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

TABLE I.  PRD designations - Continued.

1   The use of PRDs is prohibited in certain gas service applications by 49 CFR 173.301.

2   A spring loaded, reseating PRD (CG-7) is also known as a pressure relief valve (PRV).

3.27  Product item description (PID).  When a government agency procures a commodity, it must first be identified by a PID and be included as an approved Federal Item Identification arranged in narrative or tabular form determined appropriate.  The PID includes specification

and other reference numbers, when applicable.  Unless specification numbers are qualified by a suffix or note, the item complies with the latest revision or amendment.

3.28  Registered facility.  49 CFR requires that each hydrostatic test facility be registered with the DOT before it is placed in operation testing cylinders.  This registration is a control on the installed equipment for safety and accuracy.  Facilities performing UE must also be registered with the DOT and receive a special permit before they are placed in operation testing cylinders.

3.29  Spun cylinders.  Spun cylinders are fabricated from seamless tube stock of a diameter and wall thickness of the specified cylinder.  A predetermined length is placed in a lathe and spun,  and both ends are closed by heating and shaping.  In shaping, the side wall is flowed inward until all the slag and edge stock are brought to the center of the cylinder top and bottom.  The top shoulder is shaped and handled much like a drawn cylinder.  It is drilled and tapped for proper valve inlet threads.  The bottom is bumped back for standing stability and the center is broached free of slag and oxides.  In a controlled atmosphere, the metal is again flowed inward and closure is completed by inert welding.  If a failure in closure occurs, the bottom, which is heavier than the side walls due to inward flow of steel, will be drilled, tapped, and plugged to effect an acceptable closure in accordance with 49 CFR.  Spun cylinders are in general use in the government system in DOT 3A and DOT 3AA applications.

3.30  Tare weight (TW).  Tare weight is used to determine the quantity of gas commodity required to charge a cylinder by weight.  The tare weight of a compressed gas cylinder includes the empty cylinder with its valve, but does not include the valve protection cap.  Tare weight is generally marked in pounds and tenths of pounds, following the letters "TW", for liquefied gas applications.  The tare weight of cylinders in acetylene service is required to be permanently marked on the cylinder, flange, or cylinder collar.  The tare weight of cylinders in acetylene service includes the acetone and filler material.  Tare weight markings on acetylene cylinders are generally indicated by a whole number for pounds and a whole number in 4-ounce increments.

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