Helium leak testing is one of the oldest and most developed members of the family of trace-gas-based leak testing methods. Even though the title contains the word “helium,” this article is intended as an overview of trace gas methods in general.
Trace gas methods measure leaks directly, i.e. they aim to determine the quantity of material escaping from the part under test. This is in contrast with other, non-trace-gas-based methods that measure the effects of the leak (as is the case with pressure-decay leak testing). Because of this, these methods are generally capable of measuring very small leaks and can be used to test large or complex parts because part volume has no direct effect on the reliability of the test.