Liquid Penetrant Testing (LPT), also called Dye Penetrant Inspection (DPI) and Penetrant Testing (PT), is widely used to detect surface defects in castings, forging, welding, material cracks, porosities and possible fatigue failure areas.

The material is cleaned and then coated with a visible or fluorescent dye solution.  Technicians remove the excess solution after waiting a specified time (Dwell Time) than he/she applies a developer to the material. The developer acts like a blotter, pulling the dye solutions out of the imperfections. Visible dyes will show a sharp contrast between penetrant and developer making the “bleedout” easy to see. Fluorescent dyes are viewed with an ultraviolet lamp, which makes the “bleedout” fluoresce brightly reveling any material imperfections.