Magnetic particle inspection is used primarily to detect what kind of flaws?

• A. Flaws in the core of the material
• B. Flaws on or near the surface
• C. Deep internal voids
• D. Cosmetic surface irregularities

Answer: (B)

Magnetic particle inspection is most effective for flaws that interrupt the magnetic field at or near the surface of a ferromagnetic part. When the part is magnetized and fine iron particles are applied, they gather at points where the magnetic flux leaks out due to a defect. This makes surface-breaking cracks, seams, laps, or other near-surface discontinuities visible as distinct indications on the surface. Deep internal voids don’t produce the same surface leakage unless they reach or are very close to the surface, so they’re not reliably detected by this method. Cosmetic surface irregularities don’t inherently create the kind of flux leakage patterns MPI looks for, so the technique focuses on flaws on or just beneath the surface.