Magnetic Particle Inspection (MPI) is a process used in ferromagnetic materials (Iron, Steel, Nickel and Cobalt).

In a nutshell, the process involves spraying the welded material with a white paint aerosol, then spraying the black whilst running an electromagnetic current over the weld using an electromagnetic yoke which draws the ink to the crack, which gives a good indication of the size and shape of a crack in the material.

Items related to this area include (among others): Electromagnetic Yoke, Permanent Magnets, White Contrast Paint & Black Magnetic Ink.