30 January 2012

Weld leak testing

Carr’s welding technologies are well known for their laser welding services, but increasingly Carr’s have to test the jobs that they are welding. Carr’s have 5 production jobs that they helium test, for example, an Inconel core which has dozens of welds, has to be tested at 3 stages during the assembly and welding process. I.e. some of the initial welds are covered by sequential welds and so we have to test the welds for quality before we can proceed to the next weld.

Helium testing works on the idea that Helium is a tiny element and if there is a hole in a welded joint, it is the best gas to squeeze through and detect the leak. Generally Carr’s pump the air out of the enclosed space that has been created by welding 2 or more parts together. When a vacuum has been created in the body of the job, the analysers is switched on. This looks at the rarefied atmosphere inside the assembly. Any Helium inside the job can be easily detected and quantified. For example; welding a connector into an assembly plate or casting.

Once evacuated the helium is introduced on the outside of the welded area with a small jet or needle. If a leak is detected the analyser will show an increased level of helium inside the job. The screen shows a long line and the machine beeps. This way a hole is pinpointed and a repair of the leak can be instigated. Once repaired the assembly is retested until no leaks are detected.
Helium leak testing is part of the welding process quality valuation and is not offered as a service on its own.

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