[Code of Federal Regulations]
[Title 49, Volume 2]
[Revised as of October 1, 2006]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR178.56]

[Page 872-875]
 
                        TITLE 49--TRANSPORTATION
 
   CHAPTER I--PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION, 
                      DEPARTMENT OF TRANSPORTATION
 
PART 178_SPECIFICATIONS FOR PACKAGINGS--Table of Contents
 
                 Subpart C_Specifications for Cylinders
 
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 psig. 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 C-3 (IBR, see Sec.  171.7 of this subchapter).
    (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 psi.

[[Page 873]]

    (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 psi;
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 psig, 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

[[Page 874]]

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 E 8 
(IBR, see Sec.  171.7 of this subchapter).
    (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 psi 
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 specimens and by 1 in other cases 
for each 7,500 psi increment of tensile strength above 50,000 psi 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 psi, as provided in paragraph (k) of this 
section.

[[Page 875]]

    (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.

[Amdt. 178-114, 61 FR 25942, May 23, 1996, as amended at 66 FR 45386, 
Aug. 28, 2001; 67 FR 51653, Aug. 8, 2002; 68 FR 75748, 75749, Dec. 31, 
2003]