Refrigeration pressure test: strength and tightness test, step by step
Step-by-step pressure test for refrigerating systems: test pressure 1.1 or 1.43 × PS, nitrogen, danger zone, tightness test, safety and what goes in the test certificate.
Key points
- A new or modified refrigerating system must be strength tested and tightness tested before it is charged with refrigerant [1].
- Pipework is tested at at least 1.1 × PS when the system is in category I under the Pressure Equipment Directive, and at at least 1.43 × PS in higher categories [1][2].
- Use dry nitrogen, never oxygen or compressed air with oil, and make sure the pressure cannot rise above the intended value [1].
- A gas test stores a lot of energy. Close off the danger zone and keep away while the pressure is high.
- Document the test in a certificate: test pressure, duration, medium, result and who carried it out.
Why two tests?
The strength test shows that pipes, joints and components withstand the pressure with a good margin. The tightness test shows that the system does not leak. EN 378-2 requires both for systems assembled on site, and for the parts that have been changed during a modification [1]. Components such as compressors and pressure vessels have normally already been tested by the manufacturer. On site, the pipework and the joints between them are then tested.
Which test pressure?
The test pressure is based on the maximum allowable pressure (PS) of the system part, which is on the nameplate and in the documentation. PS differs between the high and low pressure sides and depends on the refrigerant and the ambient temperature the system is designed for [1].
| Case | Minimum strength test pressure |
|---|---|
| Pipework in a system in PED category I, or under sound engineering practice (Article 4.3) | 1.1 × PS |
| Pipework in a system in category II or higher | 1.43 × PS |
The category is determined under the Pressure Equipment Directive 2014/68/EU from PS, pipe size or volume and the fluid group of the refrigerant [2]. Check the manufacturer's instructions for components that cannot withstand the test pressure, for example some valves, sensors and pressure switches. They are disconnected or isolated during the test.
Step by step
- Plan the test: decide PS, test pressure and test medium, which parts are included and how they are separated from the rest of the system. Carry out a risk assessment.
- Disconnect or isolate components that cannot withstand the test pressure. Safety valves are normally removed and the connection plugged, or isolated so that they do not open during the test.
- Connect the nitrogen cylinder via a pressure regulator with a gauge and a safety valve or pressure limiter after the regulator, set just above the test pressure. This prevents the pressure from rising above the intended value.
- Close off and mark the danger zone around the pipes. No one may be in it while the pressure is raised or held at test level.
- Raise the pressure in steps, for example to half the test pressure and then in steps of one tenth, and wait a while at each step.
- Hold the test pressure for the required time. Read the gauge and check that the pressure does not fall. No one may work on the pipes while the pressure is high.
- Lower the pressure to the tightness test level, which must be no higher than PS. Carry out the tightness test: search for leaks at all joints with leak detection fluid or a suitable leak detector.
- If a leak is found: release all the pressure before you repair. Pressure test and tightness test again after the repair.
- Release the nitrogen safely, refit the safety valves and components that were disconnected, and continue with evacuation.
Test medium
Use dry, oxygen-free nitrogen. Oxygen must never be used, because it can ignite oil and cause an explosion. Compressed air contains moisture and often oil and should not be used in refrigerating systems. EN 378-2 also allows a hydrostatic test with liquid, but it is rarely used in refrigerating systems because the liquid is hard to remove [1].
Safety
A test with gas stores much more energy than a test with liquid at the same pressure. If a joint or pipe fails, parts can be thrown with great force. Keep the danger zone closed off, wear safety glasses, and never tighten fittings or knock on pipes while the system is pressurised.
Test certificate
After the test, a certificate must be written and kept with the plant documentation. It should show:
- The plant, the system part and which pipes and components were tested.
- PS and test pressure for the strength test, test medium and how long the pressure was held.
- Pressure and method for the tightness test.
- Result: passed, or which leaks were found and repaired.
- Date, name, company and signature.