MIL-STD-1411B
from the total expansion to calculate the elastic expansion. An acceptable cylinder will have a permanent expansion less than ten percent of its total expansion. A proper hydrostatic test is the basis for a valid estimate of the average wall thickness of the cylinder, and therefore a measure of the erosion of the walls in corrosion processes. Hydrostatic pressure test procedures are defined under 49 CFR. Additional details for hydrostatic test procedures are presented in
CGA C-1.
3.20 Liquefied petroleum gas (LPG). LPG is a term defining certain combinations of hydrocarbon gases such as butane, propane, isobutane, and butane-propane as mixtures. These compounds, under their own contained vapor pressure, will maintain a liquid state at the temperature of 70 °F. LPGs are compounds with molecules containing three or four carbon chains and are the fraction of petroleum separation falling between the natural gases and the gasolines. Natural gas is made up of methane and ethane, one- and two-carbon chain molecules, which have high pressure properties. Longer chain molecules including the N-pentanes are removed with the gasolines. LPGs have specific gravities ranging from 0.300 to 0.630, with better than 95 percent falling between 0.508 and 0.584. Propane has a boiling point of -44 °F. Liquefied propane in a container at 70 °F will maintain a pressure head of approximately
100 psig.
3.21 Medical gases. Gases used by the government medical services for medical purposes are oxygen, nitrous oxide, and ethylene oxide-dichlorodifluoromethane mixture (sterilant). Whenever appropriate in this standard, the term "medical gas" should alert the contractor to certain necessary precautions, particularly concerning materials employed in oxygen valves.
3.22 Nonshatterability identification. Nonshatterability is the property of the metal in a cylinder that causes it to remain in one piece rather than to fragment when a cylinder bursts from excessive pressure or when pierced by a high velocity projectile. Nonshatterable cylinders will be identified by one of the following markings stamped into the metal of the cylinder: "NONSHATTERABLE", "NONSHAT", or "SHATTERPROOF". DOT 3AA cylinders 4 inches or larger in diameter are accepted as nonshatterable, and all cylinders manufactured after June
1944 stamped 51-C-31 (INT) or 51-C-31 are accepted as nonshatterable. Cylinders identified as SPS 844 (INT), SPS 1022 (INT), 51-C-26 (INT), 51-C-41 (INT), 51-C-26, and 51-C-27 should be considered nonshatterable. Other cylinders have been determined to be nonshatterable through testing procedures and are so marked (see 5.1.1.5).
3.23 Office of Hazardous Materials Safety. Important assignments for the compressed gas industry are the approval of cylinder repair, rebuild, remanufacture, and testing facilities, the approval of hydrostatic test and UE facilities for cylinder testing, the approval of pressure relief device (PRD) designs for pressure vessels, and the control of cylinder identification markings. These responsibilities are assigned to the Associate Administrator for Hazardous Materials Safety, Office of Hazardous Materials Safety, U.S. Department of Transportation under
49 CFR 173.300a and 49 CFR 173.34.
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