Magnetic particle inspection (MPI)

Magnetic Particle Inspection (MPI) or Magnetic Testing (MT) is an NDT method for checking the surface integrity of ferromagnetic materials. The material is magnetized using a handheld yoke. Defects in the surface and shallow subsurface cause magnetic field fluxes to "leak". When a liquid containing tiny magnetic particles is applied, these particles accumulate around those discontinuities making them visible to the naked eye. If necessary a white contrast agent is applied to the material before testing.

Magentic particle inspection

  • Low cost

  • Portable equipment (if any)

  • Immediate results

  • Minimum special skills required

  • Minimum part preparation

Advantages of MPI

  • Only suitable for surfaces than can be viewed

  • Usually only larger defects can be detected

  • Scratches can be misinterpreted for cracks

  • Quality of inspection influenced by surface condition, physical conditions, environmental factors and physiological factors

Limitations of MPI