LPI is used to reveal which type of discontinuities?

• A. surface breaking discontinuities
• B. internal voids
• C. subsurface inclusions
• D. dimensional irregularities

Answer: (A)

Liquid Penetrant Inspection reveals surface-breaking discontinuities. The technique works because penetrant liquid is drawn into flaws that have a path to the surface. After excess penetrant is removed, a developer is applied and pulls penetrant out of the flaw, producing a visible indication on the surface (colored or fluorescent). Since the liquid must reach the flaw from the surface, defects that are completely internal and do not communicate with the surface won’t be reliably detected. Subsurface inclusions or internal voids not connected to the surface aren’t revealed by this method, and dimensional irregularities aren’t the type of discontinuities LPI is designed to show.