Why leak test? Leak testing is performed to ensure that when in service, the component or assembly has zero leakage or a leakage that is acceptable over time for the fluid/gas that it is meant to contain, or conversely to prevent material on the outside from leaking in. A component or assembly leaking in operation above the limit specified would at best incur the cost of replacement, tarnishing the manufacturer’s reputation and at worst may lead to a devastating failure of the system. One point to note is that all things leak to some degree, however, the reason to leak test is not to stop all leaks but to test to a standard that will ensure the tested part will not leak the product inside or not exceed an allowable leak rate in service. The test method chosen to perform this critical test requirement that ensures a part does not leak is dependent on many factors including:
(a) The direction of leak – from inside out or from the outside in.
(b) The media contained inside the part and if the requirement calls for zero leakage or an acceptable leak rate over a time period.
(c) The viscosity of that substance that the part will contain in service – this will be a major contributor in calculating the sensitivity required of the test.
(d) The pressure that the test piece will see in service – particularly important when the part is flexible or features O ring joints that may move and reset at variable pressures.
(e) The requirement to measure the total leak rate (global test – chamber test) or to pinpoint the leak site (sniffing).
(f) The internal volume of the test piece.
(g) The hole size that has been determined to prevent the substance from leaking out or into the test part or assembly.