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.
Rapid inspection of large surfaces
Relatively low equipment cost
Detection of surface and near-surface defects
Immediate interpretation of indications
Can be used in workshop and on site
Surface preparation is less critical than with Penetrant Testing (PT)
This method is typically ‘colour-contrast’ with white contrast paint and black ink. However, for high sensitivity, a fluorescent ink and blacklight can be used. This requires a dark testing environment.