Liquid Dye Penetrant (PT) is one of the most widely utilized non-destructive testing techniques. This technique is primarily used to find surface breaking discontinuities.
When testing a non-ferromagnetic material, the basic premise of Liquid Dye Penetrant Inspection is the use of visible or fluorescent dyed oils, which (through capillary action) work their way into surface breaking discontinuities, only to be blotted out of the indication by a powder.