Magnetic Particle Inspection

Abstract

Magnetic particle inspection is a sensitive method of locating surface and some sub-surface defects in ferro-magnetic components. The basic processing parameters depend on relatively simple concepts. In essence, when a ferro-magnetic component is magnetised, magnetic discontinuities that lie in a direction approximately perpendicular to the field direction will result in the formation of a strong ‘leakage field’. This leakage field is present at and above the surface of the magnetised component, and its presence can be visibly detected by the utilisation of finely divided magnetic particles. The application of dry particles or wet particles in a liquid carrier, over the surface of the component, results in a collection of magnetic particles at a discontinuity. The ‘magnetic bridge’ so formed indicates the location, size, and shape of the discontinuity.