Tracer gas leak detection
| Tracer gas leak detection | |
| Type | Detection method |
|---|---|
| Gas used | Typically 5% hydrogen in nitrogen |
| Detects | Gas escaping at the leak point |
| Requires | The system to be drained and isolated |
| Used where | Acoustic methods fail or the system cannot hold pressure |
Tracer gas leak detection introduces a safe gas mixture into a drained pipe or system and detects it at the surface where it escapes. Because the method depends on the gas finding its way out rather than on noise or heat, it works on systems that cannot be pressurised with water, on very small leaks that produce no audible signal, and on pipework buried under solid floors where other methods are ambiguous. No statute or published standard defines the technique, so the description below is of established industry practice and carries no citation.
Principle[edit]
The system is drained, isolated and charged with the tracer mixture, most commonly hydrogen diluted in nitrogen at a concentration low enough to be non-flammable. The gas is far less dense and less viscous than water, so it escapes through openings too small to produce a useful leak noise and migrates upwards through soil, screed and floor coverings to the surface. A hand-held detector is then passed over the area and responds where the concentration rises.
The rise in concentration marks where the gas reached the surface, which is not always directly above the escape. Gas follows the path of least resistance and can travel along a pipe trench, a service duct or a crack in a slab before emerging.
Applications[edit]
Tracer gas is the usual method where a heating or plumbing system will not hold pressure long enough for acoustic work, where a leak is beneath a solid floor, and where a previous acoustic or thermal survey has narrowed the area but not fixed the point. It is also used on pressurised supply pipes when the escape is too small to be heard.
Practical constraints[edit]
The system must be drained, which takes time and means the property is without that service during the test. Surfaces have to be reasonably undisturbed while readings are taken, since ventilation disperses the gas. Impermeable coverings such as sealed vinyl or thick adhesive can delay or prevent the gas reaching the surface, in which case small access points are made at intervals.
Refilling and recommissioning the system afterwards is part of the work, and on sealed heating systems this includes re-pressurising and venting.
See also
- Water leak detection
- Acoustic leak detection
- Pressure testing
- Underfloor heating manifold
- Push-fit fitting