Liquid Penetrant Inspection (PT), or dye penetrant inspection, is used to find surface connected discontinuities on non-porous materials.
PT can be performed on any non-porous material but MT is often the preferred test method on ferromagnetic materials when looking for cracks. PT uses a low surface tension fluid with a contrasting dye to penetrate into surface discontinuities. The liquid penetrant dye is cleaned off the surface of the part. A developer is then applied to the part drawing out the dye from the surface connected discontinuities.
Liquid penetrant comes in several types and methods:
- A. Water Washable
- B. Post-emulsifiable - lipophilic
- C. Solvent Removable
- D. Post-emulsifiable - hydrophilic
- 1. Fluorescent
- 2. Visible
In addition, developer comes in several different forms. Dry powder, water soluble, water suspendable, and non-aqueous.
The surface of the part being inspected must be free of any coatings. Cleanliness of the part is also an important factor to the quality of the inspection.