Hydrostatic Test Pressure Calculator
Find the minimum test pressure for a piping system to ASME B31.3, for hydrostatic (water) and pneumatic tests.
- PT = 1.5 × P × ST/S = 1.5 × 20 × 1.163 = 34.88 bar(g)
- Pneumatic: 1.1 × P = 22 bar(g)
ASME B31.3 Test Pressure
Pneumatic: PT = 1.1 × P
ST is the allowable stress at test temperature and S at design temperature. When the design temperature is below the creep range and the stresses are equal, the hydrotest pressure is simply 1.5 × design.
Worked example
Design 20 bar(g) at a temperature where S = 118.6 MPa, tested cold where ST = 137.9 MPa: PT = 1.5 × 20 × 1.163 = 34.9 bar(g).
Frequently Asked Questions
What is the hydrotest pressure for piping?
Under ASME B31.3, at least 1.5 times design pressure, increased by the ratio of allowable stresses when the design temperature is higher than the test temperature.
Why remove instruments before a hydrotest?
Transmitters, gauges and control valves may have lower pressure ratings or be damaged by debris and water; isolate them or fit blanks.
How long is a hydrostatic test held?
ASME B31.3 requires at least 10 minutes, followed by an examination of all joints at the design pressure or higher.
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