Helium leak testing is used to test for leaks on a multi piece assembly that is welded together or sealed using elastomer seals or metal to metal seals.
Testing is configured in one of two methods:
The internal cavity of the assembly is evacuated via a running vacuum pump. A helium leak detector (Mass Spectrometer Leak Detector) is connected to the common evacuated space and helium gas is sprayed upon the test specimen's sealing connections. If there is a leak within the seal, helium will enter through the leak and be detected by the Helium Leak Detector connected to the common evacuated space.
The internal cavity is pressurized with helium and a hand-held helium leak detector hose "sniffs" the seal areas to detect escaping helium.
Evacuating the specimen's inner chamber is the most commonly called for test method we see. The sizes of our customers' parts are relatively small so evacuating the inner chamber is a relatively quick operation. We design and manufacture the unique seal connections required to plug seal openings and also to connect to the vacuum pump.
The benefits of helium leak testing are that helium is inert, its small atomic size allows it to pass through very small leaks and helium has a naturally low quantity presence in air simplifying testing since it is not present as a background gas that must be compensated for in the test set up.
Helium leak testing is an alternative to hydrostatic pressure testing. It is a dry process and the inert nature of helium precludes the concern of contaminating the test specimen. Also, helium leak testing allows leaks to be quantified based on the pressure differential across the leak and the helium count rate. Hydrostatic pressure testing on the other hand produces an absolute result: passed or failed.
The most common application we see from customers for helium leak testing is for performing quick intermediate leak tests on a sub-assembly that will be welded in place into a larger assembly. If a leak exists in the sub-assembly and it is not found until welded into the larger assembly, disassembly costs and delays can be high enough to justify testing the sub-assembly prior to installation into the larger assembly.