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In a pressure test the piping system is subjected to an increased test pressure. The additional weight of the test fluid can create a separate static load case.
Before first start-up a piping system is subjected to a pressure above its maximum operating pressure. The test shows whether the fully installed system – pipes, welds, flanged joints – is strong and tight. It replaces neither the calculation nor weld examination; it concludes both.
The test pressure is set by the code. Under the Pressure Equipment Directive and EN 13480-5 the hydrostatic test pressure is the greater of two values: 1.25 times the maximum allowable pressure, scaled by the ratio of material strength at test and design temperature, or 1.43 times the maximum allowable pressure.
ASME B31.3 requires not less than 1.5 times the design pressure, likewise corrected by the ratio of allowable stresses. In both cases no component in the test section may be overloaded by the test pressure. Expansion joints, valves and instruments have limits of their own and are removed or isolated where necessary.
Testing is normally done with water. Water is practically incompressible; if a component fails, the pressure drops immediately. A gas under pressure stores many times more energy, which is released abruptly on failure. A pneumatic test is therefore considered only where water is not permitted or not practicable – and only with special safety precautions. ASME B31.3 specifies 1.1 times the design pressure for it.
For a gas or steam line, being full of water is the heaviest load of its life. Supports and structure have to carry this weight even if it occurs only once. The stress analysis therefore treats the pressure test as a separate load case: line cold, filled with water, at test pressure.
Variable and constant spring hangers remain locked; they are set for the operating weight, not the test weight. With unrestrained expansion joints the pressure thrust rises with the test pressure – the anchors have to withstand that too.
Most damage during pressure tests occurs at the edges of the test, not in the pipe.
What Entracon offers here is on the matching page.
See what we offer| Aspect | Hydrostatic test | Pneumatic test |
|---|---|---|
| Stored energy | Low | High – special safety precautions required |
| Additional weight | Full water filling, separate load case | Negligible |
| Follow-up work | Draining and drying | No drying |
| Normal case | Yes | Only where water is not permitted or not practicable |
For as long as the code requires as a minimum and as it takes to inspect all joints. The holding time depends on the code, the test procedure and the size of the system.
Not necessarily. What matters is whether the test pressure is permissible for the expansion joint and whether anchors and restraints carry the increased pressure thrust. Otherwise it is replaced by a spool piece or additionally secured.
After work on pressure-bearing parts, as a rule yes. The code and the responsible inspection body determine extent and type of test; for minor work, extended non-destructive examination may take the place of the pressure test.
One short conversation usually settles more than three quotations. Call or write — you will reach an engineer directly.
Start typing – for example “balancer”, “SAP” or “pipe stress”.
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