Which NDT method uses conductive materials to detect surface and subsurface flaws?

• A. ET (Eddy Current Testing)
• B. MT (Magnetic Testing)
• C. UT (Ultrasonic Testing)
• D. VT (Visual and Dimensional Testing)

Answer: (A)

Eddy current inspection uses electromagnetic induction in conductive materials to reveal flaws. An alternating current in a probe creates a magnetic field that induces eddy currents in the test piece. Any flaw, such as a crack or thinning, disturbs the eddy current flow, causing a change in the coil’s impedance that the probe detects. The currents are concentrated near the surface, so surface and near-surface defects are especially detectable. Because this method relies on electrical conductivity, it works only on conductive materials. Other methods rely on different physical principles—magnetic testing uses flux leakage in ferromagnetic materials, ultrasonic testing uses sound waves to image internal features, and visual/dimensional inspection looks at the surface directly—so they don’t match the same capability for conductive materials detecting surface and subsurface flaws.