Trace gas leak detection is a non-destructive testing method for pinpointing the exact location of a pipe break or leak. A tracer gas is introduced into the system and tracked as it escapes from the test object. This provides a more precise result than acoustic leak detection, which relies on the sound of escaping air, water or gas, and can be difficult to perform in noisy environments.
The ideal tracer gas for testing has very small molecules so that it can pass through the smallest leak paths, is absent from the surrounding atmosphere to make the process easier and can be detected by sensitive gas detectors (sniffers). Helium is often used for this purpose as it is odourless and inert, reducing the risk of accidental inhalation. Other gases that can be used as tracers include HFC and CFC compounds used as refrigerants, as well as the inert gases nitrogen and carbon dioxide.
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When conducting a trace gas test, the test item is filled with the tracer gas at a pressure higher than atmospheric and a sniffer probe connected to the leak detector is moved over the critical areas. If a leak is present, the tracer gas will be sucked through the leak path and into the sniffer probe. The resulting signal is then processed by the leak detector to calculate and display the current leak rate.
Another popular method for tracer gas testing is carrier-gas leak testing, which eliminates the need for a large test chamber. Instead, a stream of tracer-gas-free carrier gas is swept through the test item and analyzed by the leak detector to produce a real-time leak rate. The test is particularly suitable for smaller parts and offers the same precise results as the vacuum integral method with a shorter cycle time.