![]() ![]() The removal method is controlled by the type of penetrant used. The excess penetrant is then removed from the surface. Due to their incompatible nature one must be careful not to apply solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant. As expected, smaller flaws require a longer penetration time. The dwell time mainly depends upon the penetrant being used, material being tested and the size of flaws sought. The penetrant is allowed "dwell time" to soak into any flaws (generally 5 to 30 minutes). The penetrant is then applied to the surface of the item being tested. Note that if media blasting is used, it may "work over" small discontinuities in the part, and an etching bath is recommended as a post-blasting treatment. The end goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination. ![]() ![]() Cleaning methods may include solvents, alkaline cleaning steps, vapor °reasing, or media blasting. The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Stationary systems with dedicated application, wash, and development stations, are more costly and complicated, but result in better sensitivity and higher samples through-put. This technique can be quite portable, because in its simplest form the inspection requires only 3 aerosol spray cans, some lint free cloths, and adequate visible light. One must also assure that the test chemicals are compatible with the sample so that the examination will not cause permanent staining, or degradiation. When selecting a sensitivity level one must consider many factors, including the environment under which the test will be performed, the surface finish of the specimen, and the size of defects sought. Since Fluorescent penetrant inspection is performed in a darkened environment, and the excited dyes emit brilliant yellow-green light that contrasts strongly against the dark background, this material is more sensitive to defects. Fluorescent penetrants contain two or more dyes that fluoresce when excited by ultraviolet (UV-A) radiation (also known as black light). Visible penetrants are typically red in color, and represent the lowest sensitivity. Penetrants are classified into sensitivity levels. Inspection is performed under ultraviolet or white light, depending upon the type of dye used - fluorescent or nonfluorescent (visible). The developer helps to draw penetrant out of the flaw where an invisible indication becomes visible to the inspector. After adequate penetration time has been allowed, the excess penetrant is removed, a developer is applied. Penetrant may be applied to the test component by dipping, spraying, or brushing. Liquid penetrant inspection is used to detect any surface-connected discontinuities such as cracks from fatigue, quenching, and grinding, as well as fractures, porosity, incomplete fusion, and flaws in joints.ĭPI is based upon capillary action, where low surface tension fluid penetrates into clean and dry surface-breaking discontinuities. Dye Penetrant Inspection What is Dye Penetrant Inspection?ĭye Penetrant Inspection (DPI), also called Liquid Penetrant Inspection (LPI) or Penetrant Testing (PT), is one of the oldest and simplists NDT methods where its earliest versions (using kerosene and oil mixture) dates back to the 19th century. ![]()
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