MIL-STD-1411B
f. Cylinders requiring external surface maintenance.
5.3.1 Periodic testing. Cylinders in maintenance for periodic testing are generally cylinders with expired or invalid periodic test dates. Exceptions would be a requirement for 100 percent testing specified in a reconditioning contract or a cylinder that has undergone rebuild procedures. Cylinders shall be subjected to hydrostatic testing, UE, or external visual inspection. Acetylene cylinders shall be examined both externally and internally for requalification as specified herein.
5.3.1.1 Hydrostatic test and UE. The hydrostatic test shall be performed in accordance with 49 CFR. To pass the hydrostatic test, a DOT 3A or DOT 3AA cylinder subjected to 5/3 times its marked service pressure internally shall have a permanent expansion that is less than 10 percent of its total expansion. The cylinder elastic expansion (EE) will be its total expansion less its permanent expansion. Low-pressure welded cylinders shall undergo hydrostatic testing at
two times the marked service pressure. Permanent volumetric expansion must not exceed 10 percent of the total volumetric expansion. UE may be performed in lieu of the above hydrostatic testing by an approved facility with a DOT special permit for DOT 3A and DOT 3AA cylinders, with the exception of cylinders manufactured in accordance with MS26545. The UE testing criteria shall at a minimum meet that of DOT-SP 14313. DOT 4B, DOT 4BA, DOT 4BW, and DOT 4E cylinders used in services such as LPG, fluorocarbon refrigerants, and fuel gas mixtures or as listed in 49 CFR 173.34g may be tested by the modified hydrostatic method at two times
the marked service pressure and examined for leaks or other defects without measurement of the volumetric expansion. Cylinders approved by the modified hydrostatic method shall have a retest period of seven years and shall be permanently marked with the symbol "S" after the test date. The hydrostatic test shall always be preceded by a droplight test (see 5.3.2.2). Any cylinder displaying contamination such as grease, corrosion, or oxidation deposits shall be scheduled for cleaning or mechanical removal of the offending deposits before hydrostatic testing. Cylinders that fail droplight test procedures, hydrostatic test requirements, or UE shall be rejected, marked condemned, and returned to the government agency for disposal. Cylinders passing internal visual examination and cylinders approved in hydrostatic testing shall be
drained and dried in accordance with 5.3.2.5 and immediately revalved or sealed with a plug and gasket.
5.3.1.1.1 Special filling limit test. DOT 3A and DOT 3AA cylinders that meet the requirements of the 49 CFR 173.302 may be marked with a "+" sign and filled to a pressure
10 percent above the marked service pressure. These requirements, including a wall stress analysis, shall be made at each retest of a given cylinder. High-pressure cylinders DOT 3A and DOT 3AA, size 9 inches x 51 inches with a nominal water capacity of 2,640 cubic inches may be tested for special filling limits 10 percent above the marked service pressure (see special filling limits 49 CFR 173.302 and as specified herein). In order to approve a cylinder for this special filling limit using UE, the cylinder must meet or exceed the pertinent requirements stated in the special provisions of DOT-SP 14313. Approved cylinders shall be marked permanently by a "+" sign following the last periodic hydrostatic test or UE date. If a cylinder has been in service at
the special filling limit and marked with a "+" sign and is retested by regular hydrostatic test or fails to meet the requirements of the special provisions in DOT-SP 14313 when reexamined ultrasonically, the date is not to be followed by a "+" sign and it shall be returned to service at
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