The developer acts as blotter, drawing trapped penetrant out of imperfections open to the surface. With fluorescent dyes, ultraviolet light is used to make the bleedout fluoresce brightly, thus allowing imperfections to be readily seen. Surface and near-surface imperfections distort the magnetic field and concentrate iron particles near imperfections, previewing a visual indication of the flaw. Radiography involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. An X-ray generator or radioactive isotope is used as a source of radiation.
Radiation is directed through a part and onto film or other imaging media.
The resulting shadowgraph shows the dimensional an features of the part. Possible imperfections are indicated as density changes on the film in the same manner as a medical X-ray shows broken bones. As in ultrasonic testing, acoustic emissions can be detected by special receivers. Emission sources can be evaluated through the study of their intensity, rate and location. Several techniques are used to detect and locate leaks in pressure containment parts, pressure vessels, and structures.