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Inspecting for Cracks The existence or full extent of cracks in major structural members cannot be accurately determined by a visual inspection; therefore, several methods other than visual are used. They are ultrasonic waves, X rays, Zy-glo, and a penetrating dye. When using ultrasonic waves, only one side of the inspected metal need be accessible. With X-ray equipment both sides of the metal must be accessible. The Zy-glo method requires blacklight equipment. Penetrating dye requires no complex or expensive equipment, and it can be easily used in the field. The materials to make a dye-penetrant inspection consist of the penetrating dye, dye remover, and dye developer, all contained in an inspection kit. Individual items for the kit can be requisitioned to replace those which have been used. The paragraphs that follow describe how the kit is used. Preparation. All coats of paint and surface dirt must be removed before the dye penetrant is applied. A thoroughly clean surface is required to ensure an accurate portrayal of the structural member's condition. Application. The surface to be inspected is given a final cleaning by applying dye remover and wiping the surface with clean cloths. Then a coat of dye penetrant is applied by brushing or swabbing and allowed to penetrate for 3 to 15 minutes. Removal. The dye penetrant on the surface is removed by wiping the excess off, first with a dry cloth and then with a cloth moistened with dye remover. If a water rinse is used, the inspected part must be thoroughly dried before applying the dye developer. Development. A light, even coating of dye developer is applied with a brush or by spraying. Whichever method is used, be sure that the coating is free of runs or laps. The developer dries and forms a smooth, white coating. Cracks show up as red lines, and the extent is indicated by the length of the red lines. Narrow or tight cracks show up as a series of red dots close together. Scattered dots that do not show a pattern indicate porousness. Because this method is so sensitive, evaluating the indicated cracks requires good judgment. After the flaws have been detected and marked, remove the developer with dye remover or an approved petroleum solvent. Warning Dye-penetrant materials are flammable, particularly the developer. They must be used only in well-ventilated areas away from sparks or flames. The fumes must not be breathed for prolonged periods; and gloves, goggles, and aprons are recommended for protection. Contaminated skin must be washed with soap and water, and contaminated clothing must be changed at once and laundered before reuse.
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