Abstract: Pressure vessels are tested for structural integrity by recording acoustic events generated in the vessel's walls while it is immersed in water and subjected to internal pressure above the vessel's working pressure. Acoustic events are recorded by sensors fixed either to the wall of the vessel or to the walls of the water container in which the test is conducted. In preferred form, the vessel is water filled throughout the test and its volumetric increase with pressure is measured in an initial over-pressurization.