Tanks containing gas under pressure must be tested every five years.
Title 49 of the Federal Regulations covering the transportation of compressed gas tanks administered by the Department of Transportation states that all tanks that contain compressed gases must be hydrostatically tested for structural integrity. The tanks, made of steel or aluminum, can develop cracks or a loss of tensile strength. Hydrostatic testing identifies tanks that no longer have the required margin of safety.
Requirements Under the Law
The requirements for hydrostatic testing are covered under section 180.407 of the regulations. They state that the tank to be tested must be filled with water and pressurized to 167 percent of the maximum pressure listed on the side of the tank. The tank, including all of the valves and other closures, must hold the test pressure for at least 10 minutes without leaking or bulging.
There is a further test for smaller tanks, such as those used in scuba diving. The tester fills the tank with water and submerges it in another tank, also filled with water. He pressurizes the tank to 167 percent of the maximum pressure and the tank expands permanently.
The tester measures the amount of permanent expansion by measuring the amount of water displaced in the larger tank. If the tank expands more than 10 percent, the tank is rejected.
Requirements for Testing and the Tester
Testing must be done by a licensed tester with standard equipment designed for the task. The tank has to be tested every five years with a six-month grace period.
The tank has to be tested more often than every five years if there are any visual signs of degradation or damage or if the tank has not been used for a year.