Liquid penetrant testing is yet another form of nondestructive testing used for finding surface defects only. Penetrant testing is a physical and chemical test used for detecting and making visible to the naked eye surface related discontinuities in non-porous materials.
Solvent removable penetrant is the most common application. Evaluation is made with white ambient light.
Water washable penetrant is a rapid and effective means of inspecting large areas or in locations where the solvent would have an injurious effect upon the material or personnel. The inspection is usually made with white light.
Fluorescent penetrant removable both by solvent or water and with evaluation made under ultraviolet light is the most sensitive of the penetrant methods for inspection. A darkened environment is necessary for inspection under the black light.