Which NDT method is particularly suited to detect near-surface defects in ferrous materials?

• A. Ultrasonic method
• B. Magnetic particle inspection
• C. Radiographic method
• D. Dye penetrant method

Answer: (B)

Magnetic particle inspection works best here because ferrous metals can be magnetized, and any defect near the surface disrupts the magnetic flux, causing leakage that attracts magnetic particles. This makes near-surface and surface-breaking flaws highly visible as particle accumulations on the surface, which is exactly what MPI is designed to reveal. Ultrasonic testing can find internal features and requires good coupling and can be less sensitive to very small near-surface flaws in rough ferrous surfaces. Radiography shows density differences inside the part and is not specifically optimized for near-surface flaws. Dye penetrant detects surface-breaking cracks but mostly reveals flaws that open to the surface, not those just beneath it.