Tracer-gas leak testing method

Tracer-gas leak testing method is a nondestructive testing method.

Types

Several tracer-gas leak testing methods exist among which the methods of choice are:

• Helium mass spectrometer or helium leak detection, providing the highest sensitivity
• Hydrogen leak testing or hydrogen leak detection, providing the best mobility
• Refrigerant gas leak detection, for refrigeration applications.

Method selection

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

Typical leak rates

System	Allowed Leak Rate	Comments
Chemical process equipment	10−1 to 1 mbar l/s	high process flows
Beverage can	low 10−5 to 10−6 mbar l/s	retention of CO2
Vacuum pumped system	10−5 to 10−7 mbar l/s	permanent pumping
IC-package	10−7 to 10−8 mbar l/s	lifetime control
Airbag cartridge	10−8 mbar l/s	lifetime control
Pacemaker	10−9 mbar l/s	Bio compatibility
Closed vacuum system	10−9 mbar l/s	X-Ray tube

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

Leak test performances

mbar l/s	102	101	100	10−1	10−2	10−3	10−4	10−5	10−6	10−7	10−8	10−9	10−10	10−11	10−12
Bubble test in water	----	----	----	----	>
Bubble test soapy water	----	----	----	----	----	----	>
Pressure decay	----	----	----	----	----	>
Acoustic (US)	----	----	----	----	----	>
Vacuum decay	----	----	----	----	----	>
Corona tester	----	----	----	----	----	>
Thermal conductivity	----	----	----	----	----	----	----	>
Halogen sniffer*	----	----	----	----	----	----	----	>
Hydrogen sniffer	----	----	----	----	----	----	----	----	->
Helium sniffer	----	----	----	----	----	----	----	----	->
Halogen detector*	----	----	----	----	----	----	----	----	>
Dye penetrant	----	----	----	----	----	----	----	----	----	----	>>
Radio-isotope	----	----	----	----	----	----	----	----	----	----	----	----	>>>>
Mass spectrometer	----	----	----	----	----	----	----	----	----	----	----	----	----	>>>>>>

• Restriction of use (F-Gas Directive)

Typical applications of tracer gas leak testing include:

• Chemical plant
• Petrochemical plant: hydrocracker, vapocracker, catalytic reforming, steam reforming are all Hydrogen based processes were Hydrogen leak testing will be very appropriate,
• Semiconductor industry; all processes taking place in a process chamber at atmospheric pressure or under vacuum; Diffusion, Oxidation, LPCVD, PECVD, PVD, Etch, Ion Implant, typically the later that implies vacuum will require Helium leak testing, while the other will make good use of Hydrogen leak testing,
• Automotive: with airbag being the most demanding leak testing application (small gas tank, very high pressure, long shelf life) and air conditioning system (for best efficiency), fuel system (for low emission), exhaust system (for lowest pollution), engine and transmission (for no oil dripage), rims to keep tyre safe,
• Medical: to ensure safe and long life implant (pacemaker) or a safe catheter
• Airplane: to quickly and safely locate fuel leaks, to check oxygen distribution devices and cabin pressurization systems
• Refrigeration and air conditioning systems-residential, commercial or industrial- in order to deliver best efficiency at the lowest loss rate of refrigerant gases (ozone depletion)
• Power distribution for high voltage circuit breaker using SF₆ as a dielectric
• Drinking water distribution grid as today average leakage rate or efficiency is above 25%, wasting precious resources, water and power.
• Sewage water collecting network as leaks can contaminate drinking water collection process;

Another element of consideration is the dimension of the part to be tested as well as to take into consideration the law of physics, specially the rules that govern the flow of gas at different pressure. <<stub>>

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.