British Standards, EN378 Pressure Testing
24th January 2025
Technical Insight
Denis McCrohan – Beng Mech Eng(Hons), M.inst.R – Senior Technical Consultant
Historically, within the refrigeration industry new assemblies have been verified as leak tight through the pressure decay method. This method involves pressurising the complete new assembly with nitrogen to 95% of the maximum working pressure (MWP) and holding it for a set time. The minimum time would normally be 24hours and a connected gauge allowed continuous monitoring of the held pressure. Whilst previously deemed an acceptable standard method it is open to several factors that can affect its accuracy:
- Pressure gauge scale.
- Ambient temperature change.
- Inability to indicate very small leaks.
It is in the best interest of all parties to ensure there are no leaks on a completed assembly before the process of vacuuming and charging with refrigerant.
EN378 Refrigerating systems and heat pumps – Safety and environmental requirements, was updated in 2016 and yet we still encounter refrigeration system installations tested using the no longer suitable pressure decay method which does not comply with the tightness testing requirements of BS EN378-2 and the demonstration of leak tightness to a maximum 3g of refrigerant per year at 0.25 x PS.
To help illuminate this, our Senior Technical Consultant, Denis McCrohan, has created a basic overview explaining what the industry approved method is and why we should follow it.
General
The pressure testing requirements for refrigeration systems can be found in BS EN 378-2 and are mainly covered in clauses 5 and 6.
• Clause 5 covers the testing of components.
• Clause 6 covers the testing of assemblies.
In the main, an assembly is classed as the finished, site installed refrigeration system, consisting of separate components connected by pipework. All the separate components have in themselves been already tested, leaving only the interconnecting pipework of the final assembly to be tested.
Before any refrigeration installation is permitted to be put into service it must first undergo a series of pressure testing. This testing includes the following.
• A strength test.
• A tightness test.
Pipe Work Category
The pressure equipment category of the final assembly’s pipework will fall into one of two groups.
• Sound Engineering Practice (SEP) and Category 1. The pipework in this group must be installed by engineers with certification showing they have been assessed in accordance with the brazing requirements laid out by the BRA/IoR.
• Categories 2, 3 and 4. The pipework in this group must be installed by engineers with the certification showing they have been assessed in accordance with the brazing/welding requirements laid out by a Notified Body.
Note: a system’s pipe network can be made up of different sections of SEP/Category 1 and Category 2 pipework and tested separately as such.
Strength Testing (Site Installed Assemblies)
Before a strength test of the final assembly can by performed, its maximum allowable pressure (PS) must be known. The system will then be strength tested to a factor above this PS value.
For SEP/Category 1 pipework:
Test the piping and its joints at a minimum of 1.1 x PS.
For Category 2 and higher:
Test the piping and its joints at a minimum of 1.43 x PS.
OR
Test the piping and its joints as described in EN 14276-2.
OR
Test the piping and its joints at a minimum of 1.1 x PS, and in addition, 10% of the permanent joints shall be submitted to non-destructive testing in accordance with EN 12799 for brazed joints and EN ISO 10675 Parts 1 and 2 for welded joints.
Strength pressure tests should be carried out using Dry Nitrogen (some gas suppliers may call Dry Nitrogen by another name, Oxygen Free Nitrogen. They are mistaken, I’ve always known Nitrogen to be Oxygen free).
Tightness Test (General Requirements)
Tightness testing must be performed before the permanent joints are covered up with pipe insulation, paint or any other substance that will prevent access to the joints being leak tested. The “Pressure Decay” method for tightness testing the system is NOT permitted as it does not meet the “Tightness Test Acceptance Criteria”
Tightness Test Acceptance Criteria
For systems being charged with refrigerants having a GWP > 150 the pass threshold is no leak shall be detected using equipment with a capability of 10-6 Pa.m3/s (10 µW) or better. This can be achieved using a helium or hydrogen electronic sniffer.
For systems being charged with refrigerants having a GWP < 150 the pass threshold is no leak shall be detected using equipment with a capability of 10-3 Pa.m3/s (10 mW) or better. This can be achieved using water with a foaming agent.
Refer to EN 1779 for a list of alternative leak test methods.
Systems shall be pressurised using a non-hazardous substance such as Dry Nitrogen when testing using water with a foaming agent or one employing a trace gas, such as helium or hydrogen, when testing with a handheld electronic leak detector.
Tightness Test
With the system pressurised, ALL joints shall be tested using equipment capable of detecting leaks to the acceptance criteria listed above.
Conclusion
The tightness testing criteria threshold has been made more stringent specifically to further reduce the unintentional release of environmentally damaging refrigerants. The added benefit to the end user is the avoidance of increased energy consumption of systems running at a low charge, increased maintenance cost to replace lost refrigerant and down time associated with finding and repairing leaks in an installed system.
Following EN 378 Tightness Testing Criteria helps ensure:
- Legislation compliance
- Reduced scope 1 emissions from refrigerant loss
- No increase in running cost through low charge
- Minimised downtime
- Reduced maintenance cost
If you would like to know more about tightness testing, F-Gas legislation compliance or if you have any questions, get in touch.
