Dye Penetrant or Liquid Penetrant Testing (DP/LPT) is a Testing that can be carried out on ferrous and non-ferrous components (essentially non-porous) and welds by Water Washable Processes, Visible and Fluorescent Penetrant Systems. It is generally carried out on the surface.
Penetrant testing is one step up from visual inspection and offers many advantages, such as speed, large-area coverage, and cheapness.
It is usually a six-stage process:
- surface cleaning (degreasing etc)
- application of a penetrant liquid (dipping, spray, brush)
- removal of excess penetrant (solvent, water)
- application of developer
- inspection of test surface (visual, television camera)
- post-inspection cleaning (anti-corrosion solutions).
There are three major groups of penetrant processes:
- water-soluble
- post-emulsifiable with water rinsing
- solvent removable, the difference being in the method used to remove the excess penetrant.
In each of these three groups, the penetrant solution can contain a dye to make the indication visible under white light, or a fluorescent material which fluoresces under suitable ultraviolet (UV-A) light.
