Which NDT method uses dye and developer to indicate imperfections?

• A. PT (Liquid Penetrant Testing)
• B. VT (Visual and Dimensional Testing)
• C. ET (Eddy Current Testing)
• D. MT (Magnetic Testing)

Answer: (A)

Liquid penetrant testing uses a dye-based penetrant that enters any surface-breaking flaw by capillary action. After applying the penetrant and letting it dwell, the surface is cleaned and a developer is applied. The developer draws the penetrant out of the defect and concentrates it at the surface, creating a visible (or fluorescent) indication that reveals the flaw under proper lighting. This method is especially good for spotting small cracks, laps, or porosity on accessible surfaces. It’s different from methods that rely on visual inspection alone, electrical or magnetic responses, because those do not use dye and developer to highlight surface flaws.