Various types of liquid penetrant testing (PT) methods are utilized to detect material defects open to the surface or to detect open surface cracks. Red dye or fluorescent penetrants are utilized as well as various types of wet and dry developers. Fluorescent dye penetrant examinations are performed under black light conditions to ensure the highest detectability for very fine fatigue cracks.
Penetrant solution is applied to the surface of a pre-cleaned component. The liquid is pulled into surface-breaking defects by capillary action. Excess penetrant material is carefully cleaned from the surface. A developer is applied to pull the trapped penetrant back to the surface where it is spread out and forms an indication. The indication is much easier to see than the actual defect.