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 or a horizontal MPI bench setup. 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. For high sensitivity, a fluorescent liquid and blacklight can be used. This requires a dark testing environment.

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MPI advantages:

  • Rapid inspection of large surfaces
  • Relatively low equipment cost 
  • Detection of surface and subsurface defects
  • Immediate interpretation of indications
  • Can be used in workshop and on site
  • Surface preparation is less critical than with Penetrant Testing (PT)

MPI limitations:

  • Restricted to ferromagnetic materials
  • Requires supply of electricity
  • It is sometimes unclear whether the magnetic field is sufficiently strong to give good indications
  • Cannot be used if thick paint coating is present
  • Some of the paints and particle suspension fluids can cause fire risk, particularly in a confined spaces
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Henk Schroots

Area Sales Manager NDT & Laboratory
+31 (0) 6 49 35 78 02

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