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9/8/98 AC 43.13-1B 5-60. GENERAL. Penetrant inspection is used on nonporous metal and nonmetal com- ponents to find material discontinuities that are open to the surface and may not be evident to normal visual inspection. The part must be clean before performing a penetrant inspection. The basic purpose of penetrant inspection is to increase the visible contrast between a discon- tinuity and its background. This is accom- plished by applying a liquid of high penetrat- ing power that enters the surface opening of a discontinuity. Excess penetrant is removed and a developer material is then applied that draws the liquid from the suspected defect to reveal the discontinuity. The visual evidence of the suspected defect can then be seen either by a color contrast in normal visible white light or by fluorescence under black ultraviolet light. (See figure 5-13.) a. The penetrant method does not de- pend upon ferro-magnetism like magnetic par- ticle inspection, and the arrangement of the discontinuities is not a factor. The penetrant method is effective for detecting surface de- fects in nonmagnetic metals and in a variety of nonmetallic materials. Penetrant inspection is also used to inspect items made from ferro- magnetic steels and its sensitivity is generally greater than that of magnetic particle inspec- tion. Penetrant inspection is superior to visual inspection but not as sensitive as other ad- vanced forms of tests for detection of in-service surface cracks. b. The major limitations of the penetrant inspection is that it can detect only those dis- continuities that are open to the surface; some other method must be used for detecting sub- surface defects. Surface roughness or porosity can limit the use of liquid penetrants. Such surfaces can produce excessive background indications and interfere with the inspection. Penetrant inspection can be used on most air- frame parts and assemblies accessible to its application. The basic steps to perform pene- trant inspections are briefly described in the following paragraphs. 5-61. EQUIPMENT USED IN THE PENETRANT INSPECTION PROCESS. Equipment varies from simple aerosol cans used in portable systems to fully automated computer-controlled systems. Whether fluo- rescent or visible penetrants are used, different penetrant bases are available but may require different cleaning methods. Water-washable penetrants can often be removed by a simple water washing process, whereas oil-base penetrants may require special solvents for re- moval. Some oil-base penetrants have emulsi- fiers, either added to the penetrant before it is applied or added afterwards, that allow water washing to be used. Developers used, can be applied either by a wet or dry bath. Therefore, each penetrant inspection process may require different cleaning facilities and procedures. (See table 5-3.) 5-62. BASIC STEPS TO PERFORM PENETRATION INSPECTION. Table 5-4 shows a general process, in the procedures flow sheet, for commonly used penetrant in- spection processes. It is important to ensure that parts are thoroughly cleaned and dried be- fore doing penetrant inspection. All surfaces to be inspected should be free of contaminants, paint, and other coatings that could prevent penetrant from entering discontinuities. Ta- ble 5-5 shows applications of various methods of precleaning for penetrant inspection. Par 5-60 Page 5-29 SECTION 5. PENETRANT INSPECTIONPDF Image | AFS-640
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