penetrant inspection (DPI), also called liquid penetrant inspection (LPI) or
penetrant testing (PT), is a widely applied and low-cost inspection method used
to locate surface-breaking defects in all non-porous materials (metals,
plastics, or ceramics). The penetrant may be applied to all non-ferrous materials
and ferrous materials. Dye penetrant inspection 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 may be
applied to the test component by dipping, spraying, or brushing. 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 nonfluorescent (visible).