Hydrogen leak testing

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Hydrogen leak testing is how engineers check hydrogen vessels and installations for leaks or flaws. It often uses hydrogen as a tracer gas and sensors to detect leaks. Several methods are used:

Hydrostatic test
- The vessel is filled with a nearly incompressible liquid, usually water or oil.
- It is checked for leaks and for permanent changes in shape.
- The test pressure is higher than normal operating pressure to add safety, typically about 1.5 times the operating pressure.

Burst test
- The vessel is filled with a gas and tested for leaks.
- The test pressure is kept well above the operating pressure, typically around 2 times or more the operating pressure, to provide a safety margin.

Helium leak test
- Helium is used as a tracer gas because it is inert, penetrates small leaks easily, and is easy to detect.
- Leaks can be detected at extremely small levels. In vacuum mode, very tiny leaks can be found; modern systems also detect very small leaks in sniffing mode.
- The test usually involves creating a vacuum or placing the part in a vacuum chamber and using detectors to find where helium escapes.

Hydrogen sniffing test
- The object is filled with a mixture of 5% hydrogen and 95% nitrogen (below 5.7% hydrogen, which keeps it non-flammable per ISO-10156).
- A hand-held probe and sensors listen for a leak by detecting hydrogen, often with an audible signal when a leak is nearby.
- This method detects leaks down to about 5 x 10^-7 cubic centimeters per second.

Chemo-chromic detectors
- Some leak-detection materials change color when they contact hydrogen, signaling a leak.
- These indicators can be applied to fittings or used in silicone tapes for hydrogen detection.

Comparison
- Hydrogen testing using sniffing methods is cheaper and does not require a vacuum, but it is generally less sensitive than helium leak testing.
- Helium leak testing is extremely sensitive but more expensive and may require vacuum equipment.