Magnetic particle inspection (MPI) is a process for detecting surface and shallow subsurface discontinuities (approx. 6mm deep) in ferromagnetic materials.
It is based on the principle of magnetic induction. The tested part is magnetized. Finely crushed ferrous particles coated with colored pigment are applied on the tested surface.
Attracted by the action of the magnetic flux of discontinuity, the particles are accumulated and form an indication directly above discontinuity. This indication is remarkably visible under appropriate light conditions.
This quality testing method is cheap and quick but limited given with the non-ferromagnetic materials, discontinuities deep beneath the surface, and the impossibility of determining the depth of the crack which was discovered in ferromagnetic materials.
