Hydrogen leak testing
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Hydrogen leak testing is the normal way in which a hydrogen pressure vessel or installation is checked for leaks or flaws. There are various tests.
- The Hydrostatic test, The vessel is filled with a nearly incompressible liquid - usually water or oil - and examined for leaks or permanent changes in shape. The test pressure is always considerably more than the operating pressure to give a margin for safety, typically 150% of the operating pressure.
- The Burst test, The vessel is filled with a gas and tested for leaks. The test pressure is always considerably more than the operating pressure to give a margin for safety, typically 200% or more of the operating pressure.
- The Helium leak test, The leak detection method uses helium (the lightest inert gas) as a tracer gas and detects it in concentrations as small as one part in 10 million. The helium is selected primarily because it penetrates small leaks readily.
- Usually a vacuum inside the object is created with an external pump connected to the instrument.
- Alternatively helium can be injected inside the product while the product itself is enclosed in a vacuum chamber connected to the instrument. In this case Burst and leakage tests can be combined in one operation.
- The Hydrogen microsensor, The object is filled with a mixture of 5% hydrogen/ 95% nitrogen, (below 5.7% hydrogen is non-flammable (ISO-10156). This is called typically a sniffing test. The handprobe connected to the microelectronic hydrogen sensors is used to check the object. An audiosignal increases in proximity of a leak. Detection of leaks go down to 5x10-7 cubic centimeters per second [1]. Compared to the helium test: hydrogen is cheaper than helium, no need for a vacuum, the instrument could be cheaper.
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[edit] Uses
[edit] Room testing
Stationairy unit, Hydrogen gas is only 7% the density of air, and thus rises. The hydrogen gas detector should be installed at the highest draft-free location in the room or compartment where hydrogen gas would accumulate.
[edit] In-Line testing
A fixed stationary unit on the assembly line or installation. Chemochromic Sensors
[edit] Hand held testing
A light mobile point-contact sensor
Hydrogen Concentrations of 4% to 75% mixed with air (around 40,000 ppm) can be explosive.
