Dye 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, although for ferrous components
magnetic-particle inspection is often used instead for its subsurface detection capability. LPI 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.