Penetrant Test (PT) is a sensitive method of detecting minute discontinuities that are open to the surface of the weld.

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.  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. fluorescent penetrant test requires an ultraviolet light (black light) to observe the test results. It may be necessary to enclose the viewing area in order to properly read the test results.