Magnetic Particle Inspection (MPI) is a Method for detecting surface and sub surface discontinuities in ferromagnetic materials such as iron,nickle,cobalt and some of their alloys.This method is working on the base of passing the magnetic field into the testing parts.
Magnetic Particle Examination is accomplished by inducing a magnetic field into a ferromagnetic material and applying iron particles to the surface of the item being examined. Surface and near-surface discontinuities affect the flow of the magnetic field within the part causing the applied particles to gather at locations of flux leakage, thus producing a visible indication of the irregularity on the surface of the material.