[Code of Federal Regulations]
[Title 49, Volume 2]
[Revised as of October 1, 2007]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR178.36]
[Page 835-838]
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. 178.36 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 psig.
(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 psig, 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 = A1 P/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-psig.
[[Page 836]]
(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 psig 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 psig. 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 psi;
P = minimum test pressure prescribed for water jacket test or 450 psig
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 psig, 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.
[[Page 837]]
(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,
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 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 must
be set while the specimen is under a stress of 12,000 psig 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
[[Page 838]]
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.
[Amdt. 178-114, 61 FR 25942, May 23, 1996, as amended at 62 FR 51561,
Oct. 1, 1997; 66 FR 45185, 45386-45387, Aug. 28, 2001; 67 FR 51652, Aug.
8, 2002; 68 FR 75748, Dec. 31, 2003]