Washington Hydraulic Overpressure Test (WHO) is a non-destructive testing method used in the oil and gas industry to test the integrity of pressure vessels such as tanks and pipelines. During the test, the vessel is filled with pressurized water and gradually increased until it reaches a predetermined test pressure. This pressure is held for a specified period of time to ensure the vessel is able to withstand the pressure without leaking. The test also serves to check the structural integrity of the vessel and its components. There are two main types of WHO: the static test and the dynamic test. The static test involves filling the vessel with water and then applying a constant pressure for a predetermined amount of time. The dynamic test involves gradually increasing the pressure in the vessel until it reaches the test pressure, and then maintaining that pressure for a period of time.