Hydrostatic Test

The hydrostatic test, or hydrotest, is a cornerstone of safety in industries dealing with pressurized systems. The procedure involves completely filling the component with a liquid, ensuring all air is purged, and then using a pump to increase the pressure to the required test level, which is always significantly higher than the maximum allowable working pressure (MAWP). The pressure is held for a predetermined duration while the vessel is inspected for leaks or permanent changes in shape. The safety advantage of using a liquid like water is rooted in its low compressibility. If the vessel fails and ruptures, the pressurized liquid will only expand slightly, resulting in a rapid pressure drop and a simple leak. In contrast, a compressed gas (as in a pneumatic test) stores a vast amount of potential energy. A rupture during a pneumatic test would lead to a violent, explosive release of this energy, propelling shrapnel and creating a dangerous blast wave. The energy stored in compressed water is orders of magnitude less than that stored in air at the same pressure.

The test not only checks for leaks but also serves as a proof test for the vessel’s structural integrity. Any plastic deformation detected after the pressure is released (e.g., by measuring the volume of water displaced before and after the test) indicates that the material has yielded, and the component is rejected. This ensures that the vessel can withstand pressure spikes without failing.