A non-destructive testing process in which a penetrating agent is used to detect weld defects and other possible flaws in non-magnetic materials. Liquid penetrant inspection is accomplished in a three-step method for preparation and testing. First, a cleaner is sprayed on the part to be tested and all dirt and grease removed; the penetrant is applied and the excess removed; then the developer is sprayed on. The developer, on drying, draws the penetrant to the surface and the flaws will show up in natural light. Many of the dye penetrants are packaged in spray cans for convenient use.

A variation of the dye penetrant method of inspection is the fluorescent penetrant method. This system requires ultraviolet light (black light) to reveal defects. If there are defects, they appear in sharp glowing contrast to the surrounding flaw-free surface.

The fluorescent penetrant is an oil-base agent with suspended fluorescent particles capable of penetrating every surface defect. It is applied by dipping, spraying or brushing on the piece to be inspected. After it has entered any of the seams, cracks and pinholes, the surface excess is washed away with a water spray. When it has dried, a dry powder of water-suspension developer is applied to create a dry powder film on the surface. This draws the penetrant up from the defect. The inspection is done under a black light in a darkened booth. See MAGNETIC PARTICLE INSPECTION.

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