Tracer-gas leak testing

A tracer-gas leak testing method is a nondestructive testing method that detects gas leaks. A variety of methods with different sensitivities exist. Tracer-gas leak testing is used in the petrochemical industry, the automotive industry, the construction industry and in the manufacture of semiconductors, among other uses.

Types

Several tracer-gas leak testing methods exist, including:

• Detection of leaks using helium mass spectrometer, which provides high sensitivity
• Hydrogen leak testing, which provides the best mobility
• Refrigerant gas leak detection, for refrigeration applications

Method selection

Typical leakage rates

The nature of the product or the process and the process gases will set the leak rate requirement:

System	Allowed leak rate (mbar L/s)
Chemical process equipment	10−1–1
Beverage can	10−5 –10−6
Vacuum pumped system	10−5–10−7
IC-package	10−7–10−8
Airbag cartridge	10−8
Pacemaker	10−9
Closed vacuum system	10−9

Sensitivity of methods

Based on the target leak rate, the table below will help to choose the most suitable method.

Method	Sensitivity (leak rate in mbar l/s)
Ultrasonics	10−1
Bubble test in water	10−2
Pressure decay	10−2
Vacuum decay	10−2
Acoustic emission detectors	10−3
Bubble test in soapy water	10−4
Gas-specific thermal conductivity detector	10−5
Halogen detector	10−5
Photoacoustic spectroscopy	10−6
Hydrogen sniffer	10−6
Residual gas analyser	10−7
Dye penetrant	10−8
Radioactive tracer	10−10
Helium mass spectrometry vacuum testing	10−11

Applications

Typical applications of tracer-gas leak testing include:

• In petrochemical plants, hydrocracking, vapocracking, catalytic reforming, and steam reforming are all hydrogen-based processes, in which were hydrogen leak testing is required.
• When manufacturing semiconductors, all processes taking place in a process chamber at atmospheric pressure or under vacuum – diffusion, oxidation, LPCVD, PECVD, PVD and ion implantation – require helium or hydrogen leak testing.
• In vehicles, airbags have to be tested for leaks so they remain functional for a long time. As well as airbags, the air conditioning system, fuel system, and exhaust system require testing for leaks.
• Pacemakers and catheters have to be tested for efficacy and longevity.
• On planes, tracer-gas leak testing is used to quickly and safely locate fuel leaks, as well as to check oxygen distribution devices and cabin pressurization systems.
• Refrigeration and air conditioning must have the lowest possible rate of loss of refrigerant gases (contributing to ozone depletion).
• Sewage and drinking water networks, to reduce loss of water and make sure drinking water is not contaminated by sewage.

Standards

See also: Leak detection § Rules and regulations

Several standards apply to leak testing and more specifically to tracer-gas leak testing methods, for example:

• BS EN 1779:1999; leak tightness by indication or measurement of gas leakage,
• BS EN 13185:2001 Non-destructive testing. Leak testing. Tracer gas method,
• BS EN 13192:2002 Non-destructive testing. Leak testing. Calibration of reference leaks for gases.