MIL-STD-1411 Inspection And Maintenance Of Compressed Gas CylindersThis standard defines the requirements and procedures for the inspection, maintenance, and charging of government-owned cylinders by gas suppliers. This standard is intended to assure that the cylinders are serviced to meet safety standards and to assure that the quality of the gas supplied is not degraded by a government container. This standard is also applicable to cylinders that require reconditioning, repair, and rebuilding to assure a level of renewal that meets the needs of the government and industry in gas handling. This standard is also to be a guide when cylinders are sorted, graded, and classified for storage, salvage, or disposal in depot facilities.

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MIL-STD-1411B

3.24  Periodic test status.  Cylinders are periodically tested by hydrostatic test procedures, UE or subjected to an external visual examination.  Cylinders should undergo periodic testing and hydrostatic testing according to 49 CFR 173.34.  Periodic UE can be performed in lieu of hydrostatic testing when allowed by DOT special permit.  The periodic cycle for UE is the same as that for hydrostatic testing for any given cylinder and gas service. The government permits external visual examination of low-pressure cylinder services for LPGs and some fluorocarbon gas cylinders.  These cylinders are permanently marked with the letter "E" after the date of the inspection.  Certain low-pressure cylinders may be retested after 12 years, then every 7 years by the modified hydrostatic test method with the test followed by the symbol "S".

3.25  Permanent and liquefied gases.  A permanent gas is defined as a compressed gas that will not liquefy between 25 psig and 2500 psig at 70 °F.  These gases have boiling points below -150 °F.  Examples are oxygen, nitrogen, and hydrogen.  A liquefied gas is defined as an element or compound that exists as a liquid at 70 °F under pressure ranging from 25 psig to

2500 psig.  Examples are chlorine, propane, and fluorocarbon refrigerants.

3.26  Pressure relief device (PRD).  The PRD is a pressure sensitive or a temperature sensitive mechanism that will protect the container against rupture by controlled release of the compressed gas.  Release may be due to pressure rupture of a rupture disk or by pressure activating a spring-loaded relief valve.  Release in the case of a fusible metal plug will be due to heat in the immediate environment greater than the melting point of the base metal (165 °F or

212 °F).  A combination device made up of a disk backed with fusible metal is designed to be used where container contents will not be released unless the necessary heat to activate the fusible metal and pressure in the burst range of the disk exist at the same time.  This provides better control over inadvertent loss of contents.  A combination PRD is never used on containers approved for charging 10 percent above marked service pressure (see 5.3.1.1.1).  Approved PRDs and applications are detailed in the CGA S-1.1.  A-A-59860 outlines PRDs in government applications as identified in table I.

TABLE I.  PRD designations.

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