Leak test methods are very varied and depend on the level of precision required. It is always necessary to specify the required tightness level, because a perfect tightness is not always possible or necessary!
Pressurising a system with a fluid (water = hydraulic or gas = pneumatic) and monitoring pressure maintenance is the most common technique.
Conversely, the vacuum pulling of an area (e.g. the welding between 2 plates) and the control of the evolution of this vacuum also makes it possible to decide on the tightness of the area (vacuum box).
Ultrasonic techniques can then be used to listen to or detect leaks when a tank is subjected to a partial vacuum (Tank Test SDT).
Finally, for high precision, the detection of a tracer gas such as Helium makes it possible to detect the smallest leaks.
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