Magnetic Particle Testing Procedure ISO 17638 & Acceptance Criteriya ISO 23278.
MPT is a nondestructive testing method for locating surface and near surface discontinuities in ferromagnetic materials. It depends for its operation on the fact that when the material or part under test is magnetized, discontinuities that lie in a cause leakage field to the direction of the magnetic field will cause a leakage field to be formed at and above the surface of the part. The presence of this leakage field, and therefore the presence of the discontinuity, is detected by the use of finely divided ferromagnetic particle applied over the surface, some of the particle being gathered and held by the leakage field.
Ferromagnetic materials include most of the iron, nickel and cobalt alloys. These materials lose their ferromagnetic properties above a characteristic temperature called the Curie point which is approximately 760◦ C for most of the ferromagnetic material.