Leak testing

What is Leak testing

 Leak Testing is a procedure that inspectors use to determine whether an object or system is functioning within a specific leak limit. Leaks occur when there is a defect—a hole, crack, or some other kind of flaw—in an object, allowing whatever the liquid or gas it is holding to flow out.

In leak testing, inspectors use pressure to identify the presence of defects in an object that are causing leaks.

When substances leak out of a container they flow from where the pressure is higher pressure to where it is lower. Leak testing leverages this phenomenon, using pressure to generate flow toward lower pressure—that is, the location of leaks—while carefully monitoring that flow. 

When should leak testing be performed? Primarily when testing for flaws within a closed system.

The success of a leak test depends on the object that is being tested. Different types of materials and objects may respond differently to the high pressures typically used in leak testing to force a liquid or gas out of a defect, thus revealing its presence and location. 

The leak test is performed by immersing a part, usually a sandwich composite structure, in a hot water tank. The temperature of the water induces the expansion of air in the structure, and if a crack or a delamination is present, gas bubbles escape the structure and are immediately detected by visual inspection. A leak test is easy to set up for small parts and only requires simple equipment. It is limited by the resolution of the human eye, and can only lead to the detection of an emerging surface crack or delamination. The leak test is a standardised NDT technique in most aeronautic manufacturers. Due to its limitations, basic applications include the inspection of delaminations and disbonds in sandwich composite structures, especially honeycomb core.

Helium and hydrogen are typically used when testing large volumes, such as fuel tanks.

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