Installation
Strength and tightness test pressures (BS EN 378-2)
- where
- minimum strength test pressure (bar g)
- maximum allowable pressure of the side under test (bar g)
- strength test pressure for Category II and above (bar g)
- tightness test pressure (bar g)
Explain this equation
Gives the strength and tightness test pressures for refrigerating system pipework from its maximum allowable pressure, PS. Use it when planning a nitrogen pressure test.
PS is the highest pressure that side of the system is designed for, usually on the nameplate or in the design. The strength test proves the pipework will not fail, so it goes above PS: at least 1.1 times, or 1.43 times for higher category assemblies. The tightness test looks for leaks and is done at no more than PS.
Fixed multipliers set by the standard, giving a safety margin over the design pressure.
Sense check: an R410A high side with PS = 26.1 bar g would be strength tested at about 28.7 bar g, or 37.3 bar g at 1.43 × PS, and leak tested at up to 26.1 bar g.
Watch out: never test above the rating of any component left in circuit. Isolate or remove parts not rated for the strength test, and use oxygen-free nitrogen through a proper regulator.
Gives the strength and tightness test pressures for site-assembled refrigerant pipework from the maximum allowable pressure (PS) on the equipment label.
Enter your values to see the result.
Good to know
On site the minimum strength test of 1.1 × PS is normal for SEP and Category I pipework; Category II and above needs at least 1.43 × PS (or 1.1 × PS with 10% NDT of permanent joints). Never exceed the PS or test pressure of any component, so isolate or remove compressors, controls and relief valves that are not rated for it. Use oxygen-free nitrogen, raise pressure in steps of no more than 3 bar, and keep people clear during the strength test. High and low sides usually have different PS values.
Common mistake
Testing the whole system to the high-side figure with the low side open, or testing above a component’s rating because the pipework can take it.
Limits
Summary of the EN 378-2 test factors as given in UK trade guidance; the standard and the equipment manufacturer’s instructions take precedence. Gauge pressures.
Sources
- Cool Concerns CS 21: PS – maximum allowable pressure (EN 378-2: strength test minimum 1.1 × PS, maximum 1.43 × PS; tightness test 1.0 × PS; R407F example)
- Wave Refrigeration: British Standards, EN 378 pressure testing (Category I pipework 1.1 × PS; Category II and above 1.43 × PS or 1.1 × PS with 10% NDT)
- Institute of Refrigeration, Service Engineers’ Section: Good practice guide – leak tightness testing (OFN, pressurise in steps of no more than 3 bar, never exceed PS)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the equipment manufacturer’s data, CIBSE guidance, BS EN 378, the F-gas Regulations and your company procedures. Refrigerant work needs the correct F-gas certification.