Liquid penetrant testing can be used to detect surface defects in both non-ferromagnetic and ferromagnetic materials. During liquid penetrant testing, the object or material is coated with a visible or fluorescent dye solution. Excess dye is removed from the surface and then a wet or dry developer is applied. The developer acts as a blotter drawing the penetrant out of imperfections open to the surface. With visible dyes, the color contrast between the penetrant and the developer make the penetrant bleedout easy to see. With fluorescent dyes, ultraviolet light is used to make the bleedout fluoresce brightly, thus allowing imperfections to be seen readily. TPT utilizes liquid penetrant testing to detect surface defects such as porosity and cracking in weldments, turbines, castings, and machined parts.

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