What Is Liquid Penetrant Testing?
Liquid Penetrant Testing (PT) — also referred to as Dye Penetrant Inspection (DPI) or Liquid
Penetrant Inspection (LPI) — is an NDT method that uses the capillary action of a liquid
penetrant to detect surface-breaking discontinuities in solid, non-porous materials. The
penetrant is applied to the cleaned component surface, allowed to dwell, removed from the
surface, and followed by a developer application that draws the entrapped penetrant back out of
any surface-breaking discontinuity — producing a visible indication that reveals the location,
orientation, and approximate extent of the defect.
PT Methods Available:
- Type I — Fluorescent Penetrant — Fluorescent dye examined under UV-A illumination;
higher sensitivity; required for many aerospace and energy applications
- Type II — Visible Dye Penetrant — Red dye examined under white light; simpler field
application; suitable for general industrial inspection
- Method A — Water-Washable — Suitable for components with rough surfaces or large
quantities
- Method B — Post-Emulsifiable (Lipophilic) — Higher sensitivity; requires emulsifier
application before washing
- Method C — Solvent-Removable — Portable, self-contained application; widely used for
f
ield spot inspection
- Method D — Post-Emulsifiable (Hydrophilic) — Highest sensitivity; required for critical
aerospace and energy applications