Dye penetrant inspection
![1. Section of material with a surface-breaking crack that is not visible to the naked eye.2. Penetrant is applied to the surface.3. Excess penetrant is removed.4. Developer is applied, rendering the crack visible.](/Images/godic/202501/10/Ressuage_principe_2.svg5430.png")
![Application of the penetrant to a part in a ventilated test area.](/Images/godic/202501/10/KD-Check_Anwendungsbild5430.jpg")
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.