After all the forming, welding, and non‑destructive testing, the vessel faces one last ordeal: the hydrostatic pressure test. It is simple in concept – fill it with water, pressurize it to a value above the design pressure, and watch for leaks or permanent bulging. But under PED, the test has specific rules.
First, the test pressure must be at least 1.43 times the maximum allowable pressure for most vessels. Second, the water temperature must be kept above the material’s nil‑ductility transition temperature – a cold vessel is a brittle vessel. Third, the pressure gauge used must be calibrated and traceable to a national standard. Fourth, the test must be witnessed by someone independent of production for category III and IV vessels – often a Notified Body inspector.
During the hold period, typically 30 minutes, inspectors check every weld, every nozzle, every threaded port with mirrors and flashlights. A single drop of water seeping out means failure. After depressurization, the vessel is measured again to ensure no permanent growth. Only when the hydrotest is signed off does the manufacturer attach the CE marking and issue the Declaration of Conformity. That final squeeze is not just a test – it is the vessel‘s birth certificate.
Post time: May-27-2026