[Code of Federal Regulations]
[Title 49, Volume 2]
[Revised as of October 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR178.38]

[Page 780-782]
 
                        TITLE 49--TRANSPORTATION
 
 CHAPTER I--RESEARCH AND SPECIAL PROGRAMS ADMINISTRATION, DEPARTMENT OF 
                             TRANSPORTATION
 
PART 178_SPECIFICATIONS FOR PACKAGINGS--Table of Contents
 
                 Subpart C_Specifications for Cylinders
 
Sec.  178.38  Specification 3B seamless steel cylinders.

    (a) Type, size, and service pressure. A DOT 3B cylinder is 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 psig.
    (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 psig 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 psi. 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 psi;
P = at least two times service pressure or 450 psig, 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

[[Page 781]]

repeated at a pressure increased by 10 percent or 100 psig, 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 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 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; 
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 E 8 
(incorporated by reference; 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 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.
    (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

[[Page 782]]

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 psig 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.

[Amdt. 178-114, 61 FR 25942, May 23, 1996, as amended by 66 FR 45185, 
45386-45388, Aug. 28, 2001; 67 FR 51652, Aug. 8, 2002]