Up to 1000x more sensitive than pressure decay testing is only one of the many advantages of switching from pressure decay leak testing to using the Gas –FET (Gas – Field Effect Transistor) diluted hydrogen method. Pressure decay systems are limited in sensitivity to, typically, a pressure drop of 0.01 mbar/sec (0.0001 psi/sec) for ideal conditions. For a test volume of 100cc this equates to a leak flow rate of 1x 10-3 cc/sec and for a test volume of 1,000cc it equates to a leak flow rate of 1x10-2 cc/sec. As previously stated to be able to test to these limits the test object conditions have to be ideal – no flexing due to elastic materials (flexing increases volume and therefore changes the pressure) – no temperature changes, temperature changes may be due to the part being hot from a manufacturing process (welding) or due to pressurizing the object (a temperature change will result in a change in pressure). The effects of both of these conditions can be calculated using the Ideal Gas Law - P1.V1/T1 = P2.V2/T2. Volume or temperature changes may result in false positive or negative test results.
Walwyn Jackson, Leak Detection Service Supervisor
Walwyn.Jackson [at] inficon.com
The Gas-FET method as well as being at least 3 orders more sensitive (5x10-7 cc/sec) than pressure decay testing for the conditions stated above will also address the other pressure decay testing drawbacks.
1/The test is not component volume dependent - the high sensitivity is the
of the test volume.
2/The test is not affected by flexing or creep of the test object – the test is measuring the actual leakage flow rate from the test object and not the resultant pressure change
3/The test is not affected by the temperature of the part - the test is measuring the leakage flow rate from the object and not the resultant pressure change
4/The test will pinpoint the leak position.