Hydrogen leak testing is the normal way in which a

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

pressure vessel or installation is checked for

leak A leak is a way (usually an opening) for fluid to escape a container or fluid-containing system, such as a tank or a ship's hull, through which the contents of the container can escape or outside matter can enter the container. Leaks are usually ...

s or flaws. This usually involves charging hydrogen as a tracer gas into the device undergoing testing, with any leaking gas detected by hydrogen sensors. Various test mechanisms have been devised.

Test mechanisms

Hydrostatic test

In the

hydrostatic test A hydrostatic test is a way in which pressure vessels such as pipelines, plumbing, gas cylinders, boilers and fuel tanks can be tested for strength and leaks. The test involves filling the vessel or pipe system with a liquid, usually water, wh ...

, a vessel is filled with a nearly incompressible liquid – usually

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

– and examined for leaks or permanent changes in shape. The test pressure is always considerably higher than the operating pressure to give a margin for safety, typically 150% of the operating pressure.

Burst test

In the burst test, a 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.

Helium leak test

The helium leak test uses

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

(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, is inert and will not react with the test piece while having a naturally low quantity in air making detection less complicated. It is possible to detect leaks as small as 5x10⁻¹⁰ Pa·m³/s in vacuum mode and modern digital machines can detect 5x10⁻¹⁰ Pa·m³/s in sniffing mode.

Vacuum test

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.

Hydrogen sensor test

During the hydrogen sensor test, the object is filled with a mixture of 5%

/ 95%

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

, (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. Compared to the helium test, hydrogen is cheaper than helium, no need for a vacuum, the instrument could be cheaper but is not as sensitive as a helium leak detector so will not find smaller leaks. Chemo-chromic hydrogen leak detectors are materials that can be proactively applied to a connection or fitting. In the event of a hydrogen leak, the chemo-chromic material changes color to alert an inspector that a leak is present. Chemo-chromic indicators can also be added to silicone tapes for hydrogen detection purposes.

References

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External links

Leakpedia – The free wiki encyclopedia about the industrial leak testing

Detectape – Hydrogen detection silicone tape
Hydrogen technologies Tests Hydrogen Nondestructive testing