Finding surface defects in ferromagnetic metals
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 portable yoke or a horizontal MPI bench setup. Defects in the surface and shallow subsurface cause magnetic field fluxes to "leak". When a liquid containing small 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 black light can be used. This requires a dark test environment.
MPI advantages:
- Fast inspection of large areas
- Relatively low equipment costs< br /> - Detection of surface and subsurface defects
- Immediate interpretation of indications
MPI limitations:
- Restricted to ferromagnetic materials
- Cannot be used as there is a thick layer of paint
