What Is a Proof Pressure Test?

A proof pressure test is a non-destructive test in which a component such as a valve, hose, tube, cylinder or pressure vessel is pressurised to a specified level above its maximum operating pressure, held for a set time, and then checked for leakage or permanent deformation. If it holds pressure without leaking and returns to its original shape, it passes.

How a proof pressure test works

The component is connected to a test source, filled and vented, and pressurised in a controlled ramp to the proof pressure. It is then held for the specified time while pressure is monitored. Afterwards pressure is released and the item is inspected. The acceptance criteria are normally no leakage, no visible damage, and no permanent set beyond the allowed limit. Where deformation matters, expansion or dimensional change can be measured with instrumentation such as displacement sensors during and after the hold.

Proof pressure is normally set as a multiple of the maximum working or operating pressure. A factor of 1.5 times working pressure is common, but the factor and hold time are set by the applicable standard or customer specification, and some items use other factors.

Proof pressure, working pressure and burst pressure

Working (operating) pressure: the pressure the component is designed to see in normal service.
Proof pressure: a test level above working pressure that the component must withstand without permanent damage.
Burst pressure: the pressure at which the component fails. Burst testing is destructive; proof testing is not.

A proof test checks that a healthy part has the expected margin; it does not tell you the ultimate strength of the part.

Hydrostatic and pneumatic proof testing

Proof testing is usually done with a liquid (hydrostatic), typically water or oil, because liquid is nearly incompressible and stores far less energy than gas at the same pressure, so a failure releases much less energy. Pneumatic proof testing with gas is used where liquid is unsuitable, for example where a component cannot tolerate contamination or residual liquid, but it needs extra safety controls because the stored energy of compressed gas is much higher.

Proof pressure test equipment

Proof test rigs combine a pressure source (pump or intensifier), valves, calibrated pressure sensing, a protective enclosure and a controller that ramps, holds and records. The Neometrix hydraulic proof pressure test rig page describes a PLC-controlled hydrostatic system rated to 700 bar for validating valves, hoses and actuators. The 1000 bar hydraulic proof pressure test bench page describes a LabVIEW-controlled static proof pressure bench to 1000 bar, and the hydraulic pressure test bench page describes a SCADA-integrated hydrostatic and burst test system to 500 bar for tube assemblies. Machines at higher pressures are used for defence items: the bomb shell hydraulic pressure testing machine page describes proof-testing of empty shell bodies with an operating range to about 1400 bar and structural capacity to 1800 bar. For a conversion between bar and psi see the page on bar and psi pressure units.

Frequently asked questions

What is a proof pressure test?

It is a non-destructive test in which a component is pressurised above its maximum working pressure, held for a set time, and checked for leaks or permanent deformation.

What is the difference between proof pressure and burst pressure?

Proof pressure is a test level the component must survive without damage. Burst pressure is the pressure at which it actually fails, and burst testing destroys the part.

How much higher than working pressure is proof pressure?

A factor of 1.5 times working pressure is common, but the required factor and hold time are set by the applicable standard or customer specification.

Is proof pressure testing done with liquid or gas?

Usually liquid, because a liquid stores much less energy than gas at the same pressure and is therefore safer if a failure occurs. Gas proof tests need additional safety measures.