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

d. After the heating, all of the applicable portions of DOT regulation inspections, including retest, shall be performed.

5.3.2.5 Internal cylinder drying. Each cylinder that has accumulated water or has had water introduced for maintenance purposes shall be inverted and drained free of water and dried until the dew point of effluent gas is less than 40 °F when tested in accordance with

ASTM D2029 or by equivalent method. When preservation of the internal surfaces is required for periods of storage, for high purity conditions, or for aviator's breathing oxygen (ABO) cylinders, heat shall be applied to the cylinder or hot gas shall be passed through the cylinder until 180 °F surface temperature is reached. The cylinder shall be immediately valved closed or sealed with a plug and gasket. Medical gas cylinders shall be dried with the gas of intended use or with dry air.

5.3.2.5.1 Ambient air drying. This procedure is widely used in cylinder processing to achieve a dew point of 40 °F on the effluent side. Drying characteristics will vary widely with relative humidity and temperature. Controlled systems must be proven or constantly monitored by dew point testing or by equivalent analysis.

5.3.2.5.2 Hot nitrogen gas drying. Heated nitrogen is forced through a lance that is inserted to within one inch of the bottom of the cylinder. Hot nitrogen is passed through the cylinder until the external cylinder surface at the open end reaches 180 °F. The cylinder must be valved closed or plugged at this elevated temperature to ensure its dry interior condition.

5.3.2.5.3 Vacuum and heat drying. The cylinder is dried by a vacuum drawn on a cylinder immersed in a 180 °F water. A vacuum of not less than 3 inches of mercury absolute pressure must be maintained for 30 minutes. Without access to ambient air, the cylinder should be pressurized to not less than 5 psig with nitrogen gas or the gas of intended use and valved closed.

5.3.2.6 Valves and PRDs. Each cylinder valve requiring maintenance shall be repaired as applicable. Valves should be in accordance with A-A-59860 and may remain in service as long as they are functional, clean, and free of damage. PRD systems shall meet the requirements of 49 CFR 173.34 and shall be tested in accordance with CGA S-1.1. All materials used in fabrication as applied to government medical valves shall pass tests specified in

NASA-STD-6001.

5.3.2.6.1 Valve maintenance. Valves shall be cleaned free of insects, webs, dirt, paint, corrosion, oil, or grease. Valves may be effectively cleaned using a solvent in accordance with CGA G-4.1 or a commercial oxygen equipment cleaning solvent safe at ambient temperatures.

5.3.2.6.1.1 Hand wheels, packing glands, bonnet nuts, and valve seats. The use of salvaged hand wheels is acceptable whenever a match in drive can be made. Packing glands must be tightened to assure a gas-tight seal on the stem. Bonnet nuts must be locked tight. The valve seat must seal gas-tight when hand closed, and the stem must backseal when in the full open position. Damaged stems or plugs and integral seats shall be replaced with a manufacturer's kit.