4. Penetrant testing

4.1 Principle

Penetrant testing is a term used to describe the extraction of a fluid from a discontinuity in which it has previously accumulated during an impregnation operation. Impregnating a crack with a liquid, taking advantage of its tensio-superficial properties, leads, by means of penetrant testing prior to visual observation, to a means of searching for surface defects that is among the oldest, simplest and most widely used today.

The mechanism for revealing defects by penetrant testing corresponds to the three phases illustrated in figure 7 : application of the penetrant followed by an impregnation time, removal...