Risks when testing with positive or negative pressure

When testing with positive or negative pressure, there is a significant risk of ill health and accidents for those carrying out the test, and for those in or near the place where the test is carried out.

As an employer, you therefore need to ensure that testing with positive or negative pressure always takes place safely.

Risks when testing with positive pressure

The main risks associated with testing with positive pressure are the rupture, fragmentation or breakage of the test equipment or the device under test. This can happen even at low pressure.

Risks when testing with negative pressure

The main risk when testing with negative pressure is that the device under test implodes, i.e. collapses inwards Splinters may then occur which could injure people nearby.

Test with liquid in the first instance

Pressure testing should always be performed with liquid in the first instance. The risks of using gas in positive pressure testing are much greater than if you use liquid. The energy content at the same pressure and volume is 200 times greater if you pressurise with gas, which makes the explosive effect much greater.

When performing pressure testing with liquid, you must ensure that the object to be tested is completely filled with liquid. If there are air spaces in the object, the consequences of a possible leak or crack increase significantly.

Pressurising with gas

When performing pressurisation with gas, you may need to be accredited by Swedac (the Swedish Board for Accreditation and Conformity Assessment). If you carry out gas pressurisation without being accredited, you may be ordered to pay a sanction fee.

There are four exceptions to the accreditation requirement when performing gas pressurisation. The exceptions are

• if the control pressure is 0.03 bar or lower
• if the control pressure is a maximum of 3 bar and the volume of the object to be tested multiplied by the pressure to be used is a maximum of 30 bar litres
• when setting the opening pressure of the safety equipment, if the equipment has previously undergone a pressure test
• if the test is carried out in a specially designed protective device.

Assess the risks of the work before testing

Before testing, you as an employer must conduct a risk assessment of the work. The risk assessment should show what safety measures and safe distances are needed before work starts. How big the risk area around the test object is depends on the pressure wave that can occur and how far you calculate that parts of the device can be thrown if the device breaks.