Dye penetrant inspection: Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). Penetrant may be applied to all non-ferrous materials, but for inspection of ferrous components magnetic-particle inspection is preferred for its subsurface detection capability. LPI is used to detect casting and forging defects, cracks, and leaks in new products, and fatigue cracks on in-service components.
1. Section of material with a surface-breaking crack that is not visible to the naked eye.
2. Penetrant is applied to the surface.
3. Excess penetrant is removed.
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Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per centimeter squared is common), along with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant examinations. Inspection of the test surface should take place after a 10 minute development time. This time delay allows the blotting action to occur. The inspector may observe the sample for indication formation when using visible dye. Also of concern, if one waits too long after development the indications may "bleed out" such that interpretation is hindered.
6. Post Cleaning:
The test surface is often cleaned after inspection and recording of defects,especially if post-inspection coating processes are scheduled Features • The flaws are more visible, because: o The defect indication has a high visual contrast (e.g. red dye against a white developer background, or a bright fluorescent indication against a dark background). o The developer draws the penetrant out of the flaw over a wider area than the real flaw, so it looks wider. • Limited training is required for the operator — although experience is quite valuable. • Low testing costs. • Proper cleaning is necessary to assure that surface contaminants have been removed and any defects present are clean and dry. Some cleaning methods have been shown to be detrimental to test sensitivity, so acid