Dye penetrant inspection is a means of locating fine cracks on the surface of parts by allowing a visible or fluorescent dye to accumulate in any such discontinuity to reveal its shape and location. The technique is applicable to virtually any non-porous material.
Dye penetrant inspection is a three-step process beginning with the application of a visible or fluorescent dye to the clean, dry surface of the test specimen. In a short time the penetrant is drawn into any surface depressions or voids by capillary action. After a pre-determined interval the excess penetrant is removed and a developing agent is applied to the surface. The developing agent draws the remaining penetrant out of the cracks to make them readily visible to an inspector. This technique can be used to detect surface flaws on essentially any non-porous material.