Copyright Goodheart-Willcox Co., Inc. 268 Gas Tungsten Arc Welding Handbook A penetrant test is particularly useful on nonmagnetic materials, where a magnetic particle test cannot be used. Penetrant tests are used extensively for exposing surface defects in welds on aluminum, titanium, magnesium, and austenitic stainless steel weldments. Figure 18-5 shows how penetrant inspec- tion can also be used to detect leaks in both open-top and sealed tanks or vessels. The penetrant is sprayed around all the weld areas. Penetrant works by capil- lary action and will identify any weld discontinui- ties or defects. When testing a sealed tank, the dye is sprayed (or brushed) on the external sides of the welds. The two types of penetrant tests are dye pene- trant and fl uorescent penetrant. A dye penetrant test requires the surface of the weld to be sprayed generously with penetrant and allowed to soak for a specifi ed time. Excessive pene- trant is removed with an aerosol cleaner. All of the penetrant is then wiped from the weld area. After the penetrant is removed, the developer is applied. The developer is a powdery white substance that is lightly applied from an aerosol can. Any imperfections in the weld will hold the dye and bleed through the white developer, identifying the problem. A dye penetrant test can be done anywhere because it is portable, and it can be done in any position. The results can be detected in normal light, without the use of special equipment. A B C D Figure 18-4. Dye penetrant test sequence. A—The penetrant is applied to the weldment. B—The penetrant is cleaned off the weldment. C—The developer is applied to the weldment. D—The weldment is inspected for discontinuities that appeared after the developer was applied. (Mark Prosser)