Fluorescent Penetrant Inspection (FPI) in Practice
Fluorescent penetrant inspection(FPI), or penetrant testing (PT), is also the crucial one of methods of non-destructive testing(NDT) used in the aerospace industry, which is also the one of the oldest approaches to detect surface flaws like cracks, porosity, gouges, and seams on non-ferrous and also non-porous materials metals, plastics, ceramics and glass, inspectors add the fluoresent dye penetrant to target areas on a surface of the safety parts and critical components, which the defects propagate once a critical size is reached, they would be caused catastrophic part failure.
By capillary action, the fluorescent dye penetrant penetrates into the openings and coating the flawed areas of part-to-be-inspected. After the fluorescent penetrant excess dye is removed, an additive called the “developer” is introduced, and it draws the remaining fluorescent penetrant out. After a final cleaning step, the fluorescent penetrant that penetrated through the developer exposes the critical cracks and porosity in part when viewed under a UV LED lamp / black light.
In the process, it uses a fluorescent dye penetrant that will fluoresce under UV LED lamp/black light, and the fluorescent dye penetrant becomes ‘stuck’ in the surface indications on the surface of the part after processing according to ASTM E165, ASTM 1417 and ASTM E3022.
While FPI and PT both can be used in nearly any NDT application, compatibility of test materials must be considered for the specific industry. With the inherent severity of chemical incompatibility in the aerospace industry, manufacturers developed classes of penetrants best suited for that industry. The most common penetrant systems in aerospace are Type I (fluorescent), Methods A, B, and D (water washable, post emulsified – lipophilic, and post emulsified – hydrophilic, respectively).