MEASUREMENT PRINCIPLE OF HYDROGEN LEAK TEST

The hydrogen leak test is a testing device that detects leak by charging gas that includes hydrogen in the tested work and detecting leaked gas using a hydrogen sensor.

Tracer Gas

Hydrogen is used as the tracer gas for the hydrogen leak test. Industrial mixed gas of hydrogen 5% + nitrogen 95% is recommended to be used as the tracer gas. It can be used safely since the industrial mixture of hydrogen 5% + nitrogen 95% is defined as non-flammable gas. (ISO10156:2017)
*Although highly-concentrated hydrogen gas can be used, it is not defined as non-flammable gas.

Principle of Detection

The hydrogen detection sensor used for the hydrogen leak detector applies a semiconductor type gas sensor with a sintered structure in which tin oxide is vitrified. The semiconductor type gas sensor does not allow electricity to flow in normal room temperature. Electricity starts to flow when the sensor is in high temperature of approximately 400°C by a heater in an ambient with no oxygen. 　Oxygen in the atmosphere is adsorbed to the sensor surface of the hydrogen leak detector when measured in the atmosphere. The adsorbed oxygen inhibits the flow of electron causing high electric resistance and a condition where electricity is difficult to flow. When hydrogen gas is sucked during the measurement, hydrogen molecules attach to oxygen (oxidation reaction) and oxygen attached to tin oxide decreases. Since the amount of oxygen on the sensor surface decreases, the electric resistance value decreases and electricity starts to flow easily. Leak of hydrogen gas and gas concentration are detected through this change of electric current.

[Figure]　Principle of Hydrogen Leak Test

Applicable product

Measurement Method of Hydrogen Leak Test