Penetrant testing is a non-destructive testing method used to detect casting, forging, and welding surface defects such as hairline cracks, surface porosity, leaks in new products, fatigue cracks on in-service components, and locate surface breaking discontinuities in non-porous materials (metals, plastics, or ceramics). This method may be applied to ferrous and non-ferrous materials, although for ferrous components magnetic-particle testing is often used instead for its subsurface detection capability.
