A hydrostatic pressure test fills a valve with water, raises the pressure and holds it to check for leaks. It proves the body does not leak or deform and that the valve seals when closed.
For many industrial valves the test follows API 598, which sets which tests to run, at what pressure, for how long and what leakage is allowed. European valves often follow EN 12266-1 instead.
The main tests under API 598
- The shell test pressurises the body and bonnet with the valve partly open. It runs at 1.5 times the valve's rated pressure at 38 °C, and no visible leakage is allowed.
- The backseat test checks the seal behind the stem on valves that have a backseat.
- The low-pressure closure test uses air or gas at low pressure to check the seat seals.
- The high-pressure closure test uses liquid at 1.1 times the rated pressure at 38 °C to check the seat.
Which tests apply to your valve
Which closure tests are required depends on the valve type, size and rating. The standard also sets minimum test durations by valve size, and allowed seat leakage rates for metal-seated valves. Soft-seated valves are normally expected to show no visible leakage.
How a good test is run
- The valve is clean, unpainted at the test areas and free of grease that could hide a leak.
- Water is clean and, for stainless steel valves, low in chlorides.
- Pressure gauges are calibrated, sized for the test pressure and have a valid label.
- Air is bled out before pressure is raised, so the reading is accurate.
- The pressure is held for the full time, and the inspector watches every joint.
- The valve is drained and dried after the test to prevent rust.
What the test report should show
Each valve, or each valve in a test batch, should have a record. It should list the serial or heat number, size, rating, test standard, test medium, pressures, durations and result. The tester should sign it, and the gauge certificate number should appear on it.
Ask for the record to link to the material certificates for the body and bonnet. If your project needs a witnessed test, a third-party inspector can sign as well.
Common problems
Weak plants sometimes shorten the hold time, test only a sample, or paint valves before testing. Some use gauges that are out of calibration. The safest check is to witness tests on a sample of valves, as described in inspections before machinery shipment.
For the wider design rules behind the test, read valve standards: API, ANSI and DIN.
Next step
We witness pressure tests, check gauge certificates and review test records before your valves are packed. Book a free sourcing review to plan the inspection.