Dye penetrant testing is primarily used to detect which type of defect?

• A. Surface defects
• B. Internal defects
• C. Magnetic anomalies
• D. Subsurface porosity

Answer: (B)

Dye penetrant testing reveals flaws that break the surface. The method uses a dye that seeps into openings on the surface of a material, such as cracks, seams, laps, or porosity that connects with the surface. After removing the excess dye and applying a developer, the trapped dye is drawn out along these surface-connected openings, creating visible indications that pinpoint where the surface itself is defective. Because the technique relies on the dye entering and exiting through surface openings, it isn’t effective for defects entirely buried inside the material that do not communicate with the surface. This is why dye penetrant testing is best for surface defects rather than internal or subsurface anomalies, magnetic-related issues, or porosity that isn’t open to the surface.