Trace gas helium for leak testing
The helium leak test is based on the detection of helium as the test gas, which only occurs in the ambient air in a very low natural concentration of approx. 5 ppm. Therefore, a reliable test statement is possible even by detecting a small amount of helium. Before a helium leak test, a rough leakage measurement is usually carried out first.
The test chamber is evacuated and the test specimen is pressurised with helium. Helium escaping through leaks is sucked in by a high vacuum pump and detected.
The test specimens are either filled with helium before sealing or subsequently subjected to helium overpressure for a certain time so that helium penetrates the test specimen. This is followed promptly by testing in a vacuum test chamber, where the amount of escaping helium is determined. A mass spectrometer, which consists of an ion source, the separation system and the ion detector, serves as the detection system for the test gas.
Tracer gas Helium
- Occurs in nature only atomically, builds no molecules. Chemically inertly due to its (only) completely occupied valence electron shell.
- After hydrogen the secondly most frequent element in the universe.
- Natural gas contains on the average 0,4% He and is thereby the economically most important source for the helium production.
- By all gases Helium is the most difficult to liquefy and cannot be converted in solid state at normal pressure. At 30 bar: Freezing point -271.4 °C; Boiling point at normal pressure is -269 °C.
- Density (20 °C): 0.1664 gram/liter
- Mol mass: 4.003 u (small, light molecule, which passes easily small leakages)
- moderate price for industrial applications
Some applications of helium:
- Inert gas for welding light metals and alloys
- filling gas for balloons
- additive to the breathing air when deep diving against the diver´s palsy
- Medical technology; in case of breathing problems
- Ion beams from Helium nucleus to mediate eye or cerebral tumors