Physics:Tracer-gas leak testing

Short description: Nondestructive testing method for detecting gas leaks

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

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.