PT is commonly performed on aluminum. Penetrants due not have a resolution, they have sensitivity levels with the sensitivity increasing with the rating (i.e.:a penetrant with a rating of 4 is much greater than that with a sensitivity of 1). The sensitivity refers to it's ability to migrate into finer or tighter cracks or other discontinuities open to the surface.
It is a very practical test method when performed properly, that is why most do not care for it, typically I see this method performed incorrectly, very common. I did not imply anyone has performed the test incorrectly posting replies, only that discontinuites will not be discovered when it is performed or interpreted incorrectly.
I found major IJP/IF on one Al job a couple of years ago - how? The rate and quantity of the pentrant being drawn by the developer is a good indicator. While the opening(s) on the surface were quite small (barely visible even with a 3X magnifier), I knew there were large voids in the interior of the weld - from the weld surface. It is an aquired skill, just like welding (or spelling). My findings were dismissed and a UT tech was called out. He concurred with my findings and excavations were performed verifying the PT results.
The residue left behind by developer, penetrant or cleaner is indicitive of improper cleaning, thereby resulting in contamination of the weld by these materials. Many aerospace/aircraft parts are tested using this method, the next time you board a plane, most of the rotating parts are PT in addition to RT, UT or ET (as well as other exotic test methods depending on the part.) Consider that fact during take off.
Most of my post has been factual as witnessed by myself, or one of my Level II or Level III buddies. Cleaning penetrant of with remover, simply wiping developer off with a dirty rag or paper towels with much lint, improper dwell or developing times often contribute to welding problems.
I have taken several (Al) tests when I worked aerospace where root, intermediate and cover passes had PT performed - passed radiography later. It was a contractual requirement for the welding engineer to perform these tests.
Personally, I don't think PT is better than VT, or vice versa, it all depends on the application, material, and experience of the inspector and technician. As far as test or inspection, the semantics of these terms have been hit on in the Forum in the past, either way - test/inspection/evaluation/examination, competance and experience are usually the determining factors.
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