MIL-STD-1411B
shallow pitting, and sidewall rust stain are generally acceptable when diptube withdrawal is utilized.
c. When the commodity is a liquefied gas to be withdrawn as a liquid of high purity by inversion of the cylinder, the sidewalls, bottom, and shoulders shall be free of all contamination, rust, and corrosion to the reduced metal level. The cleaning procedure of choice is iron shot blast. Other mechanical or chemical methods may be used if residues from processing can be removed in accordance with ASTM D2200.
d. Special handling cylinders shall be immediately dried in accordance with 5.3.2.5.2 or
5.3.2.5.3 so the corrosion level will remain static until the cylinder is charged. Cylinders prepared in special handling must be charged immediately or they must be preserved with dry inert gas and closed by revalving or by plug and gasket.
5.3.6 External cylinder surface maintenance. The cylinder requiring external surface maintenance shall have the valve masked against stripping solutions and paint spray. The valve protection cap will be turned hand tight onto the cylinder flange. The cylinder must be cleared of decals and stickers, all old paint should be stripped, and the rust removed to the reduced metal. The cylinder shall be refinished in accordance with the requirements of CGA TB-17.
The materials supplied to paint government cylinders shall be in accordance with or equal to MPI Reference 9. Lacquer materials acceptable for painting government cylinders shall be in accordance with A-A-3165. Cylinders and valve protection caps shall be color coded and stenciled in accordance with MIL-STD-101. Paint shall be uniform in colors conforming to FED-STD-595.
5.3.6.1 Cylinder valve protection caps. Replace the cap on the cylinder flange. If the threads are not free running, clean both the cap and flange threads with a wire brush to remove rust or chase the threads with tap or dye as applicable. Cap threads that cannot be cleaned to run free shall be cause for rejection and replacement with a new cap in accordance with
MIL-DTL-17376/1. Cylinders under 625 cubic inches in water capacity are not required to have flanges and valve protection caps unless the cylinder is provided with a threaded flange.
5.3.6.2 Paint, decal, and rust removal. Before painting a government cylinder, the old paint, any decals, and oxidation shall be removed to the reduced metal in accordance with
TT-C-490. Decals and stickers must be removed before stripping, either by chemical or by mechanical systems. Chemical stripping systems using caustic or phosphate solutions perform well in removing paint, but do not attack the oxidized surfaces of denuded metal. This oxidation must
be removed by chemical reducing agents, mechanical abrasives, or a combination of both. Shot blasting is an effective means for removing hard paint without severe erosion of the metal cylinder wall in controlled processes. Removal of rust is achieved in a mechanical process of shot blasting and no need exists for rinsing residue or for drying as is the case with chemical processes.
5.3.6.2.1 Release of compressed gas in 150 °F stripping solution. DOT service pressure regulations are based on expansion limitations at 130 °F maximum. If cylinders containing compressed gas or liquefied gas residuals are subjected to temperatures in excess of 130 °F
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