Magnetic particle inspection is most effective in detecting what type of defects?

• A. Cracks, porosity, inclusions, and voids at or near the surface in ferrous materials
• B. Surface discoloration
• C. Temperature changes
• D. Elastic deformation under load

Answer: (A)

Magnetic particle inspection works by magnetizing a ferrous part and looking for leakage fields that appear where the magnetic flux is interrupted by a flaw. Those leakage fields attract magnetic particles, forming visible indications that outline the defect. This makes the method especially effective for finding cracks, porosity, inclusions, and voids that are at or near the surface in ferrous materials, where the disturbance to the magnetic circuit is strongest and easiest to reveal with particles.

Surface discoloration isn’t a defect in the material’s magnetic path, so it won’t reliably show up with MPI. Temperature changes aren’t detected by this method, and elastic deformation under load is a mechanical change that doesn’t necessarily create the kind of discontinuity MPI looks for.