Gate valve hydrostatic testing: shell strength and seat leakage tests
Every gate valve is pressure-tested before shipment. Buyers should know what was tested, at what pressure and to which standard, because that defines what the certificate actually says.
TAZ Engineering Team · · 7 min
Shell test
The valve is filled with water in the partly open position and pressurised above its rating. Under common standards such as API 598 and EN 12266-1 the shell test pressure is about 1.5 times the rated pressure at ambient temperature. The test checks for leakage through the body and bonnet walls and the body-bonnet joint. Hold time depends on DN and standard.
Seat test
The valve is closed and pressurised from one side, then the other. A liquid seat test is usually at about 1.1 times the rated pressure. Leakage past the closure is measured and compared with the specified rate. A low-pressure air seat test may be added.
Leakage rates
EN 12266-1 and GOST 9544 use letter classes. Rate A means no visible leakage during the test and is typical for resilient seats and many metal seats. Rates B, C, D and beyond allow defined leakage depending on DN. API 598 sets its own allowable values for each closure type. Always state the leakage rate and standard in the order; "zero leakage" alone is interpreted in different ways.
Backseat and packing
Valves with a stem backseat have it tested for tightness, and the packing is checked during the shell test.
What to receive
A test report with serial number, date, standard, pressures, hold times, test medium and result, signed by quality control and, for export orders, in English. Tests can be witnessed by the buyer or a third-party inspector. TAZ tests every gate valve on its own bench and states the test standard in the technical offer.
Checklist
- test standard
- shell test pressure
- seat test pressure
- leakage rate
- test medium
- hold time
- backseat test
- serialised report
- witness inspection