Hydrostatic Pressure Testing is a nondestructive testing (NDT) method of finding leaks or verifying performance and durability in pressure vessels such as pipe, tubing, and coils. Although this is considered nondestructive testing and failures are rare, they can occur when the test piece does not meet performance or durability specifications and may render the piece unusable.
Hydrostatic Pressure Testing usually entails filling the pipe, tubing, or coil with liquid, bleeding out air, pressurizing the piece, and then examining it for leaks or permanent changes in shape. A nearly incompressible (compressible only by weight, not air pressure) liquid, usually water or oil, is used to fill the test piece because it will only expand by a very small amount if the piece fails, and therefore, minimizes the chance of injury or further damage. Hydrostatic pressure testing also can be performed with pressurized air, but is generally completed with the vessel under water for safety reasons. Although a testing laboratory may be equipped to perform hydrostatic pressure testing with water, oil, or air under water, water is the most commonly used test medium because it is less expensive than oil and easier to set up than air under water.
This nondestructive testing method is used to test tubing, pipe and coils to pressures measured in PSI (e.g. to 10,000 PSI). The amount of pressure used in hydrostatic pressure testing is always considerably more than the operating pressure, or the pressure the vessel will be subjected to in the course of operation, to give the customer a margin for safety. Typically the test is performed at 150 percent of the design or working pressure. For example, if a pipe was rated to a working pressure of 2000 PSI, it would be tested at 3000 PSI.