29 Hydrostatic Testing (Hydro)

Hydrostatic testing (hydro) uses water, air, and oil to test welds such as pressure vessels or pipe lines. the test is not difficult, although it requires some training, and can be low cost to perform. Hydrostatic testing is often used for proof testing, to demonstrate the ability of the welded structure to carry loads equal to or in excess of the anticipated service conditions. Hydrostatic testing must be used with care to prevent a catastrophic failure caused by release of stored energy, and there must be adequate venting to prevent the tested item from collapse (sucking in) when it is drained.

When performing hydrostatic testing on an atmospheric pressure storage tank, the the container is tested for its ability to withstand a certain level of pressure. For components built to the ASME Boiler and Pressure Vessel Code, this pressure is 150% of design pressure. For other components, the test pressure may be based upon a fixed percentage of the minimum yield strength. After a fixed holding time, the container is inspected for soundness by visually checking for leakage, or by monitoring the hydrostatic test pressure for any drop.