Leak detection

What is sealing? Tightness is the quality of a closed enclosure that does not allow any fluid to pass through its walls. Obtaining and maintaining such a property is, in reality, a gradation of operations, and the hermeticity of an enclosure must be considered, even from a theoretical point of view, as illusory.

A perfectly homogeneous structure can be permeated by gases, due to sorption and desorption at the solid's interfaces, and solution and diffusion within it. This complex process, known as permeation, varies greatly according to the nature of the elements involved. Gas permeation through metals, for example, is not usually likely to affect sealing, whereas gas permeation through elastomers can lead to ambiguities in leak detection. In what follows, we will only be concerned with leakage, i.e. the transfer of fluids, which is not a diffusion or permeation phenomenon.

On the other hand, all industrially-manufactured products must satisfy a necessary and sufficient level of leak tightness. In most cases, very small leaks are acceptable in terms of the safety and life expectancy of the manufactured product. It will then be necessary to define a rejection threshold in the context of leak testing, i.e. to define the largest acceptable leak to declare a part "good". Accepting the idea that a manufactured product may leak to a negligible extent is often the first difficulty in taking the first steps towards leak detection.

This article is a reworking of Jacques Tallon's previous article. The author has reproduced large parts of it, in particular the theoretical study. Readers are also invited to consult [B 5 420] – Génie mécanique des Techniques de l'Ingénieur.