic inspection must be 
performed subsequent to the hydrostatic test.
    (l) Burst test. One container taken at random out of 200 or less 
must be hydrostatically tested to destruction. Rupture pressure must be 
included as part of the inspector's report.
    (m) Flattening test. A flattening test must be performed as 
follows: 

[[Page 8347]]

    (1) For spheres the test must be at the weld between parallel steel 
plates on a press with welded seam at right angles to the plates. Test 
one sphere taken at random out of each lot of 200 or less after the 
hydrostatic test. Any projecting appurtenances may be cut off (by 
mechanical means only) prior to crushing.
    (2) For cylinders the test must be between knife edges, wedge 
shaped, 60 deg. angle, rounded to \1/2\-inch radius. Test one cylinder 
taken at random out of each lot of 200 or less, after the hydrostatic 
test.
    (n) Acceptable results for flattening and burst tests. Acceptable 
results for flattening and burst tests are as follows:
    (1) Flattening required to 50 percent of the original outside 
diameter without cracking.
    (2) Burst pressure must be at least 3 times the service pressure.
    (o) Rejected containers. Repair of welded seams by welding prior to 
process treatment is authorized. Subsequent thereto, containers must be 
heat treated and pass all prescribed tests.
    (p) Duties of inspector. In addition to the requirements of 
Sec. 178.35, the inspector must verify that all tests are conducted at 
temperatures between 60 deg. F and 90 deg. F.
    (q) Marking. Markings must be stamped plainly and permanently on a 
permanent attachment or on a metal nameplate permanently secured to the 
container by means other than soft solder.
    Sec. 178.50 Specification 4B welded or brazed steel cylinders.
    (a) Type, size, and service pressure. A DOT 4B is a welded or 
brazed steel cylinder with longitudinal seams that are forged lap-
welded or brazed and with water capacity (nominal) not over 1,000 
pounds and a service pressure of at least 150 but not over 500 pounds 
per square inch. Cylinders closed in by spinning process are not 
authorized.
    (b) Steel. Open-hearth, electric or basic oxygen process steel of 
uniform quality must be used. Content percent may not exceed the 
following: Carbon, 0.25; phosphorus, 0.045; sulphur, 0.050.
    (c) Identification of material. Material must be identified by any 
suitable method except that plates and billets for hotdrawn cylinders 
must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is permitted that is likely 
to weaken the finished cylinder appreciably. A reasonably smooth and 
uniform surface finish is required. Exposed bottom welds on cylinders 
over 18 inch long must be protected by footrings. Welding procedures 
and operators must be qualified in accordance with CGA Pamphlet C-3. 
Seams must be made as follows:
    (1) Welded or brazed circumferential seams. Heads attached by 
brazing must have a driving fit with the shell, unless the shell is 
crimped, swedged, or curled over the skirt or flange of the head, and 
be thoroughly brazed until complete penetration by the brazing material 
of the brazed joint is secured. Depth of brazing from end of shell must 
be at least four times the thickness of shell metal.
    (2) Longitudinal seams in shells. Longitudinal seams must be forged 
lap welded, by copper brazing, by copper alloy brazing, or by silver 
alloy brazing. Copper alloy composition must be: Copper, 95 percent 
minimum; Silicon, 1.5 percent to 3.85 percent; Manganese, 0.25 percent 
to 1.10 percent. The melting point of the silver alloy brazing material 
must be in excess of 1000 deg. F. When brazed, the plate edge must be 
lapped at least eight times the thickness of plate, laps being held in 
position, substantially metal to metal, by riveting or electric spot-
welding; brazing must be done by using a suitable flux and by placing 
brazing material on one side of seam and applying heat until this 
material shows uniformly along the seam of the other side.
    (e) Welding or brazing. Only the attachment of neckrings, 
footrings, handles, bosses, pads, and valve protection rings to the 
tops and bottoms of cylinders by welding or brazing is authorized. Such 
attachments and the portion of the container to which they are attached 
must be made of weldable steel, the carbon content of which may not 
exceed 0.25 percent except in the case of 4130X steel which may be used 
with proper welding procedure.
    (f) Wall thickness. The wall thickness of the cylinder must comply 
with the following requirements:
    (1) For cylinders with outside diameters over 6 inches the minimum 
wall thickness must be 0.090 inch. In any case, the minimum wall 
thickness must be such that calculated wall stress at minimum test 
pressure (paragraph (i)(4) of this section) may not exceed the 
following values:
    (i) 24,000 pounds per square inch for cylinders without 
longitudinal seam.
    (ii) 22,800 pounds per square inch for cylinders having copper 
brazed or silver alloy brazed longitudinal seam.
    (iii) 18,000 pounds per square inch for cylinders having forged 
lapped welded longitudinal seam.
    (2) Calculation must be made by the formula:

S=[P(1.3D\2\+0.4d\2\)]/(D\2\-d\2\)

where:

S=wall stress in pounds per square inch;
P=minimum test pressure prescribed for water jacket test or 450 pounds 
per square inch whichever is the greater;
D=outside diameter in inches;
d=inside diameter in inches.
    (g) Heat treatment. Cylinder body and heads, formed by drawing or 
pressing, must be uniformly and properly heat treated prior to tests.
    (h) Opening in cylinders. Openings in cylinders must conform to the 
following:
    (1) Each opening in cylinders, except those for safety devices, 
must be provided with a fitting, boss, or pad, securely attached to 
cylinder by brazing or by welding or by threads. Fitting, boss, or pad 
must be of steel suitable for the method of attachment employed, and 
which need not be identified or verified as to analysis except that if 
attachment is by welding, carbon content may not exceed 0.25 percent. 
If threads are used, they must comply with the following:
    (i) Threads must be clean cut, even without checks, and tapped to 
gauge.
    (ii) Taper threads to be of length not less than as specified for 
American Standard taper pipe threads.
    (iii) Straight threads, having at least 4 engaged threads, to have 
tight fit and calculated shear strength at least 10 times the test 
pressure of the cylinder; gaskets required, adequate to prevent 
leakage.
    (iv) A brass fitting may be brazed to the steel boss or flange on 
cylinders used as component parts of hand fire extinguishers.
    (2) The closure of a fitting, boss, or pad must be adequate to 
prevent leakage.
    (i) Hydrostatic test. Each cylinder must withstand a hydrostatic 
test as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy either of 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the test pressure. If, due to failure of the test 
apparatus, the test pressure cannot be 

[[Page 8348]]
maintained, the test may be repeated at a pressure increased by 10 
percent or 100 pounds per square inch, whichever is the lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) Cylinders must be tested as follows:
    (i) At least one cylinder selected at random out of each lot of 200 
or less must be tested as outlined in paragraphs (i)(1), (i)(2), and 
(i)(3) of this section to at least two times service pressure.
    (ii) All cylinders not tested as outlined in paragraph (i)(4)(i) of 
this section must be examined under pressure of at least two times 
service pressure and show no defect.
    (j) Flattening test. After the hydrostatic test, a flattening test 
must be performed on one cylinder taken at random out or each lot of 
200 or less, by placing the cylinder between wedge shaped knife edges 
having a 60 deg. included angle, rounded to \1/2\-inch radius. The 
longitudinal axis of the cylinder must be at a 90-degree angle to knife 
edges during the test. For lots of 30 or less, flattening tests are 
authorized to be made on a ring at least 8 inches long cut from each 
cylinder and subjected to same heat treatment as the finished cylinder.
    (k) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material as follows:
    (1) The test is required on 2 specimens cut from 1 cylinder, or 
part thereof heat-treated as required, taken at random out of each lot 
of 200 or less. For lots of 30 or less, physical tests are authorized 
to be made on a ring at least 8 inches long cut from each cylinder and 
subjected to same heat treatment as the finished cylinder.
    (2) Specimens must conform to the following:
    (i) A gauge length of 8 inches with a width of not over 1\1/2\ 
inches, a gauge length of 2 inches with a width of not over 1\1/2\ 
inches, or a gauge length at least 24 times the thickness with a width 
not over 6 times the thickness is authorized when a cylinder wall is 
not over \3/16\ inch thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within one inch of each end of the 
reduced section.
    (iii) When size of cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold, by pressure only, not by blows. 
When specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch, and strain indicator reading must be set at the calculated 
corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (l) Acceptable results for physical and flattening tests. Either of 
the following is an acceptable result:
    (1) An elongation of at least 40 percent for a 2 inch gauge length 
or at least 20 percent in other cases and yield strength not over 73 
percent of tensile strength. In this instance, a flattening test is not 
required.
    (2) When cylinders are constructed of lap welded pipe, flattening 
test is required, without cracking, to 6 times the wall thickness. In 
such case, the rings (crop ends) cut from each end of pipe, must be 
tested with the weld 45 deg. or less from the point of greatest stress. 
If a ring fails, another from the same end of pipe may be tested.
    (m) Rejected cylinders. Reheat treatment is authorized for rejected 
cylinder. Subsequent thereto, cylinders must pass all prescribed tests 
to be acceptable. Repair of brazed seams by brazing and welded seams by 
welding is authorized.
    (n) Markings. Markings must be stamped plainly and permanently in 
any of the following locations on the cylinder:
    (1) On shoulders and top heads when they are not less than 0.087-
inch thick.
    (2) On side wall adjacent to top head for side walls which are not 
less than 0.090 inch thick.
    (3) On a cylindrical portion of the shell which extends beyond the 
recessed bottom of the cylinder, constituting an integral and non-
pressure part of the cylinder.
    (4) On a metal plate attached to the top of the cylinder or 
permanent part thereof; sufficient space must be left on the plate to 
provide for stamping at least six retest dates; the plate must be at 
least \1/16\ inch thick and must be attached by welding, or by brazing. 
The brazing rod must melt at a temperature of 1100  deg.F. Welding or 
brazing must be along all the edges of the plate.
    (5) On the neck, neckring, valve boss, valve protection sleeve, or 
similar part permanently attached to the top of the cylinder.
    (6) On the footring permanently attached to the cylinder, provided 
the water capacity of the cylinder does not exceed 25 pounds.


Sec. 178.51  Specification 4BA welded or brazed steel cylinders.

    (a) Type, size, and service pressure. A DOT 4BA cylinder is a 
cylinder, either spherical or cylindrical in shape, with a water 
capacity of 1,000 pounds or less and a service pressure of at least 225 
and not over 500 pounds per square inch. Closures made by the spinning 
process are not authorized.
    (1) Spherical type cylinders must be made from two seamless 
hemispheres joined by the welding of one circumferential seam.
    (2) Cylindrical type cylinders must be of circumferentially welded 
or brazed construction.
    (b) Steel. The steel used in the construction of the cylinder must 
be as specified in Table 1 of Appendix A to this part.
    (c) Identification of material. Material must be identified by any 
suitable method except that plates and billets for hotdrawn cylinders 
must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is permitted that is likely 
to weaken the finished cylinder appreciably. A reasonably smooth and 
uniform surface finish is required. Exposed bottom welds on cylinders 
over 18 inches long must be protected by footrings.
    (1) Seams must be made as follows:
    (i) Minimum thickness of heads and bottoms must be not less than 90 


[[Page 8349]]
percent of the required thickness of the side wall.
    (ii) Circumferential seams must be made by welding or by brazing. 
Heads must be attached by brazing and must have a driving fit with the 
shell, unless the shell is crimped, swedged or curled over the skirt or 
flange of the head and must be thoroughly brazed until complete 
penetration by the brazing material of the brazed joint is secured. 
Depth of brazing from end of the shell must be at least four times the 
thickness of shell metal.
    (iii) Longitudinal seams in shells must be made by copper brazing, 
copper alloy brazing, or by silver alloy brazing. Copper alloy 
composition must be: Copper 95 percent minimum, Silicon 1.5 percent to 
3.85 percent, Manganese 0.25 percent to 1.10 percent. The melting point 
of the silver alloy brazing material must be in excess of 1,000  deg.F. 
The plate edge must be lapped at least eight times the thickness of 
plate, laps being held in position, substantially metal to metal, by 
riveting or by electric spot-welding. Brazing must be done by using a 
suitable flux and by placing brazing material on one side of seam and 
applying heat until this material shows uniformly along the seam of the 
other side. Strength of longitudinal seam: Copper brazed longitudinal 
seam must have strength at least \3/2\ times the strength of the steel 
wall.
    (2) Welding procedures and operators must be qualified in 
accordance with CGA Pamphlet C-3.
    (e) Welding and brazing. Only the welding or brazing of neckrings, 
footrings, handles, bosses, pads, and valve protection rings to the 
tops and bottoms of cylinders is authorized. Provided that such 
attachments and the portion of the container to which they are attached 
are made of weldable steel, the carbon content of which may not exceed 
0.25 percent except in the case of 4130X steel which may be used with 
proper welding procedures.
    (f) Wall thickness. The minimum wall thickness of the cylinder must 
meet the following conditions:
    (1) For any cylinder with an outside diameter of greater than 6 
inches, the minimum wall thickness is 0.078 inch. In any case the 
minimum wall thickness must be such that the calculated wall stress at 
the minimum test pressure may not exceed the lesser value of any of the 
following:
    (i) The value shown in Table I of Appendix A to this part, for the 
particular material under consideration;
    (ii) One-half of the minimum tensile strength of the material 
determined as required in paragraph (j) of this section;
    (iii) 35,000 pounds per square inch; or
    (iv) Further provided that wall stress for cylinders having copper 
brazed longitudinal seams may not exceed 95 percent of any of the above 
values. Measured wall thickness may not include galvanizing or other 
protective coating.
    (2) Cylinders that are cylindrical in shape must have the wall 
stress calculated by the formula:

S=[P(1.3D2+0.4d2)]/(D2-d2)
where:

S=wall stress in pounds per square inch;
P=minimum test pressure prescribed for water jacket test;
D=outside diameter in inches;
d=inside diameter in inches.

    (3) Cylinders that are spherical in shape must have the wall stress 
calculated by the formula:

S=PD/4tE

where:

S=wall stress in pounds per square inch;
P=minimum test pressure prescribed for water jacket test;
D=outside diameter in inches;
t=minimum wall thickness in inches;
E=0.85 (provides 85 percent weld efficiency factor which must be 
applied in the girth weld area and heat affected zones which zone must 
extend a distance of 6 times wall thickness from center line of weld);
E=1.0 (for all other areas).

    (4) For a cylinder with a wall thickness less than 0.100 inch, the 
ratio of tangential length to outside diameter may not exceed 4.1.
    (g) Heat treatment. Cylinders must be heat treated in accordance 
with the following requirements:
    (1) Each cylinder must be uniformly and properly heat treated prior 
to test by the applicable method shown in Table I of Appendix A to this 
Part. Heat treatment must be accomplished after all forming and welding 
operations, except that when brazed joints are used, heat treatment 
must follow any forming and welding operations, but may be done before, 
during or after the brazing operations.
    (2) Heat treatment is not required after the welding or brazing of 
weldable low carbon parts to attachments of similar material which have 
been previously welded or brazed to the top or bottom of cylinders and 
properly heat treated, provided such subsequent welding or brazing does 
not produce a temperature in excess of 400  deg.F in any part of the 
top or bottom material.
    (h) Openings in cylinders. Openings in cylinders must comply with 
the following requirements:
    (1) Any opening must be placed on other than a cylindrical surface.
    (2) Each opening in a spherical type cylinder must be provided with 
a fitting, boss, or pad of weldable steel securely attached to the 
container by fusion welding.
    (3) Each opening in a cylindrical type cylinder must be provided 
with a fitting, boss, or pad, securely attached to container by brazing 
or by welding.
    (4) If threads are used, they must comply with the following:
    (i) Threads must be clean-cut, even, without checks and tapped to 
gauge.
    (ii) Taper threads must be of a length not less than that specified 
for American Standard taper pipe threads.
    (iii) Straight threads, having at least 4 engaged threads, must 
have a tight fit and a calculated shear strength of at least 10 times 
the test pressure of the cylinder. Gaskets, adequate to prevent 
leakage, are required.
    (i) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test, as follows:
    (1) The test must be by water jacket, or other suitable method, 
operated so as to obtain accurate data. A pressure gauge must permit 
reading to an accuracy of 1 percent. An expansion gauge must permit 
reading of total expansion to an accuracy of either 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat treatment and previous to the official test may not 
exceed 90 percent of the test pressure.
    (3) Permanent volumetric expansion may not exceed 10 percent of the 
total volumetric expansion at test pressure.
    (4) Cylinders must be tested as follows:
    (i) At least one cylinder selected at random out of each lot of 200 
or less must be tested as outlined in paragraphs (i)(1), (i)(2), and 
(i)(3) of this section to at least two times service pressure.
    (ii) All cylinders not tested as outlined in paragraph (i)(4)(i) of 
this section must be examined under pressure of at least two times 
service pressure and show no defect.
    (j) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material, as follows:
    (1) The test is required on 2 specimens cut from one cylinder or 
part thereof having passed the hydrostatic test and heat-treated as 
required, taken at random out of each lot of 200 or less. Physical 
tests for spheres are required on 2 specimens cut from flat 
representative sample plates of the same heat taken at random from the 
steel used 

[[Page 8350]]
to produce the spheres. This flat steel from which 2 specimens are to 
be cut must receive the same heat treatment as the spheres themselves. 
Sample plates must be taken from each lot of 200 or less spheres.
    (2) Specimens must conform to the following:
    (i) A gauge length of 8 inches with a width not over 1\1/2\ inches, 
or a gauge length of 2 inches with a width not over 1\1/2\ inches, or a 
gauge length at least 24 times the thickness with a width not over 6 
times the thickness is authorized when a cylinder wall is not over \3/
16\ inch thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within one inch of each end of the 
reduced section.
    (iii) When size of the cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold, by pressure only, not by blows. 
When specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load''), corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
reference must be set while the specimen is under a stress of 12,000 
pounds per square inch, and the strain indicator reading must be set at 
the calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed 1/8 
inch per minute during yield strength determination.
    (k) Elongation. Physical test specimens must show at least a 40 
percent elongation for a 2-inch gauge length or at least 20 percent in 
other cases. Except that these elongation percentages may be reduced 
numerically by 2 for 2-inch specimens, and by 1 in other cases, for 
each 7,500 pounds per square inch increment of tensile strength above 
50,000 pounds per square inch to a maximum of four such increments.
    (l) Tests of welds. Except for brazed seams, welds must be tested 
as follows:
    (1) Tensile test. A specimen must be cut from one cylinder of each 
lot of 200 or less, or welded test plate. The welded test plate must be 
of one of the heats in the lot of 200 or less which it represents, in 
the same condition and approximately the same thickness as the cylinder 
wall except that in no case must it be of a lesser thickness than that 
required for a quarter size Charpy impact specimen. The weld must be 
made by the same procedures and subjected to the same heat treatment as 
the major weld on the cylinder. The specimen must be taken from across 
the major seam and must be prepared and tested in accordance with and 
must meet the requirements of CGA Pamphlet C-3. Should this specimen 
fail to meet the requirements, specimens may be taken from two 
additional cylinders or welded test plates from the same lot and 
tested. If either of the latter specimens fail to meet the 
requirements, the entire lot represented must be rejected.
    (2) Guided bend test. A root bend test specimen must be cut from 
the cylinder or welded test plate, used for the tensile test specified 
in paragraph (l)(1) of this section. Specimens must be taken from 
across the major seam and must be prepared and tested in accordance 
with and must meet the requirements of CGA Pamphlet C-3.
    (3) Alternate guided-bend test. This test may be used and must be 
as required by CGA Pamphlet C-3. The specimen must be bent until the 
elongation at the outer surface, adjacent to the root of the weld, 
between the lightly scribed gage lines a to b, must be at least 20 
percent, except that this percentage may be reduced for steels having a 
tensile strength in excess of 50,000 pounds per square inch, as 
provided in paragraph (k) of this section.
    (m) Rejected cylinders. Reheat treatment is authorized for rejected 
cylinders. Subsequent thereto, cylinders must pass all prescribed tests 
to be acceptable. Repair of brazed seams by brazing and welded seams by 
welding is authorized.
    (n) Markings. Markings must be stamped plainly and permanently in 
one of the following locations on the cylinder:
    (1) On shoulders and top heads not less than 0.087 inch thick.
    (2) On side wall adjacent to top head for side walls not less than 
0.090 inch thick.
    (3) On a cylindrical portion of the shell which extends beyond the 
recessed bottom of the cylinder constituting an integral and non-
pressure part of the cylinder.
    (4) On a plate attached to the top of the cylinder or permanent 
part thereof; sufficient space must be left on the plate to provide for 
stamping at least six retest dates; the plate must be at least \1/16\ 
inch thick and must be attached by welding, or by brazing at a 
temperature of at least 1100 deg. F., throughout all edges of the 
plate.
    (5) On the neck, neckring, valve boss, valve protection sleeve, or 
similar part permanently attached to the top of the cylinder.
    (6) On the footring permanently attached to the cylinder, provided 
the water capacity of the cylinder does not exceed 25 pounds.


Sec. 178.53  Specification 4D welded steel cylinders for aircraft use.

    (a) Type, size, and service pressure. A DOT 4D cylinder is a welded 
steel sphere (two seamless hemispheres) or circumferentially welded 
cylinder (two seamless drawn shells) with a water capacity not over 100 
pounds and a service pressure of at least 300 but not over 500 pounds 
per square inch. Cylinders closed in by spinning process are not 
authorized.
    (b) Steel. Open-hearth or electric steel of uniform and weldable 
quality must be used. Content may not exceed the following: Carbon, 
0.25; phosphorus, 0.045; sulphur, 0.050, except that the following 
steels commercially known as 4130X and Type 304, 316, 321, and 347 
stainless steels may be used with proper welding procedure. A heat of 
steel made under Table 1 of this paragraph (b), check chemical analysis 
of which is slightly out of the specified range, is acceptable, if 
satisfactory in all other respects, provided the tolerances shown in 
Table 2 of this paragraph (b) are not exceeded, except as approved by 
the Associate Administrator. The following chemical analyses are 
authorized: 

[[Page 8351]]


                          Table 1.--4130X Steel                         
------------------------------------------------------------------------
                     4130X                               Percent        
------------------------------------------------------------------------
Carbon.........................................  0.25/0.35.             
Manganese......................................  0.40/0.60.             
Phosphorus.....................................  0.04 max.              
Sulphur........................................  0.05 max.              
Silicon........................................  0.15/0.35.             
Chromium.......................................  0.80/1.10.             
Molybdenum.....................................  0.15/0.25.             
Zirconium......................................  None.                  
Nickel.........................................  None.                  
------------------------------------------------------------------------


                                      Table 2.--Authorized Stainless Steels                                     
----------------------------------------------------------------------------------------------------------------
                                                                Stainless steels                                
                              ----------------------------------------------------------------------------------
                                                                                                        347     
                                   304 (percent)          316 (percent)          321 (percent)       (percent)  
----------------------------------------------------------------------------------------------------------------
Carbon (max).................  0.08.................  0.08.................  0.08................  0.08         
Manganese (max)..............  2.00.................  2.00.................  2.00................  2.00         
Phosphorus1 (max)............  .030.................  .045.................  .030................  .030         
Sulphur (max)................  .030.................  .030.................  .030................  .030         
Silicon (max)................  .75..................  1.00.................  .75.................  .75          
Nickel.......................  8.0/11.0.............  10.0/14.0............  9.0/13.0............  9.0/13.0     
Chromium.....................  18.0/20.0............  16.0/18.0............  17.0/20.0...........  17.0/20.0    
Molybdenum...................  .....................  2.0/3.0..............  ....................  .............
Titanium.....................  .....................  .....................  (\1\)...............  .............
Columbium....................  .....................  .....................  ....................  (\2\)        
----------------------------------------------------------------------------------------------------------------
\1\ Titanium may not be less than 5C and not more than 0.60%.                                                   
\2\ Columbium may not be less than 10C and not more than 1.0%.                                                  


                                       Table 3.--Check Analysis Tolerances                                      
----------------------------------------------------------------------------------------------------------------
                                                                                       Tolerance (percent) over 
                                                                                      the maximum limit or under
                                                                                           the minimum limit    
              Element                     Limit or maximum specified  (percent)      ---------------------------
                                                                                          Under                 
                                                                                         minimum    Over maximum
                                                                                          limit         limit   
----------------------------------------------------------------------------------------------------------------
Carbon.............................  To 0.15 incl...................................          0.01          0.01
                                     Over 0.15 to 0.40 incl.........................           .03           .04
Manganese..........................  To 0.60 incl...................................           .03           .03
                                     Over 1.15 to 2.50 incl.........................           .05           .05
Phosphorus\1\......................  All ranges.....................................  ............           .01
Sulphur............................  All ranges.....................................  ............           .01
Silicon............................  To 0.30 incl...................................           .02           .03
                                     Over 0.30 to 1.00 incl.........................           .05           .05
Nickel.............................  Over 5.30 to 10.00 incl........................           .10           .10
                                     Over 10.00 to 14.00 incl.......................           .15           .15
Chromium...........................  To 0.90 incl...................................           .03           .03
                                     Over 0.90 to 2.10 incl.........................           .05           .05
                                     Over 15.00 to 20.00 incl.......................           .20           .20
Molybdenum.........................  To 0.20 incl...................................           .01           .01
                                     Over 0.20 to 0.40 incl.........................           .02           .02
                                     Over 1.75 to 3.0 incl..........................           .10           .10
Titanium...........................  All ranges.....................................           .05           .05
Columbium..........................  All ranges.....................................           .05           .05
----------------------------------------------------------------------------------------------------------------
\1\ Rephosphorized steels not subject to check analysis for phosphorus.                                         

    (c) Identification of material. Material must be identified by any 
suitable method except that plates and billets for hotdrawn cylinders 
must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is permitted that is likely 
to weaken the finished container appreciably. A reasonably smooth and 
uniform surface finish is required. Welding procedures and operators 
must be qualified in accordance with CGA Pamphlet C-3.
    (e) Wall thickness. The wall stress at the minimum test pressure 
may not exceed 24,000 pounds per square inch, except where steels 
commercially known as 4130X, types 304, 316, 321, and 347 stainless 
steels are used, stress at the test pressures may not exceed 37,000 
pounds per square inch. The minimum wall thickness for any container 
having a capacity of 1,100 cubic inches or less is 0.04 inch. The 

[[Page 8352]]
minimum wall thickness for any container having a capacity in excess of 
1,100 cubic inches is 0.095 inch. Calculations must be done by the 
following:
    (1) Calculation for a ``sphere'' must be made by the formula:

S=PD/4tE

Where:
S=wall stress in pounds per square inch;
P=test pressure prescribed for water jacket test, i.e., at least two 
times service pressure, in pounds per square inch;
D=outside diameter in inches;
t=minimum wall thickness in inches;
E=0.85 (provides 85 percent weld efficiency factor which must be 
applied in the girth weld area and heat affected zones which zone must 
extend a distance of 6 times wall thickness from center line of weld);
E=1.0 (for all other areas).

    (2) Calculation for a cylinder must be made by the formula:

S=[P(1.3D\2\+0.4d\2\)]/(D\2\-d\2\)

Where:

S=wall stress in pounds per square inch;
P=test pressure prescribed for water jacket test, i.e., at least two 
times service pressure, in pounds per square inch;
D=outside diameter in inches;
d=inside diameter in inches.

    (f) Heat treatment. The completed cylinders must be uniformly and 
properly heat-treated prior to tests.
    (g) Openings in container. Openings in cylinders must comply with 
the following:
    (1) Each opening in the container, except those for safety devices, 
must be provided with a fitting, boss, or pad, securely attached to the 
container by brazing or by welding or by threads. If threads are used, 
they must comply with the following:
    (i) Threads must be clean cut, even, without checks, and tapped to 
gauge.
    (ii) Taper threads must be of a length not less than that specified 
for American Standard taper pipe threads.
    (iii) Straight threads, having at least 4 engaged threads, must 
have a tight fit and calculated shear strength of at least 10 times the 
test pressure of the container. Gaskets, adequate to prevent leakage, 
are required.
    (2) Closure of a fitting, boss, or pad must be adequate to prevent 
leakage.
    (h) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test, as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. A pressure gauge must permit a 
reading to an accuracy of 1 percent. An expansion gauge must permit 
reading of total expansion to an accuracy of either 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the test pressure. If, due to failure of the test 
apparatus, the test pressure cannot be maintained, the test may be 
repeated at a pressure increased by 10 percent or 100 pounds per square 
inch, whichever is the lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of the 
total volumetric expansion at test pressure.
    (4) Containers must be tested as follows:
    (i) Each container to at least 2 times service pressure; or
    (ii) One container out of each lot of 200 or less to at least 3 
times service pressure. Others must be examined under pressure of 2 
times service pressure and show no defects.
    (i) Flattening test for spheres and cylinders. Spheres and 
cylinders must be subjected to a flattening test as follows:
    (1) One sphere taken at random out of each lot of 200 or less must 
be subjected to a flattening test as follows:
    (i) The test must be performed after the hydrostatic test.
    (ii) The test must be between parallel steel plates on a press with 
a welded seam at right angles to the plates. Any projecting 
appurtenances may be cut off (by mechanical means only) prior to 
crushing.
    (2) One cylinder taken at random out of each lot of 200 or less 
must be subjected to a flattening test, as follows:
    (i) The test must be performed after the hydrostatic test.
    (ii) The test must be between knife edges, wedge shaped, 60 deg. 
angle, rounded to \1/2\ inch radius. For lots of 30 or less, physical 
tests are authorized to be made on a ring at least 8 inches long cut 
from each cylinder and subjected to the same heat treatment as the 
finished cylinder.
    (j) Physical test and specimens for spheres and cylinders. Spheres 
and cylinders must be subjected to a physical test as follows:
    (1) Physical test for spheres are required on 2 specimens cut from 
a flat representative sample plate of the same heat taken at random 
from the steel used to produce the sphere. This flat steel from which 
the 2 specimens are to be cut must receive the same heat-treatment as 
the spheres themselves. Sample plates must be taken for each lot of 200 
or less spheres.
    (2) Specimens for spheres must have a gauge length 2 inches with a 
width not over 1\1/2\ inches, or a gauge length at least 24 times the 
thickness with a width not over 6 times the thickness is authorized 
when a wall is not over \3/16\ inch thick.
    (3) Physical test for cylinders is required on 2 specimens cut from 
1 cylinder taken at random out of each lot of 200 or less. For lots of 
30 or less, physical tests are authorized to be made on a ring at least 
8 inches long cut from each cylinder and subjected to the same heat 
treatment as the finished cylinder.
    (4) Specimens for cylinders must conform to the following:
    (i) A gauge length of 8 inches with a width not over 1\1/2\ inches, 
or a gauge length of 2 inches with a width not over 1\1/2\ inches, or a 
gauge length at least 24 times the thickness with a width not over 6 
times the thickness is authorized when a cylinder wall is not over \3/
16\ inch thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within 1 inch of each end of the reduced 
section. Heating of the specimen for any purpose is not authorized.
    (5) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch and the strain indicator reading being set at the 
calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination. 

[[Page 8353]]

    (k) Acceptable results for physical and flattening tests. Either of 
the following is an acceptable result:
    (1) An Elongation of at least 40 percent for a 2 inch gauge length 
or at least 20 percent in other cases and yield strength not over 73 
percent of tensile strength. In this instance, the flattening test is 
not required.
    (2) An elongation of at least 20 percent for a 2 inch gauge length 
or 10 percent in other cases. Flattening is required to 50 percent of 
the original outside diameter without cracking.
    (l) Rejected cylinders. Reheat-treatment is authorized for rejected 
cylinders. Subsequent thereto, containers must pass all prescribed 
tests to be acceptable. Repair of welded seams by welding prior to 
reheat-treatment is authorized.
    (m) Marking. Marking on each container by stamping plainly and 
permanently are only authorized where the metal is at least 0.09 inch 
thick, or on a metal nameplate permanently secured to the container by 
means other than soft solder, or by means that would not reduce the 
wall thickness.


Sec. 178.55  Specification 4B240ET welded or brazed cylinders.

    (a) Type, spinning process, size and service pressure. A DOT 
4B240ET cylinder is a brazed type cylinder made from electric 
resistance welded tubing. The maximum water capacity of this cylinder 
is 12 pounds or 333 cubic inches and the service must be 240 pounds per 
square inch. The maximum outside diameter of the shell must be five 
inches and maximum length of the shell is 21 inches. Cylinders closed 
in by a spinning process are authorized.
    (b) Steel. Open-hearth, basic oxygen, or electric steel of uniform 
quality must be used. Plain carbon steel content may not exceed the 
following: Carbon, 0.25; phosphorus, 0.045; sulfur, 0.050. The addition 
of other elements for alloying effect is prohibited.
    (c) Identification of material. Material must be identified by any 
suitable method.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is permitted that is likely 
to weaken the finished cylinder appreciably. A reasonably smooth and 
uniform surface finish is required. Heads may be attached to shells by 
lap brazing or may be formed integrally. The thickness of the bottom of 
cylinders welded or formed by spinning is, under no condition, to be 
less than two times the minimum wall thickness of the cylindrical 
shell. Such bottom thicknesses must be measured within an area bounded 
by a line representing the points of contact between the cylinder and 
the floor when the cylinder is in a vertical position. Seams must 
conform to the following:
    (1) Circumferential seams must be by brazing only. Heads must be 
attached to shells by the lap brazing method and must overlap not less 
than four times the wall thickness. Brazing material must have a 
melting point of not less than 1000 deg. F. Heads must have a driving 
fit with the shell unless the shell is crimped, swedged, or curled over 
the skirt or flange of the head and be thoroughly brazed until complete 
penetration of the joint by the brazing material is secured. Brazed 
joints may be repaired by brazing.
    (2) Longitudinal seams in shell must be by electric resistance 
welded joints only. No repairs to longitudinal joints is permitted.
    (3) Welding procedures and operators must be qualified in 
accordance with CGA Pamphlet C-3.
    (e) Welding or brazing. Only the attachment, by welding or brazing, 
to the tops and bottoms of cylinders of neckrings, footrings, handles, 
bosses, pads, and valve protection rings is authorized. Provided that 
such attachments and the portion of the container to which they are 
attached are made of weldable steel, the carbon content of which may 
not exceed 0.25 percent.
    (f) Wall thickness. The wall stress must be at least two times the 
service pressure and may not exceed 18,000 pounds per square inch. The 
minimum wall thickness is 0.044 inch. Calculation must be made by the 
following formula:

S=[P(1.3D2+0.4d2)]/(D2-d2)

where:

S=wall stress in pounds per square inch;
P=2 times service pressure;
D=outside diameter in inches;
d=inside diameter in inches.

    (g) Heat treatment. Heads formed by drawing or pressing must be 
uniformly and properly heat treated prior to tests. Cylinders with 
integral formed heads or bases must be subjected to a normalizing 
operation. Normalizing and brazing operations may be combined, provided 
the operation is carried out at a temperature in excess of the upper 
critical temperature of the steel.
    (h) Openings in cylinders. Openings in cylinders must comply with 
the following:
    (1) Each opening in cylinders, except those for safety devices, 
must be provided with a fitting, boss, or pad, securely attached to the 
cylinder by brazing or by welding or by threads. A fitting, boss, or 
pad must be of steel suitable for the method of attachment employed, 
and which need not be identified or verified as to analysis, except 
that if attachment is by welding, carbon content may not exceed 0.25 
percent. If threads are used, they must comply with the following:
    (i) Threads must be clean cut, even without checks, and tapped to 
gauge.
    (ii) Taper threads to be of length not less than as specified for 
American Standard taper pipe threads.
    (iii) Straight threads, having at least 4 engaged threads, to have 
tight fit and calculated shear strength at least 10 times the test 
pressure of the cylinder; gaskets required, adequate to prevent 
leakage.
    (2) Closure of a fitting, boss, or pad must be adequate to prevent 
leakage.
    (i) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy of either 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the test pressure. If, due to failure of the test 
apparatus, the test pressure cannot be maintained, the test may be 
repeated at a pressure increased by 10 percent or 100 pounds per square 
inch, whichever is the lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) Cylinders must be tested as follows:
    (i) At least one cylinder selected at random out of each lot of 200 
or less must be tested as outlined in paragraphs (i)(1), (i)(2), and 
(i)(3) of this section to at least two times service pressure.
    (ii) All cylinders not tested as outlined in paragraph (i)(4)(i) of 
this section must be examined under pressure of at least two times 
service pressure and show no defect.
    (5) Each 1000 cylinders or less successively produced each day must 
constitute a lot. One cylinder must be selected from each lot and 
hydrostatically tested to destruction. If this cylinder bursts below 
five times the service pressure, then two additional cylinders must be 
selected and subjected to this test. If either of these 

[[Page 8354]]
cylinders fails by bursting below five times the service pressure then 
the entire lot must be rejected. All cylinders constituting a lot must 
be of identical size, construction heat-treatment, finish, and quality.
    (j) Flattening test. Following the hydrostatic test, one cylinder 
taken at random out of each lot of 200 or less, must be subjected to a 
flattening test that is between knife edges, wedge shaped, 60 deg. 
angle, rounded to \1/2\ inch radius.
    (k) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material, as follows:
    (1) The test is required on 2 specimens cut from 1 cylinder, or 
part thereof heat-treated as required, taken at random out of each lot 
of 200 or less in the case of cylinders of capacity greater than 86 
cubic inches and out of each lot of 500 or less for cylinders having a 
capacity of 86 cubic inches or less.
    (2) Specimens must conform to the following:
    (i) A gauge length of 8 inches with a width not over 1\1/2\ inches, 
a gauge length of 2 inches with a width not over 1\1/2\ inches, or a 
gauge length at least 24 times the thickness with a width not over 6 
times the thickness is authorized when a cylinder wall is not over \3/
16\ inch thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within one inch of each end of the 
reduced section.
    (iii) When size of cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold by pressure only, not by blows. 
When specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch and the strain indicator reading being set at the 
calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed 1/8 
inch per minute during yield strength determination.
    (l) Acceptable results for physical and flattening tests. 
Acceptable results for the physical and flattening tests are an 
elongation of at least 40 percent for a 2 inch gauge length or at least 
20 percent in other cases and a yield strength not over 73 percent of 
tensile strength. In this instance the flattening test is required, 
without cracking, to six times the wall thickness with a weld 90 deg. 
from the direction of the applied load. Two rings cut from the ends of 
length of pipe used in production of a lot may be used for the 
flattening test provided the rings accompany the lot which they 
represent in all thermal processing operations. At least one of the 
rings must pass the flattening test.
    (m) Leakage test. All spun cylinders and plugged cylinders must be 
tested for leakage by gas or air pressure after the bottom has been 
cleaned and is free from all moisture, subject to the following 
conditions:
    (1) Pressure, approximately the same as but no less than service 
pressure, must be applied to one side of the finished bottom over an 
area of at least \1/16\ of the total area of the bottom but not less 
than \3/4\ inch in diameter, including the closure, for at least 1 
minute, during which time the other side of the bottom exposed to 
pressure must be covered with water and closely examined for 
indications of leakage. Except as provided in paragraph (n) of this 
section, cylinders which are leaking must be rejected.
    (2) A spun cylinder is one in which an end closure in the finished 
cylinder has been welded by the spinning process.
    (3) A plugged cylinder is one in which a permanent closure in the 
bottom of a finished cylinder has been effected by a plug.
    (4) As a safety precaution, if the manufacturer elects to make this 
test before the hydrostatic test, he should design his apparatus so 
that the pressure is applied to the smallest area practicable, around 
the point of closure, and so as to use the smallest possible volume of 
air or gas.
    (n) Rejected cylinders. Repairs of rejected cylinders is 
authorized. Cylinders that are leaking must be rejected, except that:
    (1) Spun cylinders rejected under the provisions of paragraph (m) 
of this section may be removed from the spun cylinder category by 
drilling to remove defective material, tapping, and plugging.
    (2) Brazed joints may be rebrazed.
    (3) Subsequent to the operations noted in paragraphs (n)(1) and 
(n)(2) of this section, acceptable cylinders must pass all prescribed 
tests.
    (o) Marking. Markings on each cylinder must be by stamping plainly 
and permanently on shoulder, top head, neck or valve protection collar 
which is permanently attached to the cylinders and forming an integral 
part thereof, provided that cylinders not less than 0.090 inch thick 
may be stamped on the side wall adjacent to top head.


Sec. 178.56  Specification 4AA480 welded steel cylinders.

    (a) Type, size, and service pressure. A DOT 4AA480 cylinder is a 
welded steel cylinder having a water capacity (nominal) not over 1,000 
pounds water capacity and a service pressure of 480 pounds per square 
inch. Closures welded by spinning process not permitted.
    (b) Steel. The limiting chemical composition of steel authorized by 
this specification must be as shown in Table I of Appendix A to this 
part.
    (c) Identification of material. Material must be identified by any 
suitable method except that plates and billets for hotdrawn cylinders 
must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is permitted that is likely 
to weaken the finished cylinder appreciably. A reasonably smooth and 
uniform surface finish is required. Exposed bottom welds on cylinders 
over 18 inches long must be protected by footrings. Minimum thickness 
of heads and bottoms may not be less than 90 percent of the required 
thickness of the side wall. Seams must be made as follows:
    (1) Circumferential seams must be welded. Brazing is not 
authorized.
    (2) Longitudinal seams are not permitted.
    (3) Welding procedures and operators must be qualified in 
accordance with CGA Pamphlet C-3. 

[[Page 8355]]

    (e) Welding. Only the welding of neckrings, footrings, bosses, 
pads, and valve protection rings to the tops and bottoms of cylinders 
is authorized. Provided that such attachments are made of weldable 
steel, the carbon content of which does not exceed 0.25 percent.
    (f) Wall thickness. The wall thickness of the cylinder must conform 
to the following:
    (1) For cylinders with an outside diameter over 5 inches, the 
minimum wall thickness is 0.078 inch. In any case, the minimum wall 
thickness must be such that the calculated wall stress at the minimum 
test pressure (in paragraph (i) of this section) may not exceed the 
lesser value of either of the following:
    (i) One-half of the minimum tensile strength of the material 
determined as required in paragraph (j) of this section; or
    (ii) 35,000 pounds per square inch.
    (2) Calculation must be made by the formula:

S=[P(1.3D2+0.4d2)]/(D2-d2)

Where:
S=wall stress in pounds per square inch;
P=minimum test pressure prescribed for water jacket test;
D=outside diameter in inches;
d=inside diameter in inches.

    (3) The ratio of tangential length to outside diameter may not 
exceed 4.0 for cylinders with a wall thickness less than 0.100 inch.
    (g) Heat treatment. Each cylinder must be uniformly and properly 
heat treated prior to tests. Any suitable heat treatment in excess of 
1100 deg. F is authorized except that liquid quenching is not 
permitted. Heat treatment must be accomplished after all forming and 
welding operations. Heat treatment is not required after welding 
weldable low carbon parts to attachments of similar material which have 
been previously welded to the top or bottom of cylinders and properly 
heat treated, provided such subsequent welding does not produce a 
temperature in excess of 400 deg. F., in any part of the top or bottom 
material.
    (h) Openings in cylinders. Openings in cylinders must conform to 
the following:
    (1) All openings must be in the heads or bases.
    (2) Each opening in the cylinder, except those for safety devices, 
must be provided with a fitting boss, or pad, securely attached to the 
cylinder by welding or by threads. If threads are used they must comply 
with the following:
    (i) Threads must be clean-cut, even without checks and cut to 
gauge.
    (ii) Taper threads to be of length not less than as specified for 
American Standard taper pipe threads.
    (iii) Straight threads having at least 6 engaged threads, must have 
a tight fit and a calculated shear strength at least 10 times the test 
pressure of the cylinder. Gaskets, adequate to prevent leakage, are 
required.
    (3) Closure of a fitting, boss or pad must be adequate to prevent 
leakage.
    (i) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test as follows:
    (1) The test must be by water jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy of either 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds or 
sufficiently longer to assure complete expansion. Any internal pressure 
applied after heat-treatment and before the official test may not 
exceed 90 percent of the test pressure. If, due to failure of test 
apparatus, the test pressure cannot be maintained, the test may be 
repeated at a pressure increased by 10 percent or 100 pounds per square 
inch, whichever is lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of the 
total volumetric expansion at test pressure.
    (4) Cylinders must be tested as follows:
    (i) At least one cylinder selected at random out of each lot of 200 
or less must be tested as described in paragraphs (i)(1), (i)(2), and 
(i)(3) of this section, to at least two times service pressure. If a 
selected cylinder fails, then two additional specimens must be selected 
at random from the same lot and subjected to the prescribed test. If 
either of these fails the test, then each cylinder in that lot must be 
so tested; and
    (ii) Each cylinder not tested as prescribed in paragraph (i)(4)(i) 
of this section must be examined under pressure of at least two times 
service pressure and must show no defect. A cylinder showing a defect 
must be rejected unless it may be requalified under paragraph (m) of 
this section.
    (j) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material, as follows:
    (1) The test is required on 2 specimens cut from one cylinder 
having passed the hydrostatic test, or part thereof heat-treated as 
required, taken at random out of each lot of 200 or less.
    (2) Specimens must conform to the following:
    (i) A gauge length of 8 inches with a width not over 1\1/2\ inches, 
a gauge length of 2 inches with a width not over 1\1/2\ inches, or a 
gauge length at least 24 times the thickness with a width not over 6 
times thickness is authorized when the cylinder wall is not over \3/16\ 
inch thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within one inch of each end of the 
reduced section.
    (iii) When size of cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold, by pressure only, not by blows. 
When specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load''), corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
reference must be set while the specimen is under a stress of 12,000 
pounds per square inch and the strain indicator reading being set at 
the calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (k) Elongation. Physical test specimens must show at least a 40 
percent elongation for 2-inch gauge lengths or at least a 20 percent 
elongation in other cases. Except that these elongation percentages may 
be reduced numerically by 2 for 2-inch 

[[Page 8356]]
specimens and by 1 in other cases for each 7,500 pounds per square inch 
increment of tensile strength above 50,000 pounds per square inch to a 
maximum of four such increments.
    (l) Tests of welds. Welds must be tested as follows:
    (1) Tensile test. A specimen must be cut from one cylinder of each 
lot of 200 or less, or a welded test plate. The welded test plate must 
be of one of the heats in the lot of 200 or less which it represents, 
in the same condition and approximately the same thickness as the 
cylinder wall except that it may not be of a lesser thickness than that 
required for a quarter size Charpy impact specimen. The weld must be 
made by the same procedures and subjected to the same heat treatment as 
the major weld on the cylinder. The specimens must be taken across the 
major seam and must be prepared and tested in accordance with and must 
meet the requirements of CGA Pamphlet C-3. Should this specimen fail to 
meet the requirements, specimens may be taken from two additional 
cylinders or welded test plates from the same lot and tested. If either 
of the latter specimens fail to meet the requirements, the entire lot 
represented must be rejected.
    (2) Guided bend test. A root bend test specimen must be cut from 
the cylinder or a welded test plate, used for the tensile test 
specified in paragraph (l)(1) of this section. Specimens must be taken 
from across the major seam and must be prepared and tested in 
accordance with and must meet the requirements of CGA Pamphlet C-3.
    (3) Alternate guided-bend test. This test may be used and must be 
as required by CGA Pamphlet C-3. The specimen must be bent until the 
elongation at the outer surface, adjacent to the root of the weld, 
between the lightly scribed gage lines-a to b, is at least 20 percent, 
except that this percentage may be reduced for steels having a tensile 
strength in excess of 50,000 pounds per square inch, as provided in 
paragraph (k) of this section.
    (m) Rejected cylinders. Reheat treatment of rejected cylinders is 
authorized. Subsequent thereto, cylinders must pass all prescribed 
tests to be acceptable. Repair of welded seams by welding is 
authorized.
    (n) Markings. Markings must be stamped plainly and permanently in 
one of the following locations on the cylinder:
    (1) On shoulders and top heads not less than 0.087 inch thick.
    (2) On neck, valve boss, valve protection sleeve, or similar part 
permanently attached to top end of cylinder.
    (3) On a plate attached to the top of the cylinder or permanent 
part thereof: sufficient space must be left on the plate to provide for 
stamping at least six retest dates: the plate must be at least \1/16\ 
inch thick and must be attached by welding or by brazing at a 
temperature of at least 1100 deg. F, throughout all edges of the plate.
    (4) Variations in location of markings authorized only when 
necessitated by lack of space.


Sec. 178.57  Specification 4L welded insulated cylinders.

    (a) Type, size, service pressure, and design service temperature. A 
DOT 4L cylinder is a fusion welded insulated cylinder with a water 
capacity (nominal) not over 1,000 pounds water capacity and a service 
pressure of at least 40 but not greater than 500 pounds per square inch 
conforming to the following requirements:
    (1) For liquefied hydrogen service, the cylinders must be designed 
to stand on end, with the axis of the cylindrical portion vertical.
    (2) The design service temperature is the coldest temperature for 
which a cylinder is suitable. The required design service temperatures 
for each cryogenic liquid is as follows:

------------------------------------------------------------------------
         Cryogenic liquid                Design service temperature     
------------------------------------------------------------------------
Argon............................  Minus 320 deg. F or colder.          
Helium...........................  Minus 452 deg. F or colder.          
Hydrogen.........................  Minus 423 deg. F or colder.          
Neon.............................  Minus 411 deg. F or colder.          
Nitrogen.........................  Minus 320 deg. F or colder.          
Oxygen...........................  Minus 320 deg. F or colder.          
------------------------------------------------------------------------

    (b) Material. Material use in the construction of this 
specification must conform to the following:
    (1) Inner containment vessel (cylinder). Designations and limiting 
chemical compositions of steel authorized by this specification must be 
as shown in Table 1 in paragraph (o) of this section.
    (2) Outer jacket. Steel or aluminum may be used subject to the 
requirements of paragraph (o)(2) of this section.
    (c) Identification of material. Material must be identified by any 
suitable method.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart and to the following requirements:
    (1) No defect is permitted that is likely to weaken the finished 
cylinder appreciably. A reasonably smooth and uniform surface finish is 
required. The shell portion must be a reasonably true cylinder.
    (2) The heads must be seamless, concave side to the pressure, 
hemispherical or ellipsoidal in shape with the major diameter not more 
than twice the minor diameter. Minimum thickness of heads may not be 
less than 90 percent of the required thickness of the sidewall. The 
heads must be reasonably true to shape, have no abrupt shape changes, 
and the skirts must be reasonably true to round.
    (3) The surface of the cylinder must be insulated. The insulating 
material must be fire resistant. The insulation on non-evacuated 
jackets must be covered with a steel jacket not less than 0.060-inch 
thick or an aluminum jacket not less than 0.070 inch thick, so 
constructed that moisture cannot come in contact with the insulating 
material. If a vacuum is maintained in the insulation space, the 
evacuated jacket must be designed for a minimum collapsing pressure of 
30 psi differential whether made of steel or aluminum. The construction 
must be such that the total heat transfer, from the atmosphere at 
ambient temperature to the contents of the cylinder, will not exceed 
0.0005 Btu per hour, per Fahrenheit degree differential in temperature, 
per pound of water capacity of the cylinder. For hydrogen, cryogenic 
liquid service, the total heat transfer, with a temperature 
differential of 520 Fahrenheit degrees, may not exceed that required to 
vent 30 SCF of hydrogen gas per hour.
    (4) For a cylinder having a design service temperature colder than 
minus 320 deg. F, a calculation of the maximum weight of contents must 
be made and that weight must be marked on the cylinder as prescribed in 
Sec. 178.35.
    (5) Welding procedures and operators must be qualified in 
accordance with CGA Pamphlet C-3. In addition, an impact test of the 
weld must be performed in accordance with paragraph (l) of this section 
as part of the qualification of each welding procedure and operator.
    (e) Welding. Welding of the cylinder must be as follows:
    (1) All seams of the cylinder must be fusion welded. A means must 
be provided for accomplishing complete penetration of the joint. Only 
butt or joggle butt joints for the cylinder seams are authorized. All 
joints in the cylinder must have reasonably true alignment.
    (2) All attachments to the sidewalls and heads of the cylinder must 
be by fusion welding and must be of a weldable material complying with 
the impact requirements of paragraph (l) of this section. 

[[Page 8357]]

    (3) For welding the cylinder, each procedure and operator must be 
qualified in accordance with the sections of CGA Pamphlet C-3 that 
apply. In addition, impact tests of the weld must be performed in 
accordance with paragraph (l) of this section as part of the 
qualification of each welding procedure and operator.
    (4) Brazing, soldering and threading are permitted only for joints 
not made directly to the cylinder body. Threads must comply with the 
requirements of paragraph (h) of this section.
    (f) Wall thickness. The minimum wall thickness of the cylinder must 
be such that the calculated wall stress at the minimum required test 
pressure may not exceed the least value of the following:
    (1) 45,000 pounds per square inch.
    (2) One-half of the minimum tensile strength across the welded seam 
determined in paragraph (l) of this section.
    (3) One-half of the minimum tensile strength of the base metal 
determined as required in paragraph (j) of this section.
    (4) The yield strength of the base metal determined as required in 
paragraph (l) of this section.
    (5) Further provided that wall stress for cylinders having 
longitudinal seams may not exceed 85 percent of the value in paragraph 
(f)(4) of this section, whichever applies.
    (6) Calculation must be made by the following formula:

S=[P(1.3D\2\+0.4d\2\)]/(D\2\-d\2\)

where:

S=Wall stress in pounds per square inch;
P=Minimum test pressure prescribed for pressure test in pounds per 
square inch;
D=Outside diameter in inches;
d=Inside diameter in inches.

    (g) Heat treatment. Heat treatment is not permitted.
    (h) Openings in cylinder. Openings in cylinders must conform to the 
following:
    (1) Openings are permitted in heads only. They must be circular and 
may not exceed 3 inches in diameter or one third of the cylinder 
diameter, whichever is less. Each opening in the cylinder must be 
provided with a fitting, boss or pad, either integral with, or securely 
attached to, the cylinder body by fusion welding. Attachments to a 
fitting, boss or pad may be made by welding, brazing, mechanical 
attachment, or threading.
    (2) Threads must comply with the following:
    (i) Threads must be clean-cut, even, without checks and cut to 
gauge.
    (ii) Taper threads to be of a length not less than that specified 
for NPT.
    (iii) Straight threads must have at least 4 engaged threads, tight 
fit and calculated shear strength at least 10 times the test pressure 
of the cylinder. Gaskets, which prevent leakage and are inert to the 
hazardous material, are required.
    (i) Pressure test. Each cylinder, before insulating and jacketing, 
must be examined under a pressure of at least 2 times the service 
pressure maintained for at least 30 seconds without evidence of 
leakage, visible distortion or other defect. The pressure gauge must 
permit reading to an accuracy of 1 percent.
    (j) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, and elongation as follows:
    (1) The test is required on 2 specimens selected from material of 
each heat and in the same condition as that in the completed cylinder.
    (2) Specimens must conform to the following:
    (i) A gauge length of 8 inches with a width not over 1\1/2\ inches, 
a gauge length of 2 inches with width not over 1\1/2\ inches, or a 
gauge length at least 24 times thickness with a width not over 6 times 
thickness (authorized when cylinder wall is not over \3/16\ inch 
thick).
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within one inch of each end of the 
reduced section.
    (iii) When size of the cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold by pressure only, not by blows. 
When specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load''), corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic expansion of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on the elastic modulus of 
the material used. In the event of controversy, the entire stress-
strain diagram must be plotted and the yield strength determined from 
the 0.2 percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
reference must be set while the specimen is under a stress of 12,000 
pounds per square inch and the strain indicator reading being set at 
the calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (k) Acceptable results for physical tests. Physical properties must 
meet the limits specified in paragraph (o)(1), Table 1, for the 
particular steel in the annealed condition. The specimens must show at 
least a 20 percent elongation for a 2-inch gage length. Except that the 
percentage may be reduced numerically by 2 for each 7,500 pounds per 
square inch increment of tensile strength above 100,000 pounds per 
square inch to a maximum of 5 such increments. Yield strength and 
tensile strength must meet the requirements of paragraph (o)(1), Table 
1, of this section.
    (l) Tests of welds. Welds must be tested as follows:
    (1) Tensile test. A specimen must be cut from one cylinder of each 
lot of 200 or less, or welded test plate. The welded test plate must be 
of one of the heats in the lot of 200 or less which it represents, in 
the same condition and approximately the same thickness as the cylinder 
wall except that it may not of a lesser thickness than that required 
for a quarter size Charpy impact specimen. The weld must be made by the 
same procedures and subjected to the same heat treatment as the major 
weld on the cylinder. The specimen must be taken across the major seam 
and must be prepared and tested in accordance with and must meet the 
requirements of CGA Pamphlet C-3. Should this specimen fail to meet the 
requirements, specimens may be taken from two additional cylinders or 
welded test plates from the same lot and tested. If either of the 
latter specimens fails to meet the requirements, the entire lot 
represented must be rejected.
    (2) Guided bend test. A ``root'' bend test specimen must be cut 
from the cylinder or welded test plate, used for the tensile test 
specified in paragraph (l)(1) of this section and from any other seam 
or equivalent welded test plate if the seam is welded by a procedure 
different from that used for the major seam. Specimens must be taken 
across the particular seam being tested and 

[[Page 8358]]
must be prepared and tested in accordance with and must meet the 
requirements of CGA Pamphlet C-3.
    (3) Alternate guided-bend test. This test may be used and must be 
as specified in CGA Pamphlet C-3. The specimen must be bent until the 
elongation at the outer surface, adjacent to the root of the weld, 
between the lightly scribed gage lines-a to b, is at least 20 percent, 
except that this percentage may be reduced for steels having a tensile 
strength in excess of 100,000 pounds per square inch, as provided in 
paragraph (c) of this section.
    (4) Impact tests. One set of three impact test specimens (for each 
test) must be prepared and tested for determining the impact properties 
of the deposited weld metal--
    (i) As part of the qualification of the welding procedure.
    (ii) As part of the qualification of the operators.
    (iii) For each ``heat'' of welding rodor wire used.
    (iv) For each 1,000 feet of weld made with the same heat of welding 
rod or wire.
    (v) All impact test specimens must be of the Charpy type, keyhole 
or milled U-notch, and must conform in all respects to Figure 3 of ASTM 
E-23-60T. Each set of impact specimens must be taken across the weld 
and have the notch located in the weld metal. When the cylinder 
material thickness is 2.5 mm or thicker, impact specimens must be cut 
from a cylinder or welded test plate used for the tensile or bend test 
specimens. The dimension along the axis of the notch must be reduced to 
the largest possible of 10 mm, 7.5 mm, 5 mm or 2.5 mm, depending upon 
cylinder thickness. When the material in the cylinder or welded test 
plate is not of sufficient thickness to prepare 2.5 mm impact test 
specimens, 2.5 mm specimens must be prepared from a welded test plate 
made from \1/8\ inch thick material meeting the requirements specified 
in paragraph (o)(1), Table 1, of this section and having a carbon 
analysis of .05 minimum, but not necessarily from one of the heats used 
in the lot of cylinders. The test piece must be welded by the same 
welding procedure as used on the particular cylinder seam being 
qualified and must be subjected to the same heat treatment.
    (vi) Impact test specimens must be cooled to the design service 
temperature. The apparatus for testing the specimens must conform to 
the requirements of ASTM Standard E-23-60T. The test piece, as well as 
the handling tongs, must be cooled for a length of time sufficient to 
reach the service temperature. The temperature of the cooling device 
must be maintained within a range of plus or minus 3 deg. F. The 
specimen must be quickly transferred from the cooling device to the 
anvil of the testing machine and broken within a time lapse of not more 
than six seconds.
    (vii) The impact properties of each set of impact specimens may not 
be less than the values in the following table:

------------------------------------------------------------------------
                                                    Minimum             
                                                    impact      Minimum 
                                                     value      impact  
                                                   required      value  
                                                   for avg.    permitted
                Size of specimen                    of each     on one  
                                                    set of     only of a
                                                     three      set of  
                                                   specimens     three  
                                                   (ft.-lb.)  (ft.- lb.)
------------------------------------------------------------------------
10 mm x 10 mm...................................        15          10  
10 mm x 7.5 mm..................................        12.5         8.5
10 mm x 5 mm....................................        10           7.0
10 mm x 2.5 mm..................................         5           3.5
------------------------------------------------------------------------

    (viii) When the average value of the three specimens equals or 
exceeds the minimum value permitted for a single specimen and the value 
for more than one specimen is below the required average value, or when 
the value for one specimen is below the minimum value permitted for a 
single specimen, a retest of three additional specimens must be made. 
The value of each of these retest specimens must equal or exceed the 
required average value. When an erratic result is caused by a defective 
specimen, or there is uncertainty in test procedure, a retest is 
authorized.
    (m) Radiographic examination. Cylinders must be subject to a 
radiographic examination as follows:
    (1) The techniques and acceptability of radiographic inspection 
must conform to the standards set forth in CGA Pamphlet C-3.
    (2) One finished longitudinal seam must be selected at random from 
each lot of 100 or less successively produced and be radiographed 
throughout its entire length. Should the radiographic examination fail 
to meet the requirements of paragraph (m)(1) of this section, two 
additional seams of the same lot must be examined, and if either of 
these fail to meet the requirements of (m)(1) of this section, only 
those passing are acceptable.
    (n) Rejected cylinders. Reheat treatment of rejected cylinders is 
authorized. Subsequent thereto, cylinders must pass all prescribed 
tests to be acceptable. Welds may be repaired by suitable methods of 
fusion welding.
    (o) Authorized materials of construction. Authorized materials of 
construction are as follows:
    (1) Inner containment vessel (cylinder). Electric furnace steel of 
uniform quality must be used. Chemical analysis must conform to ASTM 
A240, Type 304 Stainless Steel. A heat of steel made under Table 1 and 
Table 2 of this paragraph (o)(1) is acceptable, even though its check 
chemical analysis is slightly out of the specified range, if it is 
satisfactory in all other respects, provided the tolerances shown in 
Table 3 of this paragraph (o)(1) are not exceeded. The following 
chemical analyses and physical properties are authorized:

                     Table 1.--Authorized Materials                     
------------------------------------------------------------------------
                                                    Chemical analysis,  
                  Designation                       limits in percent   
------------------------------------------------------------------------
Carbon1........................................  0.08 max.              
Manganese......................................  2.00 max.              
Phosphorus.....................................  0.045 max.             
Sulphur........................................  0.030 max.             
Silicon........................................  1.00 max.              
Nickel.........................................  8.00-10.50             
Chromium.......................................  18.00-20.00            
Molybdenum.....................................  None.                  
Titanium.......................................  None.                  
Columbium......................................  None.                  
------------------------------------------------------------------------
1 The carbon analysis must be reported to the nearest hundredth of one  
  percent.                                                              


[[Page 8359]]


                      Table 2.--Physical Properties                     
------------------------------------------------------------------------
                                                               Physical 
                                                              properties
                                                              (annealed)
------------------------------------------------------------------------
Tensile strength, p.s.i. (minimum).........................       75,000
Yield strength, p.s.i. (minimum)...........................       30,000
Elongation in 2 inches (minimum) percent...................         30.0
Elongation other permissible gauge lengths (minimum)                    
 percent...................................................         15.0
------------------------------------------------------------------------


                                       Table 3.--Check Analysis Tolerances                                      
----------------------------------------------------------------------------------------------------------------
                                                                                                      Tolerance 
                                                                                                      over the  
                                                                                                       maximum  
               Elements                             Limit or specified range (percent)                limit or  
                                                                                                      under the 
                                                                                                       minimum  
                                                                                                        limit   
----------------------------------------------------------------------------------------------------------------
Carbon...............................  To 0.030, incl.............................................         0.005
                                       Over 0.30 to 0.20, incl....................................         0.01 
Manganese............................  To 1.00 incl...............................................          .03 
                                       Over 1.00 to 3.00, incl....................................         0.04 
Phosphorus \1\.......................  To 0.040, incl.............................................         0.005
                                       Over 0.040 to 0.020 incl...................................         0.010
Sulphur..............................  To .40 incl................................................         0.005
Silicon..............................  To 1.00, incl..............................................         0.05 
Nickel...............................  Over 5.00 to 10.00, incl...................................         0.10 
                                       Over 10.00 to 20.00, incl..................................         0.15 
Chromium.............................  Over 15.00 to 20.00, incl..................................         0.20 
----------------------------------------------------------------------------------------------------------------
1 Rephosphorized steels not subject to check analysis for phosphorus.                                           

    (2) Outer jacket. (i) Nonflammable cryogenic liquids. Cylinders 
intended for use in the transportation of nonflammable cryogenic liquid 
must have an outer jacket made of steel or aluminum.
    (ii) Flammable cryogenic liquids. Cylinders intended for use in the 
transportation of flammable cryogenic liquid must have an outer jacket 
made of steel.
    (p) Markings. (1) Markings must be stamped plainly and permanently 
on shoulder or top head of jacket or on a permanently attached plate or 
head protective ring.
    (2) The letters ``ST'', followed by the design service temperature 
(for example, ST-423F), must be marked on cylinders having a design 
service temperature of colder than minus 320 deg. F only. Location to 
be just below the DOT mark.
    (3) The maximum weight of contents, in pounds (for example, ``Max. 
Content 51 #''), must be marked on cylinders having a design service 
temperature colder than minus 320 deg. F only. Location to be near 
symbol.
    (4) Special orientation instructions must be marked on the cylinder 
(for example, THIS END UP), if the cylinder is used in an orientation 
other than vertical with openings at the top of the cylinder.
    (5) If the jacket of the cylinder is constructed of aluminum, the 
letters ``AL'' must be marked after the service pressure marking. 
Example: DOT-4L150 AL.
    (6) Except for serial number and jacket material designation, each 
marking prescribed in this paragraph (p) must be duplicated on each 
cylinder by any suitable means.
    (q) Inspector's report. In addition to the information required by 
Sec. 178.35, the inspector's reports must contain information on:
    (1) The jacket material and insulation type;
    (2) The design service temperature ( deg. F); and
    (3) The impact test results, on a lot basis.


Sec. 178.58  Specification 4DA welded steel cylinders for aircraft use.

    (a) Type, size, and service pressure. A DOT 4DA is a welded steel 
sphere (two seamless hemispheres) or a circumferentially welded 
cylinder (two seamless drawn shells) with a water capacity not over 100 
pounds and a service pressure of at least 500 but not over 900 pounds 
per square inch.
    (b) Steel. Open-hearth or electric steel of uniform quality must be 
used. A heat of steel made under Table 1 of this paragraph (b), check 
chemical analysis of which is slightly out of the specified range, is 
acceptable, if satisfactory in all other respects, provided the 
tolerances shown in Table 2 of this paragraph (b) are not exceeded 
except as approved by the Associate Administrator. The following 
chemical analyses are authorized:

                     Table 1.--Authorized Materials                     
------------------------------------------------------------------------
                      4130                               Percent        
------------------------------------------------------------------------
Carbon.........................................  0.28/0.33.             
Manganese......................................  0.40/0.60.             
Phosphorus.....................................  0.040 max.             
Sulfur.........................................  0.040 max.             
Silicon........................................  0.15/0.35.             
Chromium.......................................  0.80/1.10.             
Molybdenum.....................................  0.15/0.25.             
------------------------------------------------------------------------


[[Page 8360]]


                                       Table 2.--Check Analysis Tolerances                                      
----------------------------------------------------------------------------------------------------------------
                                                                                        Tolerance (percent) over
                                                                                          the maximum limit or  
                                                                                         under the minimum limit
               Element                      Limit or maximum specified  (percent)      -------------------------
                                                                                           Under         Over   
                                                                                          minimum      maximum  
                                                                                           limit        limit   
----------------------------------------------------------------------------------------------------------------
Carbon..............................  Over 0.15 to 0.40 incl..........................          .03          .04
Manganese...........................  To 0.60 incl....................................          .03          .03
Phosphorus \1\......................  All ranges......................................  ...........          .01
Sulphur.............................  All ranges......................................  ...........          .01
Silicon.............................  To 0.30 incl....................................          .02          .03
                                      Over 0.30 to 1.00 incl..........................          .05          .05
Chromium............................  To 0.90 incl....................................          .03          .03
                                      Over 0.90 to 2.10 incl..........................          .05          .05
Molybdenum..........................  To 0.20 incl....................................          .01          .01
                                      Over 0.20 to 0.40, incl.........................          .02          .02
----------------------------------------------------------------------------------------------------------------
\1\ Rephosphorized steels not subject to check analysis for phosphorus.                                         

    (c) Identification of material. Materials must be identified by any 
suitable method except that plates and billets for hot-drawn containers 
must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured in accordance with 
the following requirements:
    (1) By best appliances and methods. No defect is acceptable that is 
likely to weaken the finished container appreciably. A reasonably 
smooth and uniform surface finish is required. No abrupt change in wall 
thickness is permitted. Welding procedures and operators must be 
qualified in accordance with CGA Pamphlet C-3.
    (2) All seams of the sphere or cylinders must be fusion welded. 
Seams must be of the butt or joggle butt type and means must be 
provided for accomplishing complete penetration of the joint.
    (e) Welding. Attachments to the container are authorized by fusion 
welding provided that such attachments are made of weldable steel, the 
carbon content of which may not exceed 0.25 percent except in the case 
of 4130 steel.
    (f) Wall thickness. The minimum wall thickness must be such that 
the wall stress at the minimum specified test pressure may not exceed 
67 percent of the minimum tensile strength of the steel as determined 
from the physical and burst tests required and may not be over 70,000 
p.s.i. For any diameter container, the minimum wall thickness is 0.040 
inch. Calculations must be made by the formulas in paragraph (f)(1) or 
(f)(2) of this section:
    (1) Calculation for a sphere must be made by the following formula:

S=PD/4tE

where:

S=Wall stress in pounds per square inch;
P=Test pressure prescribed for water jacket test, i.e., at least 2 
times service pressure, in pounds per square inch;
D=Outside diameter in inches;
t=Minimum wall thickness in inches;
E=0.85 (provides 85 percent weld efficiency factor which must be 
applied in the girth weld area and heat affected zones which zone must 
extend a distance of 6 times wall thickness from center line of weld);
E=1.0 (for all other areas).

    (2) Calculation for a cylinder must be made by the following 
formula:

S=[P(1.3D2+0.4d2)]/(D2-d2)

Where:

S=wall stress in pounds per square inch;
P=test pressure prescribed for water jacket test, i.e., at least 2 
times service pressure, in pounds per square inch;
D=outside diameter in inches;
d=inside diameter in inches.

    (g) Heat treatment. The completed containers must be uniformly and 
properly heat-treated prior to tests. Heat-treatment of containers of 
the authorized analysis must be as follows:
    (1) All containers must be quenched by oil, or other suitable 
medium except as provided in paragraph (l)(iv) of this section.
    (2) The steel temperature on quenching must be that recommended for 
the steel analysis, but may not exceed 1,750 deg. F.
    (3) The steel must be tempered at the temperature most suitable for 
the analysis except that in no case shall the tempering temperature be 
less than 1,000 deg. F.
    (4) The steel may be normalized at a temperature of 1,650 deg. F 
instead of being quenched, and containers so normalized need not be 
tempered.
    (5) All cylinders, if water quenched or quenched with a liquid 
producing a cooling rate in excess of 80 percent of the cooling rate of 
water, must be inspected by the magnetic particle or dye penetrant 
method to detect the presence of quenching cracks. Any cylinder found 
to have a quench crack must be rejected and may not be requalified.
    (h) Openings in container. Openings in the container must comply 
with the following requirements:
    (1) Each opening in the container must be provided with a fitting, 
boss, or pad of weldable steel securely attached to the container by 
fusion welding.
    (2) Attachments to a fitting, boss, or pad must be adequate to 
prevent leakage. Threads must comply with the following:
    (i) Threads must be clean cut, even, without checks, and tapped to 
gauge.
    (ii) Taper threads to be of length not less than as specified for 
American Standard taper pipe threads.
    (iii) Straight threads, having at least 4 engaged threads, to have 
tight fit and calculated shear strength at least 10 times the test 
pressure of the container; gaskets required, adequate to prevent 
leakage.
    (i) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to accuracy either of 1 percent or 0.1 cubic 
centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the 

[[Page 8361]]
test pressure. If, due to failure of the test apparatus, the test 
pressure cannot be maintained, the test may be repeated at a pressure 
increased by 10 percent or 100 pounds per square inch, whichever is the 
lower.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) Each container must be tested to at least 2 times service 
pressure.
    (j) Burst test. One container taken at random out of 200 or less 
must be hydrostatically tested to destruction. The rupture pressure 
must be included as part of the inspector's report.
    (k) Flattening test. Spheres and cylinders must be subjected to a 
flattening test as follows:
    (1) Flattening test for spheres. One sphere taken at random out of 
each lot of 200 or less must be subjected to a flattening test as 
follows:
    (i) The test must be performed after the hydrostatic test.
    (ii) The test must be at the weld between the parallel steel plates 
on a press with a welded seam, at right angles to the plates. Any 
projecting appurtenances may be cut off (by mechanical means only) 
prior to crushing.
    (2) Flattening test for cylinders. One cylinder taken at random out 
of each lot of 200 or less, must be subjected to a flattening test as 
follows:
    (i) The test must be performed after the hydrostatic test.
    (ii) The test must between knife edges, wedge shaped, 60 deg. 
angle, rounded to \1/2\ inch radius; test
    (l) Radiographic inspection. Radiographic examination is required 
on all welded joints which are subjected to internal pressure, except 
that at the discretion of the disinterested inspector, openings less 
than 25 percent of the sphere diameter need not be subjected to 
radiographic inspection. Evidence of any defects likely to seriously 
weaken the container must be cause for rejection.
    (m) Physical test and specimens for spheres and cylinders. Spheres 
and cylinders must be subjected to a physical test as follows:
    (1) A physical test for a sphere is required on 2 specimens cut 
from a flat representative sample plate of the same heat taken at 
random from the steel used to produce the sphere. This flat steel from 
which the 2 specimens are to be cut must receive the same heat-
treatment as the spheres themselves. Sample plates to be taken for each 
lot of 200 or less spheres.
    (2) Specimens for spheres have a gauge length 2 inches with a width 
not over 1\1/2\ inches, or a gauge length at least 24 times thickness 
with a width not over 6 times thickness is authorized when wall of 
sphere is not over \3/16\ inch thick.
    (3) A physical test for cylinders is required on 2 specimens cut 
from 1 cylinder taken at random out of each lot of 200 or less.
    (4) Specimens for cylinder must conform to the following:
    (i) A gauge length of 8 inches with a width not over 1\1/2\ inches, 
a gauge length of 2 inches with a width not over 1\1/2\ inches, a gauge 
length at least 24 times thickness with a width not over 6 times 
thickness is authorized when a cylinder wall is not over \3/16\ inch 
thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within 1 inch of each end of the reduced 
section.
    (iii) Heating of a specimen for any purpose is not authorized.
    (5) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch and the strain indicator reading being set at the 
calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (n) Acceptable results for physical, flattening, and burst tests. 
The following are acceptable results of the physical, flattening and 
burst test:
    (1) Elongation must be at least 20 percent for a 2-inch gauge 
length or 10 percent in other cases.
    (2) Flattening is required to 50 percent of the original outside 
diameter without cracking.
    (3) Burst pressure must be at least 3 times service pressure.
    (o) Rejected containers. Reheat-treatment of rejected cylinders is 
authorized. Subsequent thereto, containers must pass all prescribed 
tests to be acceptable. Repair of welded seams by welding prior to 
reheat-treatment is authorized.
    (p) Marking. Markings on each container must be stamped plainly and 
permanently on a permanent attachment or on a metal nameplate 
permanently secured to the container by means other than soft solder.


Sec. 178.59  Specification 8 steel cylinders with porous fillings for 
acetylene.

    (a) Type and service pressure. A DOT 8 cylinder is a seamless 
cylinder with a service pressure of 250 pounds per square inch. The 
following steel is authorized:
    (1) A longitudinal seam if forge lap welded;
    (2) Attachment of heads by welding or by brazing by dipping 
process; or
    (3) A welded circumferential body seam if the cylinder has no 
longitudinal seam.
    (b) Steel. Open-hearth, electric or basic oxygen process steel of 
uniform quality must be used. Content percent may not exceed the 
following: Carbon, 0.25; phosphorus, 0.045; sulphur, 0.050.
    (c) Identification of steel. Materials must be identified by any 
suitable method except that plates and billets for hot-drawn cylinders 
must be marked with the heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is acceptable that is 
likely to weaken the finished cylinder appreciably. A reasonably smooth 
and uniform surface finish is required. Welding procedures and 
operators must be qualified in accordance with CGA Pamphlet C-3.
    (e) Exposed bottom welds. Exposed bottom welds on cylinders over 18 
inches long must be protected by footrings.
    (f) Heat treatment. Body and heads formed by drawing or pressing 
must be uniformly and properly heat treated prior to tests.
    (g) Openings. Openings in the cylinders must comply with the 
following:
    (1) Standard taper pipe threads are required;
    (2) Length may not be less than as specified for American Standard 
pipe threads; tapped to gauge; clean cut, even, and without checks. 

[[Page 8362]]

    (h) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy of either 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the test pressure.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) One cylinder out of each lot of 200 or less must be 
hydrostatically tested to at least 750 pounds per square inch. 
Cylinders not so tested must be examined under pressure of between 500 
and 600 pounds per square inch and show no defect. If hydrostatically 
tested cylinder fails, each cylinder in the lot may be hydrostatically 
tested and those passing are acceptable.
    (i) Leakage test. Cylinders with bottoms closed in by spinning must 
be subjected to a leakage test by setting the interior air or gas 
pressure to not less than the service pressure. Cylinders which leak 
must be rejected.
    (j) Physical test. A physical test must be conducted as follows:
    (1) The test is required on 2 specimens cut longitudinally from 1 
cylinder or part thereof taken at random out of each lot of 200 or 
less, after heat treatment.
    (2) Specimens must conform to a gauge length of 8 inches with a 
width not over 1\1/2\ inches, a gauge length of 2 inches with width not 
over 1\1/2\, or a gauge length at least 24 times thickness with a width 
not over 6 times thickness is authorized when a cylinder wall is not 
over \3/16\ inch thick.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2 
offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch and the strain indicator reading being set at the 
calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per-minute during yield strength determination.
    (4) Yield strength may not exceed 73 percent of tensile strength. 
Elongation must be at least 40 percent in 2 inch or 20 percent in other 
cases.
    (k) Rejected cylinders. Reheat treatment of rejected cylinder is 
authorized. Subsequent thereto, cylinders must pass all prescribed 
tests to be acceptable. Repair by welding is authorized.
    (l) Porous filling. (1) Cylinders must be filled with a porous 
material in accordance with the following:
    (i) The porous material may not disintegrate or sag when wet with 
solvent or when subjected to normal service;
    (ii) The porous filling material must be uniform in quality and 
free of voids, except that a well drilled into the filling material 
beneath the valve is authorized if the well is filled with a material 
of such type that the functions of the filling material are not 
impaired;
    (iii) Overall shrinkage of the filling material is authorized if 
the total clearance between the cylinder shell and filling material, 
after solvent has been added, does not exceed \1/2\ of 1 percent of the 
respective diameter or length, but not to exceed \1/8\ inch, measured 
diametrically and longitudinally;
    (iv) The clearance may not impair the functions of the filling 
material;
    (v) The installed filling material must meet the requirements of 
CGA Pamphlet C-12; and
    (vi) Porosity of filling material may not exceed 80 percent except 
that filling material with a porosity of up to 92 percent may be used 
when tested with satisfactory results in accordance with CGA Pamphlet 
C-12.
    (2) When the porosity of each cylinder is not known, a cylinder 
taken at random from a lot of 200 or less must be tested for porosity. 
If the test cylinder fails, each cylinder in the lot may be tested 
individually and those cylinders that pass the test are acceptable.
    (3) For filling that is molded and dried before insertion in 
cylinders, porosity test may be made on a sample block taken at random 
from material to be used.
    (4) The porosity of the filling material must be determined. The 
amount of solvent at 70 deg. F for a cylinder:
    (i) Having shell volumetric capacity above 20 pounds water capacity 
(nominal) may not exceed the following:

------------------------------------------------------------------------
                                                               Maximum  
                                                               acetone  
                                                               solvent  
                 Percent porosity of filler                    percent  
                                                                shell   
                                                             capacity by
                                                                volume  
------------------------------------------------------------------------
90 to 92...................................................         43.4
87 to 90...................................................         42.0
83 to 87...................................................         40.0
80 to 83...................................................         38.6
75 to 80...................................................         36.2
70 to 75...................................................         33.8
65 to 70...................................................         31.4
------------------------------------------------------------------------

    (ii) Having volumetric capacity of 20 pounds or less water capacity 
(nominal), may not exceed the following:

------------------------------------------------------------------------
                                                               Maximum  
                                                               acetone  
                                                               solvent  
                 Percent porosity of filler                    percent  
                                                                shell   
                                                             capacity by
                                                                volume  
------------------------------------------------------------------------
90 to 92...................................................         41.8
83 to 90...................................................         38.5
80 to 83...................................................         37.1
75 to 80...................................................         34.8
70 to 75...................................................         32.5
65 to 70...................................................         30.2
------------------------------------------------------------------------

    (m) Tare weight. The tare weight is the combined weight of the 
cylinder proper, porous filling, valve, and solvent, without removable 
cap.
    (n) Duties of inspector. In addition to the requirements of 
Sec. 178.35, the inspector is required to--
    (1) Certify chemical analyses of steel used, signed by manufacturer 
thereof; also verify by, check analyses of samples taken from each heat 
or from 1 out of each lot of 200 or less, plates, shells, or tubes 
used.
    (2) Verify compliance of cylinder shells with all shell 
requirements; inspect inside before closing in both ends; verify heat 
treatment as proper; obtain all samples for all tests and for check 
analyses; witness all tests; verify threads by gauge; report volumetric 
capacity and minimum thickness of wall noted.
    (3) Prepare report on manufacture of steel shells in form 
prescribed in Sec. 178.35. Furnish one copy to manufacturer and three 
copies to the company that is to complete the cylinders. 

[[Page 8363]]

    (4) Determine porosity of filling and tare weights; verify 
compliance of marking with prescribed requirements; obtain necessary 
copies of steel shell reports; and furnish complete reports required by 
this specification to the person who has completed the manufacture of 
the cylinders and, upon request, to the purchaser. The test reports 
must be retained by the inspector for fifteen years from the original 
test date of the cylinder.
    (o) Marking. (1) Marking on each cylinder must be stamped plainly 
and permanently on or near the shoulder, top head, neck or valve 
protection collar which is permanently attached to the cylinder and 
forming integral part thereof.
    (2) Tare weight of cylinder, in pounds and ounces, must be marked 
on the cylinder.
    (3) Cylinders, not completed, when delivered must each be marked 
for identification of each lot of 200 or less.


Sec. 178.60  Specification 8AL steel cylinders with porous fillings for 
acetylene.

    (a) Type and service pressure. A DOT 8AL cylinder is a seamless 
steel cylinder with a service pressure of 250 pounds per square inch. 
However, the attachment of heads by welding or by brazing by dipping 
process and a welded circumferential body seam is authorized. 
Longitudinal seams are not authorized.
    (b) Authorized steel. The authorized steel is as specified in Table 
I of Appendix A to this part.
    (c) Identification of steel. Material must be identified by any 
suitable method except that plates and billets for hot-drawn cylinders 
must be marked with heat number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is permitted that is likely 
to weaken the finished cylinder appreciably. A reasonably smooth and 
uniform surface finish is required. Welding procedures and operators 
must be qualified in accordance with CGA Pamphlet C-3.
    (e) Footrings. Exposed bottom welds on cylinders over 18 inches 
long must be protected by footrings.
    (f) Welding or brazing. Welding or brazing for any purpose 
whatsoever is prohibited except as follows:
    (1) The attachment to the tops or bottoms of cylinders of 
neckrings, footrings, handlers, bosses, pads, and valve protecting 
rings is authorized provided that such attachments and the portion of 
the container to which they are attached are made of weldable steel, 
the carbon content of which may not exceed 0.25 percent.
    (2) Heat treatment is not required after welding or brazing 
weldable low carbon parts to attachments, specified in paragraph (f)(1) 
of this section, of similar material which have been previously welded 
or brazed to the top or bottom of cylinders and properly heat treated, 
provided such subsequent welding or brazing does not produce a 
temperature in excess of 400 deg. F in any part of the top or bottom 
material.
    (g) Wall thickness; wall stress. The wall thickness/wall stress of 
the cylinder must conform to the following:
    (1) The calculated wall stress at 750 pounds per square inch may 
not exceed 35,000 pounds per square inch, or one-half of the minimum 
ultimate strength of the steel as determined in paragraph (l) of this 
section, whichever value is the smaller. The measured wall thickness 
may not include galvanizing or other protective coating.
    (i) Calculation of wall stress must be made by the following 
formula:

S=[P(1.3D2+0.4d2)]/(D2-d2)
Where:

S=Wall stress in pounds per square inch;
P=750 pounds per square inch (minimum test pressure);
D=Outside diameter in inches;
d=Inside diameter in inches.

    (ii) Either D or d must be calculated from the relation D=d + 2t, 
where t=minimum wall thickness.
    (2) Cylinders with a wall thickness less than 0.100 inch, the ratio 
of straight side wall length to outside diameter may not exceed 3.5.
    (3) For cylinders having outside diameter over 5 inches, the 
minimum wall thickness must be 0.087 inch.
    (h) Heat treatment. Each cylinder must be uniformly and properly 
heat treated, prior to tests, by any suitable method in excess of 
1100 deg. F. Heat treatment must be accomplished after all forming and 
welding operations, except that when brazed joints are used, heat 
treatment must follow any forming and welding operations but may be 
done before, during, or after the brazing operations. Liquid quenching 
is not authorized.
    (i) Openings. Standard taper pipe threads required in all openings. 
The length of the opening may not be less than as specified for 
American Standard pipe threads; tapped to gauge; clean cut, even, and 
without checks.
    (j) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test as follows;
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit 
reading of total expansion to an accuracy of either 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat-treatment and previous to the official test may not 
exceed 90 percent of the test pressure.
    (3) Permanent volumetric expansion may not exceed 10 percent of 
total volumetric expansion at test pressure.
    (4) One cylinder out of each lot of 200 or less must be 
hydrostatically tested to at least 750 pounds per square inch. 
Cylinders not so tested must be examined under pressure of between 500 
and 600 pounds per square inch and show no defect. If a hydrostatically 
tested cylinder fails, each cylinder in the lot may be hydrostatically 
tested and those passing are acceptable.
    (k) Leakage test. Cylinders with bottoms closed in by spinning must 
be leakage tested by setting the interior air or gas pressure at not 
less than the service pressure. Any cylinder that leaks must be 
rejected.
    (l) Physical test. A physical test must be conducted as follows;
    (1) The test is required on 2 specimens cut longitudinally from 1 
cylinder or part thereof taken at random out of each lot of 200 or 
less, after heat treatment.
    (2) Specimens must conform to a gauge length of 8 inches with a 
width not over 1\1/2\ inches, a gauge length 2 inches with a width not 
over 1\1/2\ inches, or a gauge length at least 24 times thickness with 
a width not over 6 times thickness is authorized when a cylinder wall 
is not over \3/16\ inch thick.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``offset'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load'') corresponding to the stress at which the 
0.2 percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, 

[[Page 8364]]
the entire stress-strain diagram must be plotted and the yield strength 
determined from the 0.2 offset.
    (iii) For the purpose of strain measurement, the initial strain 
must be set while the specimen is under a stress of 12,000 pounds per 
square inch, the strain indicator reading being set at the calculated 
corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed 1/8 
inch per minute during yield strength determination.
    (m) Elongation. Physical test specimens must show at least a 40 
percent elongation for a 2 inch gauge length or at least a 20 percent 
elongation in other cases. Except that these elongation percentages may 
be reduced numerically by 2 for 2 inch specimens and 1 in other cases 
for each 7,500 pounds per square inch increment of tensile strength 
above 50,000 pounds per square inch to a maximum of four such 
increments.
    (n) Weld tests. Specimens taken across the circumferentially welded 
seam must be cut from one cylinder taken at random from each lot of 200 
or less cylinders after heat treatment and must pass satisfactorily the 
following tests:
    (1) Tensile test. A specimen must be cut from one cylinder of each 
lot of 200 or less, or welded test plate. The specimen must be taken 
from across the major seam and must be prepared and tested in 
accordance with and must meet the requirements of CGA Pamphlet C-3. 
Should this specimen fail to meet the requirements, specimens may be 
taken from two additional cylinders or welded test plates from the same 
lot and tested. If either of the latter specimens fail to meet the 
requirements, the entire lot represented must be rejected.
    (2) Guided bend test. A root bend test specimen must be cut from 
the cylinder or welded test plate, used for the tensile test specified 
in paragraph (n)(1) of this section. Specimens must be prepared and 
tested in accordance with and must meet the requirements of CGA 
Pamphlet C-3.
    (3) Alternate guided-bend test. This test may be used and must be 
as required by CGA Pamphlet C-3. The specimen must be bent until the 
elongation at the outer surface, adjacent to the root of the weld, 
between the lightly scribed gage lines--a to b, must be at least 20 
percent, except that this percentage may be reduced for steels having a 
tensile strength in excess of 50,000 pounds per square inch, as 
provided in paragraph (m) of this section.
    (o) Rejected cylinders. Reheat treatment of rejected cylinders is 
authorized. Subsequent thereto, cylinders must pass all prescribed 
tests to be acceptable. Repair by welding is authorized.
    (p) Porous filling. (1) Cylinders must be filled with a porous 
material in accordance with the following:
    (i) The porous material may not disintegrate or sag when wet with 
solvent or when subjected to normal service;
    (ii) The filling material must be uniform in quality and free of 
voids, except that a well drilled into the filling material beneath the 
valve is authorized if the well is filled with a material of such type 
that the functions of the filling material are not impaired;
    (iii) Overall shrinkage of the filling material is authorized if 
the total clearance between the cylinder shell and filling material, 
after solvent has been added, does not exceed \1/2\ of 1 percent of the 
respective diameter or length but not to exceed \1/8\ inch, measured 
diametrically and longitudinally;
    (iv) The clearance may not impair the functions of the filling 
material;
    (v) The installed filling material must meet the requirements of 
CGA Pamphlet C-12; and
    (vi) Porosity of filling material may not exceed 80 percent except 
that filling material with a porosity of up to 92 percent may be used 
when tested with satisfactory results in accordance with CGA Pamphlet 
C-12.
    (2) When the porosity of each cylinder is not known, a cylinder 
taken at random from a lot of 200 or less must be tested for porosity. 
If the test cylinder fails, each cylinder in the lot may be tested 
individually and those cylinders that pass the test are acceptable.
    (3) For filling that is molded and dried before insertion in 
cylinders, porosity test may be made on sample block taken at random 
from material to be used.
    (4) The porosity of the filling material must be determined; the 
amount of solvent at 70 deg. F for a cylinder:
    (i) Having shell volumetric capacity above 20 pounds water capacity 
(nominal) may not exceed the following:

------------------------------------------------------------------------
                                                               Maximum  
                                                               acetone  
                                                               solvent  
                 Percent porosity of filler                    percent  
                                                                shell   
                                                             capacity by
                                                                volume  
------------------------------------------------------------------------
90 to 92...................................................         43.4
87 to 90...................................................         42.0
83 to 87...................................................         40.0
80 to 83...................................................         38.6
75 to 80...................................................         36.2
70 to 75...................................................         33.8
65 to 70...................................................         31.4
------------------------------------------------------------------------

    (ii) Having volumetric capacity of 20 pounds or less water capacity 
(nominal), may not exceed the following:

------------------------------------------------------------------------
                                                               Maximum  
                                                               acetone  
                                                               solvent  
                 Percent porosity of filler                    percent  
                                                                shell   
                                                             capacity by
                                                                volume  
------------------------------------------------------------------------
90 to 92...................................................         41.8
83 to 90...................................................         38.5
80 to 83...................................................         37.1
75 to 80...................................................         34.8
70 to 75...................................................         32.5
65 to 70...................................................         30.2
------------------------------------------------------------------------

    (q) Tare weight. The tare weight is the combined weight of the 
cylinder proper, porous filling, valve, and solvent, but without 
removable cap.
    (r) Duties of inspector. In addition to the requirements of 
Sec. 178.35, the inspector shall--
    (1) Certify chemical analyses of steel used, signed by manufacturer 
thereof; also verify by check analyses, of samples taken from each heat 
or from 1 out of each lot of 200 or less plates, shells, or tubes used.
    (2) Verify compliance of cylinder shells with all shell 
requirements, inspect inside before closing in both ends, verify heat 
treatment as proper; obtain all samples for all tests and for check 
analyses, witness all tests; verify threads by gauge, report volumetric 
capacity and minimum thickness of wall noted.
    (3) Report percentage of each specified alloying element in the 
steel. Prepare report on manufacture of steel shells in form prescribed 
in Sec. 178.35. Furnish one copy to manufacturer and three copies to 
the company that is to complete the cylinders.
    (4) Determine porosity of filling and tare weights; verify 
compliance of marking with prescribed requirements; obtain necessary 
copies of steel shell reports prescribed in paragraph (b) of this 
section; and furnish complete test reports required by this 
specification to the person who has completed the manufacture of the 
cylinders and, upon request, to the purchaser. The test reports must be 
retained by the inspector for fifteen years from the original test date 
of the cylinder.
    (s) Marking. (1) Tare weight of cylinder, in pounds and ounces, 
must be marked on the cylinder.
    (2) Cylinders, not completed, when delivered must each be marked 
for identification of each lot of 200 or less.
    (3) Markings must be stamped plainly and permanently in locations 
in accordance with the following:
    (i) On shoulders and top heads not less than 0.087 inch thick; or 
    
[[Page 8365]]

    (ii) On neck, valve boss, valve protection sleeve, or similar part 
permanently attached to the top end of cylinder; or
    (iii) On a plate of ferrous material attached to the top of the 
cylinder or permanent part thereof; the plate must be at least \1/16\ 
inch thick, and must be attached by welding, or by brazing at a 
temperature of at least 1,100  deg.F throughout all edges of the plate. 
Sufficient space must be left on the plate to provide for stamping at 
least four (4) retest dates.


Sec. 178.61  Specification 4BW welded steel cylinders with electric-arc 
welded longitudinal seam.

    (a) Type, size and service pressure. A DOT 4BW cylinder is a welded 
type steel cylinder with a longitudinal electric-arc welded seam, a 
water capacity (nominal) not over 1,000 pounds and a service pressure 
at least 225 and not over 500 pounds per square inch gauge. Cylinders 
closed in by spinning process are not authorized.
    (b) Authorized steel. Steel used in the construction of the 
cylinder must conform to the following:
    (1) The body of the cylinder must be constructed of steel 
conforming to the limits specified in Table I of Appendix A to this 
part.
    (2) Material for heads must meet the requirements of paragraph (a) 
of this section or be open hearth, electric or basic oxygen carbon 
steel of uniform quality. Content percent may not exceed the following: 
Carbon 0.25, Manganese 0.60, Phosphorus 0.045, Sulfur 0.050. Heads must 
be hemispherical or ellipsoidal in shape with a maximum ratio of 2.1. 
If low carbon steel is used, the thickness of such heads must be 
determined by using a maximum wall stress of 24,000 p.s.i. in the 
formula described in paragraph (f)(1) of this section.
    (c) Identification of material. Material must be identified by any 
suitable method.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart and the following:
    (1) No defect is permitted that is likely to weaken the finished 
cylinder appreciably. A reasonably smooth and uniform surface is 
required. Exposed bottom welds on cylinders over 18 inches long must be 
protected by footrings. Minimum thickness of heads may not be less than 
90 percent of the required thickness of the sidewall. Heads must be 
concave to pressure.
    (2) Circumferential seams must be by electric-arc welding. Joints 
must be butt with one member offset (joggle butt) or lap with minimum 
overlap of at least four times nominal sheet thickness.
    (3) Longitudinal seams in shells must conform to the following:
    (i) Longitudinal electric-arc welded seams must be of the butt 
welded type. Welds must be made by a machine process including 
automatic feed and welding guidance mechanisms. Longitudinal seams must 
have complete joint penetration, and must be free from undercuts, 
overlaps or abrupt ridges or valleys. Misalignment of mating butt edges 
may not exceed \1/6\ of nominal sheet thickness or \1/32\ inch 
whichever is less. All joints with nominal sheet thickness up to and 
including \1/8\ inch must be tightly butted. When nominal sheet 
thickness is greater than \1/8\ inch, the joint must be gapped with 
maximum distance equal to one-half the nominal sheet thickness or \1/
32\ inch whichever is less. Joint design, preparation and fit-up must 
be such that requirements of this paragraph (d) are satisfied.
    (ii) Maximum joint efficiency must be 1.0 when each seam is 
radiographed completely. Maximum joint efficiency must be 0.90 when one 
cylinder from each lot of 50 consecutively welded cylinders is spot 
radiographed. In addition, one out of the first five cylinders welded 
following a shut down of welding operations exceeding four hours must 
be spot radiographed. Spot radiographs, when required, must be made of 
a finished welded cylinder and must include the girth weld for 2 inches 
in both directions from the intersection of the longitudinal and girth 
welds and include at least 6 inches of the longitudinal weld. Maximum 
joint efficacy of 0.75 must be permissible without radiography.
    (4) Welding procedures and operators must be qualified in 
accordance with CGA Pamphlet C-3.
    (e) Welding of attachments. The attachment to the tops and bottoms 
only of cylinders by welding of neckrings, footrings, handles, bosses, 
pads and valve protection rings is authorized provided that such 
attachments and the portion of the container to which they are attached 
are made of weldable steel, the carbon content of which may not exceed 
0.25 percent.
    (f) Wall thickness. For outside diameters over 6 inches the minimum 
wall thickness must be 0.078 inch. For a cylinder with a wall thickness 
less than 0.100 inch, the ratio of tangential length to outside 
diameter may not exceed 4 to 1 (4:1). In any case the minimum wall 
thickness must be such that the wall stress calculated by the formula 
listed in paragraph (f)(4) of this section may not exceed the lesser 
value of any of the following:
    (1) The value referenced in paragraph (b) of this section for the 
particular material under consideration.
    (2) One-half of the minimum tensile strength of the material 
determined as required in paragraph (m) of this section.
    (3) 35,000 pounds per square inch.
    (4) Stress must be calculated by the following formula:

S=[2P(1.3D2+0.4d2)]/[E(D2-d2)]

where:

S=wall stress, p.s.i.;
P=service pressure, p.s.i.;
D=outside diameter, inches;
d=inside diameter, inches;
E=joint efficiency of the longitudinal seam (from paragraph (d) of this 
section).

    (g) Heat treatment. Each cylinder must be uniformly and properly 
heat treated prior to test by the applicable method referenced in 
paragraph (b) of this section. Heat treatment must be accomplished 
after all forming and welding operations. Heat treatment is not 
required after welding or brazing of weldable low carbon parts to 
attachments of similar material which have been previously welded to 
the top or bottom of cylinders and properly heat treated, provided such 
subsequent welding or brazing does not produce a temperature in excess 
of 400 deg. F in any part of the top or bottom material.
    (h) Openings in cylinders. Openings in the cylinder must conform to 
the following:
    (1) All openings must be in the heads or bases.
    (2) Openings in cylinders must be provided with adequate fittings, 
bosses, or pads, integral with or securely attached to the cylinder by 
welding.
    (3) Threads must comply with the following:
    (i) Threads must be clean cut and to gauge.
    (ii) Taper threads must be of length not less than as specified for 
American Standard Taper Pipe threads.
    (iii) Straight threads, having at least 4 engaged threads, to have 
tight fit and calculated shear strength at least 10 times the test 
pressure of the cylinder; gaskets required, adequate to prevent 
leakage.
    (4) Closure of fittings, boss or pads must be adequate to prevent 
leakage.
    (i) Hydrostatic test. Cylinders must withstand a hydrostatic test, 
as follows:
    (1) The test must be by water-jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
readings to an 

[[Page 8366]]
accuracy of 1 percent. The expansion gauge must permit readings of 
total volumetric expansion to an accuracy either of 1 percent or 0.1 
cubic centimeter.
    (2) Pressure must be maintained for at least 30 seconds and 
sufficiently longer to ensure complete expansion. Any internal pressure 
applied after heat treatment and previous to the official test may not 
exceed 90 percent of the test pressure.
    (3) Permanent volumetric expansion may not exceed 10 percent of the 
total volumetric expansion at test pressure.
    (4) Cylinders must be tested as follows:
    (i) At least 1 cylinder selected at random out of each lot of 200 
or less must be tested as outlined in paragraphs (i)(1), (i)(2), and 
(i)(3) of this section to at least two times service pressure.
    (ii) All cylinders not tested as outlined in paragraph (i)(4)(i) of 
this section must be examined under pressure of at least two times 
service pressure and show no defect.
    (5) One finished cylinder selected at random out of each lot of 500 
or less successively produced must be hydrostatically tested to 4 times 
service pressure without bursting.
    (j) Physical tests. Cylinders must be subjected to a physical test 
as follows:
    (1) Specimens must be taken from one cylinder after heat treatment 
and chosen at random from each lot of 200 or less, as follows:
    (i) Body specimen. One specimen must be taken longitudinally from 
the body section at least 90 degrees away from the weld.
    (ii) Head specimen. One specimen must be taken from either head on 
a cylinder when both heads are made of the same material. However, if 
the two heads are made of differing materials, a specimen must be taken 
from each head.
    (iii) If due to welded attachments on the top head there is 
insufficient surface from which to take a specimen, it may be taken 
from a representative head of the same heat treatment as the test 
cylinder.
    (2) Specimens must conform to the following:
    (i) A gauge length of 8 inches with a width not over 1\1/2\ inches, 
a gauge length of 2 inches with a width not over 1\1/2\ inches, or a 
gauge length at least 24 times thickness with a width not over 6 times 
thickness is authorized when a cylinder wall is not over \3/16\ inch 
thick.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within 1 inch of each end of the reduced 
section.
    (iii) When size of the cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold, by pressure only, not by blows 
when specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical tests detailed information 
in regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by either the ``off-set'' 
method or the ``extension under load'' method as prescribed in ASTM 
Standard E8-78.
    (ii) In using the ``extension under load'' method, the total strain 
(or ``extension under load''), corresponding to the stress at which the 
0.2-percent permanent strain occurs may be determined with sufficient 
accuracy by calculating the elastic extension of the gauge length under 
appropriate load and adding thereto 0.2 percent of the gauge length. 
Elastic extension calculations must be based on an elastic modulus of 
30,000,000. In the event of controversy, the entire stress-strain 
diagram must be plotted and the yield strength determined from the 0.2-
percent offset.
    (iii) For the purpose of strain measurement, the initial strain 
reference must be set while the specimen is under a stress of 12,000 
pounds per square inch and the strain indicator reading being set at 
the calculated corresponding strain.
    (iv) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (k) Elongation. Physical test specimens must show at least a 40 
percent elongation for a 2-inch gauge length or at least a 20 percent 
elongation in other cases. Except that these elongation percentages may 
be reduced numerically by 2 for 2-inch specimens and by 1 in other 
cases for each 7,500 pounds per square inch increment of tensile 
strength above 50,000 pounds per square inch to a maximum of four 
increments.
    (l) Tests of welds. Welds must be subjected to the following tests:
    (1) Tensile test. A specimen must be cut from one cylinder of each 
lot of 200 or less. The specimen must be taken from across the 
longitudinal seam and must be prepared and tested in accordance with 
and must meet the requirements of CGA Pamphlet C-3.
    (2) Guided bend test. A root test specimen must be cut from the 
cylinder used for the tensile test specified in paragraph (l)(1) of 
this section. Specimens must be taken from across the longitudinal seam 
and must be prepared and tested in accordance with and must meet the 
requirements of CGA Pamphlet C-3.
    (3) Alternate guided bend test. This test may be used and must be 
as required by CGA Pamphlet C-3. The specimen must be bent until the 
elongation at the outer surface, adjacent to the root of the weld, 
between the lightly scribed gauge lines a to b, must be at least 20 
percent, except that this percentage may be reduced for steels having a 
tensile strength in excess of 50,000 pounds per square inch, as 
provided in paragraph (k) of this section.
    (m) Radiographic examination. Welds of the cylinders must be 
subjected to a radiographic examination as follows:
    (1) Radiographic inspection must conform to the techniques and 
acceptability criteria set forth in CGA Pamphlet C-3. When fluoroscopic 
inspection is used, permanent film records need not be retained.
    (2) Should spot radiographic examination fail to meet the 
requirements of paragraph (m)(1) of this section, two additional welds 
from the same lot of 50 cylinders or less must be examined, and if 
either of these fail to meet the requirements, each cylinder must be 
examined as previously outlined; only those passing are acceptable.
    (n) Rejected cylinders. (1) Unless otherwise stated, if a sample 
cylinder or specimen taken from a lot of cylinders fails the prescribed 
test, then two additional specimens must be selected from the same lot 
and subjected to the prescribed test. If either of these fails the 
test, then the entire lot must be rejected.
    (2) Reheat treatment of rejected cylinders is authorized. 
Subsequent thereto, cylinders must pass all prescribed tests to be 
acceptable. Repair of welded seams by welding is authorized provided 
that all defective metal is cut away and the joint is rewelded as 
prescribed for original welded joints.
    (o) Markings. Markings must be stamped plainly and permanently in 
any of the following locations on the cylinder:
    (1) On shoulders and top heads when they are not less than 0.087-
inch thick.
    (2) On a metal plate attached to the top of the cylinder or 
permanent part thereof; sufficient space must be left on the plate to 
provide for stamping at least six retest dates; the plate must be at 

[[Page 8367]]
least \1/16\-inch thick and must be attached by welding, or by brazing. 
The brazing rod is to melt at a temperature of 1100 deg. F. Welding or 
brazing must be along all the edges of the plate.
    (3) On the neck, valve boss, valve protection sleeve, or similar 
part permanently attached to the top of the cylinder.
    (4) On the footring permanently attached to the cylinder, provided 
the water capacity of the cylinder does not exceed 25 pounds.
    (p) Inspector's report. In addition to the information required by 
Sec. 178.35, the inspector's report must indicate the type and amount 
of radiography.


Sec. 178.65  Specification 39 non-reusable (non-refillable) cylinders.

    (a) Type, size, service pressure, and test pressure. A DOT 39 
cylinder is a seamless, welded, or brazed cylinder with a service 
pressure not to exceed 80 percent of the test pressure. Spherical 
pressure vessels are authorized and covered by references to cylinders 
in this specification.
    (1) Size limitation. Maximum water capacity may not exceed:
    (i) 55 pounds (1,526 cubic inches) for a service pressure of 500 
p.s.i.g. or less, and
    (ii) 10 pounds (277 cubic inches) for a service pressure in excess 
of 500 p.s.i.g.
    (2) Test pressure. The minimum test pressure is the maximum 
pressure of contents at 130 deg. F or 180 p.s.i.g. whichever is 
greater.
    (3) Pressure of contents. The term ``pressure of contents'' as used 
in this specification means the total pressure of all the materials to 
be shipped in the cylinder.
    (b) Material; steel or aluminum. The cylinder must be constructed 
of either steel or aluminum conforming to the following requirements:
    (1) Steel. (i) The steel analysis must conform to the following:

------------------------------------------------------------------------
                                                   Ladle        Check   
                                                  analysis     analysis 
------------------------------------------------------------------------
Carbon, maximum percent.......................         0.12         0.15
Phosphorus, maximum percent...................         0.04         0.05
Sulfur, maximum percent.......................         0.05         0.06
------------------------------------------------------------------------

    (ii) For a cylinder made of seamless steel tubing with integrally 
formed ends, hot drawn, and finished, content percent for the following 
may not exceed: Carbon, 0.55; phosphorous, 0.045; sulfur, 0.050.
    (iii) For non-heat treated welded steel cylinders, adequately 
killed deep drawing quality steel is required.
    (iv) Longitudinal or helical welded cylinders are not authorized 
for service pressures in excess of 500 p.s.i.g.
    (2) Aluminum. Aluminum is not authorized for service pressures in 
excess of 500 p.s.i.g. The analysis of the aluminum must conform to the 
Aluminum Association standard for alloys 1060, 1100, 1170, 3003, 5052, 
5086, 5154, 6061, and 6063 as specified in its publication entitled 
``Aluminum Standards and Data'' (7th edition dated June 1982).
    (3) Unauthorized material. Material with seams, cracks, 
laminations, or other injurious defects not permitted.
    (4) Identification. Material used must be identified by any 
suitable method.
    (c) Manufacture. (1) General manufacturing requirements are as 
follows:
    (i) The surface finish must be uniform and reasonably smooth.
    (ii) Inside surfaces must be clean, dry, and free of loose 
particles.
    (iii) No defect of any kind is permitted if it is likely to weaken 
a finished cylinder.
    (2) Requirements for seams:
    (i) Brazing is not authorized on aluminum cylinders.
    (ii) Brazing material must have a melting point of not lower than 
1,000 deg. F.
    (iii) Brazed seams must be assembled with proper fit to ensure 
complete penetration of the brazing material throughout the brazed 
joint.
    (iv) Minimum width of brazed joints must be at least four times the 
thickness of the shell wall.
    (v) Brazed seams must have design strength equal to or greater than 
1.5 times the minimum strength of the shell wall.
    (vi) Welded seams must be properly aligned and welded by a method 
that provides clean, uniform joints with adequate penetration.
    (vii) Welded joints must have a strength equal to or greater than 
the minimum strength of the shell material in the finished cylinder.
    (3) Attachments to the cylinder are permitted by any means which 
will not be detrimental to the integrity of the cylinder. Welding or 
brazing of attachments to the cylinder must be completed prior to all 
pressure tests.
    (4) Welding procedures and operators must be qualified in 
accordance with CGA Pamphlet C-3.
    (d) Wall thickness. The minimum wall thickness must be such that 
the wall stress at test pressure does not exceed the yield strength of 
the material of the finished cylinder wall. Calculations must be made 
by the following formulas:
    (1) Calculation of the stress for cylinders must be made by the 
following formula:

S=[P(1.3D2+0.4d2)]/(D2-d2)

where:

S=Wall stress, in p.s.i.;
P=Test pressure;
D=Outside diameter, in inches;
d=Inside diameter, in inches.

    (2) Calculation of the stress for spheres must be made by the 
following formula:

S=PD/4t

Where:
S=Wall stress, in p.s.i.;
P=Test pressure;
D=Outside diameter, in inches;
t=Minimum wall thickness, in inches.

    (e) Openings and attachments. Openings and attachments must conform 
to the following:
    (1) Openings and attachments are permitted on heads only.
    (2) All openings and their reinforcements must be within an 
imaginary circle, concentric to the axis of the cylinder. The diameter 
of the circle may not exceed 80 percent of the outside diameter of the 
cylinder. The plane of the circle must be parallel to the plane of a 
circumferential weld and normal to the long axis of the cylinder.
    (3) Unless a head has adequate thickness, each opening must be 
reinforced by a securely attached fitting, boss, pad, collar, or other 
suitable means.
    (4) Material used for welded openings and attachments must be of 
weldable quality and compatible with the material of the cylinder.
    (f) Pressure tests. (1) Each cylinder must be tested at an internal 
pressure of at least the test pressure and must be held at that 
pressure for at least 30 seconds.
    (i) The leakage test must be conducted by submersion under water or 
by some 

[[Page 8368]]
other method that will be equally sensitive.
    (ii) If the cylinder leaks, evidences visible distortion, or any 
other defect, while under test, it must be rejected (see paragraph (h) 
of this section).
    (2) One cylinder taken from the beginning of each lot, and one from 
each 1,000 or less successively produced within the lot thereafter, 
must be hydrostatically tested to destruction. The entire lot must be 
rejected (see paragraph (h) of this section) if:
    (i) A failure occurs at a gage pressure less than 2.0 times the 
test pressure;
    (ii) A failure initiates in a braze or a weld or the heat affected 
zone thereof;
    (iii) A failure is other than in the sidewall of a cylinder 
longitudinal with its long axis; or
    (iv) In a sphere, a failure occurs in any opening, reinforcement, 
or at a point of attachment.
    (3) A ``lot'' is defined as the quantity of cylinders successively 
produced per production shift (not exceeding 10 hours) having identical 
size, design, construction, material, heat treatment, finish, and 
quality.
    (g) Flattening test. One cylinder must be taken from the beginning 
of production of each lot (as defined above) and subjected to a 
flattening test as follows:
    (1) The flattening test must be made on a cylinder that has been 
tested at test pressure.
    (2) A ring taken from a cylinder may be flattened as an alternative 
to a test on a complete cylinder. The test ring may not include the 
heat affected zone or any weld. However, for a sphere, the test ring 
may include the circumferential weld if it is located at a 45 degree 
angle to the ring, +/-5 degrees.
    (3) The flattening must be between 60 degrees included-angle, wedge 
shaped knife edges, rounded to a 0.5 inch radius.
    (4) Cylinders and test rings may not crack when flattened so that 
their outer surfaces are not more than six times wall thickness apart 
when made of steel or not more than ten times wall thickness apart when 
made of aluminum.
    (5) If any cylinder or ring cracks when subjected to the specified 
flattening test, the lot of cylinders represented by the test must be 
rejected (see paragraph (h) of this section).
    (h) Rejected cylinders. Rejected cylinders must conform to the 
following requirements:
    (1) If the cause for rejection of a lot is determinable, and if by 
test or inspection defective cylinders are eliminated from the lot, the 
remaining cylinders must be qualified as a new lot under paragraphs (f) 
and (g) of this section.
    (2) Repairs to welds are permitted. Following repair, a cylinder 
must pass the pressure test specified in paragraph (f) of this section.
    (3) If a cylinder made from seamless steel tubing fails the 
flattening test described in paragraph (g) of this section, suitable 
uniform heat treatment must be used on each cylinder in the lot. All 
prescribed tests must be performed subsequent to this heat treatment.
    (i) Markings. (1) The markings required by this section must be 
durable and waterproof. The requirements of Sec. 173.24 (c)(1) (ii) and 
(iv) of this subchapter and Sec. 178.35(h) do not apply to this 
section.
    (2) Required markings are as follow:
    (i) DOT-39.
    (ii) NRC.
    (iii) The service pressure.
    (iv) The test pressure.
    (v) The registration number (M****) of the manufacturer.
    (vi) The lot number.
    (vii) The date of manufacture if the lot number does not establish 
the date of manufacture.
    (viii) The following statement: Federal law forbids transportation 
if refilled-penalty up to $500,000 fine and 5 years imprisonment (49 
U.S.C. 5124).
    (3) The markings required by paragraphs (i)(2)(i) through (i)(2)(v) 
of this section must be in numbers and letters at least \1/8\ inch high 
and displayed sequentially. For example:

DOT-39 NRC 250/500 M1001.

    (4) No person may mark any cylinder with the specification 
identification ``DOT-39'' unless it was manufactured in compliance with 
the requirements of this section and its manufacturer has a 
registration number (M****) from the Associate Administrator.


Sec. 178.68  Specification 4E welded aluminum cylinders.

    (a) Type, size and service pressure. A DOT 4E cylinder is a welded 
aluminum cylinder with a water capacity (nominal) of not over 1,000 
pounds and a service pressure of at least 250 to not over 500 pounds 
per square inch. The cylinder must be constructed of not more than two 
seamless drawn shells with no more than one circumferential weld. The 
circumferential weld may not be closer to the point of tangency of the 
cylindrical portion with the shoulder than 20 times the cylinder wall 
thickness. Cylinders or shells closed in by spinning process and 
cylinders with longitudinal seams are not authorized.
    (b) Authorized material. The cylinder must be constructed of 
aluminum of uniform quality. The following chemical analyses are 
authorized:

                     Table 1.--Authorized Materials                     
------------------------------------------------------------------------
                                               Chemical analysis--limits
                 Designation                      in percent 5154 \1\   
------------------------------------------------------------------------
Iron plus silicon............................  0.45 maximum.            
Copper.......................................  0.10 maximum.            
Manganese....................................  0.10 maximum.            
Magnesium....................................  3.10/3.90.               
Chromium.....................................  0.15/0.35.               
Zinc.........................................  0.20 maximum.            
Titanium.....................................  0.20 maximum.            
Others, each.................................  0.05 maximum.            
Others, total................................  0.15 maximum.            
Aluminum.....................................  Remainder.               
------------------------------------------------------------------------
\1\ Analysis must regularly be made only for the elements specifically  
  mentioned in this table. If, however, the presence of other elements  
  is indicated in the course of routine analysis, further analysis      
  should be made to determine conformance with the limits specified for 
  other elements.                                                       


[[Page 8369]]

    (c) Identification. Material must be identified by any suitable 
method that will identify the alloy and manufacturer's lot number.
    (d) Manufacture. Cylinders must be manufactured using equipment and 
processes adequate to ensure that each cylinder produced conforms to 
the requirements of this subpart. No defect is permitted that is likely 
to weaken the finished cylinder appreciably. A reasonably smooth and 
uniform surface finish is required. All welding must be by the gas 
shielded arc process.
    (e) Welding. The attachment to the tops and bottoms only of 
cylinders by welding of neckrings or flanges, footrings, handles, 
bosses and pads and valve protection rings is authorized. However, such 
attachments and the portion of the cylinder to which it is attached 
must be made of weldable aluminum alloys.
    (f) Wall thickness. The wall thickness of the cylinder must conform 
to the following:
    (1) The minimum wall thickness of the cylinder must be 0.140 inch. 
In any case, the minimum wall thickness must be such that calculated 
wall stress at twice service pressure may not exceed the lesser value 
of either of the following:
    (i) 20,000 pounds per square inch.
    (ii) One-half of the minimum tensile strength of the material as 
required in paragraph (m) of this section.
    (2) Calculation must be made by the following formula:

S=[P(1.3D2+0.4d2)]/(D2-d2)

where:

S=Wall stress in pounds per square inch;
P=Minimum test pressure prescribed for water jacket test;
D=Outside diameter in inches;
d=Inside diameter in inches.

    (3) Minimum thickness of heads and bottoms may not be less than the 
minimum required thickness of the side wall.
    (g) Opening in cylinder. Openings in cylinders must conform to the 
following:
    (1) All openings must be in the heads or bases.
    (2) Each opening in cylinders, except those for safety devices, 
must be provided with a fitting, boss, or pad, securely attached to 
cylinder by welding by inert gas shielded arc process or by threads. If 
threads are used, they must comply with the following:
    (i) Threads must be clean-cut, even, without checks and cut to 
gauge.
    (ii) Taper threads to be of length not less than as specified for 
American Standard taper pipe threads.
    (iii) Straight threads, having at least 4 engaged threads, to have 
tight fit and calculated shear strength at least 10 times the test 
pressure of the cylinder; gaskets required, adequate to prevent 
leakage.
    (3) Closure of a fitting, boss, or pad must be adequate to prevent 
leakage.
    (h) Hydrostatic test. Each cylinder must successfully withstand a 
hydrostatic test, as follows:
    (1) The test must be by water jacket, or other suitable method, 
operated so as to obtain accurate data. The pressure gauge must permit 
reading to an accuracy of 1 percent. The expansion gauge must permit a 
reading of the total expansion to an accuracy either of 1 percent or 
0.1 cubic centimeter.
    (2) Pressure of 2 times service pressure must be maintained for at 
least 30 seconds and sufficiently longer to insure complete expansion. 
Any internal pressure applied previous to the official test may not 
exceed 90 percent of the test pressure. If, due to failure of the test 
apparatus, the test pressure cannot be maintained, the test may be 
repeated at a pressure increased by 10 percent over the pressure 
otherwise specified.
    (3) Permanent volumetric expansion may not exceed 12 percent of 
total volumetric expansion at test pressure.
    (4) Cylinders having a calculated wall stress of 18,000 pounds per 
square inch or less at test pressure may be tested as follows:
    (i) At least one cylinder selected at random out of each lot of 200 
or less must be tested in accordance with paragraphs (h)(1), (h)(2), 
and (h)(3) of this section.
    (ii) All cylinders not tested as provided in paragraph (h)(4)(i) of 
this section must be examined under pressure of at least 2 times 
service pressure and show no defect.
    (5) One finished cylinder selected at random out of each lot of 
1,000 or less must be hydrostatically tested to 4 times the service 
pressure without bursting. Inability to meet this requirement must 
result in rejection of the lot.
    (i) Flattening test. After hydrostatic testing, a flattening test 
is required on one section of a cylinder, taken at random out of each 
lot of 200 or less as follows:
    (1) If the weld is not at midlength of the cylinder, the test 
section must be no less in width than 30 times the cylinder wall 
thickness. The weld must be in the center of the section. Weld 
reinforcement must be removed by machining or grinding so that the weld 
is flush with the exterior of the parent metal. There must be no 
evidence of cracking in the sample when it is flattened between flat 
plates to no more than 6 times the wall thickness.
    (2) If the weld is at midlength of the cylinder, the test may be 
made as specified in paragraph (i)(1)(i) of this section or must be 
made between wedge shaped knife edges (60 deg. angle) rounded to a \1/
2\-inch radius. There must be no evidence of cracking in the sample 
when it is flattened to no more than 6 times the wall thickness.
    (j) Physical test. A physical test must be conducted to determine 
yield strength, tensile strength, elongation, and reduction of area of 
material as follows:
    (1) The test is required on 2 specimens cut from one cylinder or 
part thereof taken at random out of each lot of 200 or less.
    (2) Specimens must conform to the following:
    (i) A gauge length of 8 inches with a width not over 1\1/2\ inches, 
a gauge length of 2 inches with a width not over 1\1/2\ inches.
    (ii) The specimen, exclusive of grip ends, may not be flattened. 
Grip ends may be flattened to within 1 inch of each end of the reduced 
section.
    (iii) When size of cylinder does not permit securing straight 
specimens, the specimens may be taken in any location or direction and 
may be straightened or flattened cold, by pressure only, not by blows; 
when specimens are so taken and prepared, the inspector's report must 
show in connection with record of physical test detailed information in 
regard to such specimens.
    (iv) Heating of a specimen for any purpose is not authorized.
    (3) The yield strength in tension must be the stress corresponding 
to a permanent strain of 0.2 percent of the gauge length. The following 
conditions apply:
    (i) The yield strength must be determined by the ``offset'' method 
as prescribed in ASTM Standard E8-78.
    (ii) Cross-head speed of the testing machine may not exceed \1/8\ 
inch per minute during yield strength determination.
    (k) Acceptable results for physical tests. An acceptable result of 
the physical test requires an elongation to at least 7 percent and 
yield strength not over 80 percent of tensile strength.
    (l) Weld tests. Welds of the cylinder are required to successfully 
pass the following tests:
    (1) Reduced section tensile test. A specimen must be cut from the 
cylinder used for the physical tests specified in paragraph (j) of this 
section. The specimen must be taken from across the seam, edges must be 
parallel for a distance of approximately 2 inches on 

[[Page 8370]]
either side of the weld. The specimen must be fractured in tension. The 
apparent breaking stress calculated on the minimum wall thickness must 
be at least equal to 2 times the stress calculated under paragraph 
(f)(2) of this section, and in addition must have an actual breaking 
stress of at least 30,000 pounds per square inch. Should this specimen 
fail to meet the requirements, specimens may be taken from 2 additional 
cylinders from the same lot and tested. If either of the latter 
specimens fails to meet requirements, the entire lot represented must 
be rejected.
    (2) Guided bend test. A bend test specimen must be cut from the 
cylinder used for the physical tests specified in paragraph (j) of this 
section. Specimen must be taken across the seam, must be 1\1/2\ inches 
wide, edges must be parallel and rounded with a file, and back-up 
strip, if used, must be removed by machining. The specimen must be bent 
to refusal in the guided bend test jig illustrated in paragraph 6.10 of 
CGA Pamphlet C-3. The root of the weld (inside surface of the cylinder) 
must be located away from the ram of the jig. No specimen must show a 
crack or other open defect exceeding \1/8\ inch in any direction upon 
completion of the test. Should this specimen fail to meet the 
requirements, specimens may be taken from each of 2 additional 
cylinders from the same lot and tested. If either of the latter 
specimens fail to meet requirements, the entire lot represented must be 
rejected.
    (m) Rejected cylinders. Repair of welded seams is authorized. 
Acceptable cylinders must pass all prescribed tests.
    (n) Inspector's report. In addition to the information required by 
Sec. 178.35, the record of chemical analyses must also include 
applicable information on iron, titanium, zinc, and magnesium used in 
the construction of the cylinder.

    Issued in Washington, DC on February 12, 1996, under authority 
delegated in 49 CFR Part 106.
Alan I. Roberts,
Associate Administrator for Hazardous Materials Safety.
[FR Doc. 96-3554 Filed 3-1-96; 8:45 am]
BILLING CODE 4910-60-P