This inspection method is used to locate surface-breaking defects in all non-porous materials. PT is used to detect casting, forging, and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components. Penetrant Testing is based upon capillary action, where low surface tension fluid penetrates into clean and dry surface-breaking discontinuities. The penetrant may be applied to the test component by dipping, spraying, or brushing. After adequate penetration time has been allowed, the excess penetrant is removed and a developer is applied. The developer helps to draw penetrant out of the flaw so that an invisible indication becomes visible to the inspector. Inspection is performed under ultraviolet or white light, depending on the type of dye used –fluorescent or non-fluorescent (visible).
