Hydrostatic testing is the standard method of testing cylinders in the compressed gas industry. It is a nondestructive test procedure used to identify leaks, structural flaws, durability, and corrosion. Cylinders must be subjected to a thorough periodic inspection and requalification process. During periodic requalification, each cylinder must be examined internally and externally for damage and degradation then subjected to a hydrostatic pressure test to the design test pressure.

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 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.

GA Cylinder and Hydrotest personnel have been professionally trained to perform cylinder re-qualification based on DOT regulations, Compressed Gas Association (CGA) guidelines and stringent internal procedures.

Testing consists of enclosing a cylinder filled with water inside a test jacket filled with water. Pressure is then applied internally to the cylinder, causing the cylinder to expand. The total and permanent volumetric expansions of the cylinder are determined by measuring the amount of water displaced by the expansion of the cylinder when under pressure and after the pressure has been released.

A hot-air dryer is used to ensure all cylinders are properly dried after testing, reducing the risk of internal corrosion and is a requirement for operating an approved facility. External and internal visual inspections of cylinders are performed. Only after completing these procedures satisfactorily may a cylinder return to service.