Checklist: 10 avoidable mistakes in leak testing

The checklist is intended to help find the right methodology in leak testing. For example, the (wrong) choice of leak test method, such as the water bath method, can cause the tester to miss leaks because he has not considered the deformability and volume change of the test part. Inficon has summarized which mistakes companies can avoid during leak testing in a top 10 checklist of avoidable leak testing mistakes.

Error 1: The wrong method for the leak rate to be tested

A common error with the water bath method is that the tester does not detect bubbles even though there is a leak. Problematic: A basic condition for determining whether a leak test or leak detection method is suitable is the limiting leak rate. Often, however, companies do not pay attention to this in practice. For example, they inspect plastic parts using the pressure decay method without considering their deformability and the volume change caused by the compressed air. The leak rates of the integral leak test and subsequent leak detection must match.

Error 2: Incorrectly selected test time in the production process

At what point in the production process does a leak test make sense? This should be considered carefully. It is usually helpful to check subcomponents before they are assembled. If the pre-assembled components fail the series test, the effort is significantly higher - and the working time invested in the assembly is lost.

Error 3: The test part is contaminated

The following applies to all test methods: Leak tests should always be carried out on completely new test parts. If a component was already in operation beforehand and, for example, filled with oil or water, small leaks may have become clogged. Before a leak test, companies must clean the test parts and then dry them.

Error 4: Temperature changes are not taken into account

For integral leak tests based on the principle of pressure drop or differential pressure measurement, temperature fluctuations are serious. Minimal temperature changes can alter the measurable leak rates by several orders of magnitude.

Error 5: The test pressure fluctuates

Companies should always fill the test part with the same constant pressure during the leak test. Caution is advised, however, as for some test parts correct filling is only possible after prior evacuation. In helium testing, for example, tracer gas concentrations are reduced in order to lower testing costs.

Mistake 6: Creep leaks and groble leaks are underestimated

Creep leaks consist of capillary-like passages. For a successful test, it is necessary to consider how long it takes for the tracer gas helium to distribute itself in such a way that it also escapes from creep leaks. Therefore, there should be sufficient time between filling and testing to be able to reliably identify creep leaks.

Error 7: The auditors do not know how to measure

For an integral leak test, it is recommended to use a reproducible measurement method instead of relying only on the perception of the tester. But one should consider how one measures and with which test medium. For example, leak rates are specified for air, but helium has a slightly higher dynamic viscosity than air. Therefore, a conversion is needed for the exact leak rate.

Error 8: There is no calibration of the test equipment

Companies should regularly check the functioning and accuracy of a system with a reference leak (e.g. a test leak in a glass capillary), which always causes the same leak rate due to its defined size. If this leak rate is not determined in the test, the plant has a problem.

Error 9: The maintenance of the test equipment is neglected

If companies do not measure leak rates at a test station for days or even weeks that are greater than those at which the test part still passes the test, this is either a sign of the immense quality of the product - or also an indicator of an inadequately functioning test facility. For this reason, companies should regularly check joints, hoses, test part fixtures etc.

Mistake 10: "We can do it ourselves"

This is something you should think about carefully. It is better to turn to experts for comprehensive advice. Choosing the right test method, configuring equipment correctly and making test processes as foolproof and reliable as possible is a major challenge - which is why professional support is recommended.

The top 10 most common leak testing mistakes are an excerpt from Inficon's free e-book, "Leak Testing of Refrigeration, Air Conditioning and Heating Systems - A Guide," which you can download at here free of charge.

www.inficon.com