ABSTRACT
Penetrant inspection utilizes the natural accumulation of a fluid around a discontinuity to create a recognizable indication of a crack or other surface opening. Capillary action attracts the fluid to the discontinuity in a concentration heavier than in the surroundings. In order for the fluid concentration to be recognized, the background area must be of sufficient contrast to distinctly reveal the defect on the surface. The complete penetrant flaw detection system, therefore, consists of the fluid mechanics on the surface, as well as the recognition system that is used to detect the indication. A typical example of the principles involved in penetrant inspection is the ready visibility of cracks in concrete stabs shortly after a rain. After the sun has reappeared and the thinner surface water has evaporated, the heavier water concentration remaining around the cracks clearly reveals their location and shape.
