# 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

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.