The liquid penetrant examination method is an effective means for detecting discontinuities which are open to the surface of nonporous metals and other materials such as plastics, glass, and ceramics. Typical discontinuities detectable by this method are cracks, seams, laps, cold shuts, laminations, and porosity.

The liquid penetrant contains either a coloured dye easily seen in white light, or a fluorescent dye visible under black (ultraviolet) light. The penetrant is applied by dipping, spraying, brushing, or flowing. After penetrant application, a sufficient time (dwell time) is provided to permit the penetrant to permeate the flaw.

Dexon Penetrant Testing Videos:

Penetrant Testing (PT) – NDT Inspection Technique                

Fluorescent Penetrant Testing – NDT Inspection Technique

Prior to each liquid penetrant examination, the surface to be examined and all adjacent areas within at least 1 in. (25 mm) shall be dry and free of all dirt, grease, lint, scale, welding flux, weld spatter, paint, oil, and other extraneous matter that could obscure surface openings or otherwise interfere with the examination.

The liquid penetrant can be examined by PT or FPT method, for the highest sensitivity a fluorescent Penetrant in combination with a black light is available. PT can only find surface breaking defects, needs a very thorough surface preparation and has a high sensitivity. This cleaning and preparation does result in fluids and contaminated cleaning materials that do need to be correctly disposed of after use

This testing method is capable of finding very small flaws and can be used on different materials and small, difficult shaped objects. As the liquid penetrant testing technique is relatively simple it is easy to understand and training is not extensive.