By Bruce J. Cavallari

Hydrostatic testing is the standard method of testing cylinders in the compressed gas industry. The water jacket method of testing cylinders consists essentially of enclosing the cylinder, suspended in a jacket vessel, and measuring the volume of water forced from the jacket on application of pressure to the interior of the cylinder. The pressure applied is five-thirds the operating pressure unless otherwise specified by the manufacturer. Therefore, a 4,500-pound-per-square-inch (psi) cylinder would be tested at 7,500 pounds psi. This method is used to determine the elastic expansion, which is directly related to the cylinder`s average wall thickness.

 Department of Transportation (DOT) regulations require that each cylinder be inspected periodically internally and externally, calibrated testing equipment and test gauges be used, and every cylinder used for the storage of compressed gases such as air or oxygen be retested. The exact laws are in the Code of Federal Regulations (CFR), Part 49, subpart 173.34(e). The DOT requires each testing facility to submit to regular inspections; and each facility must maintain records of all tests performed, all persons performing the tests, and regular training records of personnel. The DOT was established in 1967 and assumed the responsibility for the safety regulations formerly administered by the Interstate Commerce Commission.