Preparing a pipeline pressure test properly: checklist for site and project managers
The pressure test is the moment that shows whether welds, flanged joints and supports hold. It comes at the end of installation and is therefore almost always on the critical path – every repeat costs days. This checklist shows what must be done before, during and after the pressure test, and where blinds and flanged joints typically cause delays.
Checklist: before the pressure test
Every item should be ticked off before filling starts. Most repeat tests are caused not by leaking welds but by forgotten preparations.
- ☐All welds completed, heat treatment finished
- ☐Non-destructive testing passed and documented
- ☐Welds accessible for visual inspection – not yet insulated or coated
- ☐Line clean inside, foreign objects removed
- ☐All final supports installed and load-bearing
- ☐Spring hangers locked where filling would overload them
- ☐Buried lines largely backfilled, only the test points left exposed
- ☐Test section defined, blinds inserted according to the blind list
- ☐Blinds rated for the test pressure
- ☐Valves, pumps, equipment and instruments removed or safely isolated
- ☐Expansion joints secured against overextension
- ☐Calibrated pressure gauges at the start and end of the test section
- ☐Fill connection at the lowest point, vent at the highest point
- ☐Test medium defined – for stainless steel, water with low chloride content as specified by the project
- ☐Test area cordoned off, responsible persons and witness (operator, inspection body) informed
Sequence of a hydrostatic test
- 1Fill from the lowest point. Fill slowly and vent completely at the highest point – trapped air distorts the pressure reading and makes the test more dangerous.
- 2Raise the pressure in stages. Go up to the test pressure in stages and check for leaks in between.
- 3Hold the test pressure. Hold for the time required by the code or specification; read and record the pressure at both gauges.
- 4Visual inspection. Examine welds and flanged joints for leaks at reduced test pressure or design pressure.
- 5Depressurise and drain. Release the pressure in a controlled manner, vent the line so that no vacuum forms, and drain it completely – for stainless steel and where there is a risk of frost, dry it as well.
- 6Test record. Record test pressure, holding time, temperature, gauges and witnesses, and have the record signed.
Test pressure at a glance
The level of the test pressure depends on the code. In simplified terms, the following applies to the hydrostatic test:
| Code | Hydrostatic test | Pneumatic (air or gas) test | Note |
|---|---|---|---|
| EN 13480-5 | the greater of 1.25 × PS (with temperature correction) and 1.43 × PS | only in justified cases, with additional safety measures | PS = maximum allowable pressure |
| ASME B31.3 | at least 1.5 × design pressure (with correction for the design temperature) | 1.1 × design pressure | holding time at least 10 minutes |
Simplified presentation, without guarantee. The applicable edition of the code, the pipe class and the project’s test procedure are authoritative. The test pressure must not overload any component – valves and blinds have their own limits.
Water or air?
The hydrostatic test is the standard case. Water is almost incompressible: if a weld fails, the pressure drops immediately without releasing much energy.
Compressed air or nitrogen, by contrast, store many times more energy. If a component fails, it can throw parts away with great force. A pneumatic test is therefore only an option when water is ruled out – for example for lines that cannot tolerate water or cannot carry its weight. It requires a larger safety distance, a separate risk assessment and usually a lower test pressure.
Blinds and flanged joints: the typical delay
For every pressure test, flanged joints are opened, blinds inserted and removed again after the test. With many test sections, this quickly adds up to hundreds of joints. If a blind is missing from the list or a joint is not closed correctly again, this only shows up during commissioning.
A proven approach is a blind list with the number, location, size, pressure rating and status of each blind, clearly tagged blinds on the line, and closing every joint with a new gasket and a tightening record.
We open and close flanged joints in a controlled manner – by torque or bolt tensioning, with calculated bolt preload and a record for each joint. This means blinds are inserted and removed quickly, and the joints are documented as leak-tight after the test.
After the pressure test
- ▸Remove blinds: according to the blind list, ticking off each position.
- ▸Close joints: with new gaskets and documented bolt preload.
- ▸Flush and dry: depending on medium and material; for stainless steel, do not leave standing water behind.
- ▸Insulation and coating: on the welds only now.
- ▸Spring hangers: unlock before the line goes into operation.
Frequently asked questions
Why must all supports be installed before the pressure test?
A water-filled line weighs many times more than an empty one. Without the final supports, the weight hangs on welds and on the connections of pumps and equipment. This can deform components and distort the result.
May valves be included in the test?
Only if they are rated for the test pressure and the specification permits it. Isolation valves are usually tested in the open position; control and safety valves, instruments and expansion joints are removed or isolated by blinds.
Which blind do I need for the pressure test?
One that is rated for the test pressure and the nominal size – thin blinds intended only for isolation without pressure are not sufficient. The thickness follows from test pressure, nominal size and material; many projects specify it in the pipe class or in a separate table.
What if a flanged joint leaks during the test?
Release the pressure, establish the cause and re-bolt the joint – do not re-tighten under test pressure. Common causes are uneven bolt preload, a damaged flange face or the wrong gasket. Damaged flange faces can be remachined on site.
General description based on practical experience, without guarantee. The code, pipe class, test procedure and operator requirements are authoritative.
Flanged joints for the pressure test – fast and documented
Send us your blind list or test sections – we will plan personnel and tools for inserting and removing the blinds.