What is penetrant?

Penetrant testing (PT), also called liquid penetrant inspection (LPI) or dye penetrant inspection (DPI), is a widely used non-destructive testing (NDT) method used to detect surface-breaking defects in non-porous materials (metals, plastics, ceramics). It involves applying a visible or fluorescent dye to the surface of the part, allowing it to penetrate into defects, removing excess penetrant, and then applying a developer that draws the penetrant out of the defects, making them visible to the inspector. It's commonly used for detecting cracks, porosity, laps, seams, and other surface flaws in welds, castings, forgings, and machined parts.