MIL-STD-1411B
5.3.2.4 Internal cylinder surface cleaning. Cylinders that require cleaning of the internal surface of contamination, rust and corrosion, or removal of a degraded lining material shall be processed, as applicable, to restore the cylinder for use to contain the gas specified in the contract or work order.
5.3.2.4.1 Aqueous solution detergent washing. Cylinders can be cleaned by use of aqueous detergent solutions to remove most water and oil based contaminants. All detergent residue must be removed by rinsing and the cylinder must be dried to a dew point less than 40 °F (see 5.3.2.5). Detergent solutions are frequently used to remove organic materials from cylinder interiors. Most effective cleaners are alkaline-based solutions of potassium or sodium hydroxide, about 8 percent Baume concentration. Solutions are used hot and can cause severe irritation on skin contact, or extensive damage if contact is made with the eyes or mucous membranes. Protective clothing shall be worn to protect personnel from the caustic activity of these solutions. Alkaline or detergent solutions do not dissolve oil, grease, or other organic contaminants, but they function by emulsifying them. The cleaning agents attack films of oil or grease, and break them into globules or particles. Each particle of insoluble liquid or solid material is surrounded by a film of closely adhering detergent, and allows it to float free in the liquid. Heat and agitation enhance cleaning action and thorough rinsing washes the free particles away with the wastewater. Clean hot water must be used to prepare an effective cleaning solution. Exceptionally hard water will form insoluble precipitates with the mineral salts in the water and when used will require filtration to prevent clogging of sprayer heads and nozzles. The strength of the solution should be no greater than required for effective cleaning.
5.3.2.4.1.1 Procedure.
a. Cleaning the outside of a cylinder: If inspection shows that oil or grease is confined to the exterior surface of a cylinder below the neck ring skirt and none is on the neck ring or valve, remove all external oil by washing with the alkali solution. A stiff brush or rag may be used on the parts difficult to clean. After all contamination is removed, rinse the cylinder thoroughly
with clean running warm water and return it to service.
b. Cleaning the inside of a cylinder: Never use the same alkali solution or container for internal washing that has previously been used for external washing. Prepare a fresh batch and proceed as follows:
(1) Fill the cylinder to a little over half its capacity with a solution of hot alkali, and plug the end of the cylinder with a flanged plug and a gasket.
(2) Lay the cylinder on the floor and roll it back and forth for about 15 minutes. If a cylinder roller is available, adjust it so the cylinder is horizontal and allow the cylinder to rotate for 15 minutes.
(3) Immediately upon completion of the rolling, stand the cylinder up, remove the plug, and completely fill the cylinder with clean tap water. Be sure the cylinder is full, as the interior walls must be kept wet until the cylinder is rinsed.
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