Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI) or penetrant testing (PT), is a widely used and also is low-cost inspection method. It is used to locate defects open to the surface in all non-porous materials (metals, plastics, or ceramics), non-ferrous materials and ferrous materials. Although for ferrous components magnetic-particle inspection is often used. LPI is used to detect surface defects in casting, forging and welding, such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.