Which NDT technique uses magnetic fields to detect defects in ferromagnetic materials?

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

Answer: (A)

The main concept tested is recognizing which nondestructive method uses magnetic fields to find flaws in ferromagnetic materials. Magnetic Testing works by magnetizing the part and then looking for leakage fields at discontinuities such as cracks or gaps. When a defect disrupts the magnetic circuit, flux leaks to the surface or near-surface region, creating indicators that can be seen with magnetic particles or detected by flux-leakage sensors. This approach is especially effective for ferromagnetic metals like steel because their magnetic properties cause defects to disturb the magnetic field in a detectable way. The other methods rely on different physical principles—visual inspection uses sight, ultrasonic testing uses sound waves, and eddy current testing relies on induced currents—so they don’t introduce magnetization and flux leakage as the primary defect-detection mechanism in ferromagnetic materials.