Inspection of parts can be expensive Die penatrate is at least a 3 part process. You take a cleaned part soak it clean it and look for penetrate leaching out for a sign of a crack. I believe this is done with a special lite akin to a dark room when you develop photos. I believe that helicopter parts are rated at so many hours and then the dispose and replace of, or inspection of those parts is done. I use chromemoly steel frames and forks. Seat stay cracks and BB cracks several times over the years.