Magnetic particle inspection

Principle of magnetic particle inspection

Magnetic particle inspection is a non-destructive Material testing method. It is also referred to as the magnetic particle method of crack detection, magnaflux testing or magnafluxing. This method can be used to detect cracks on or close to the surface of ferromagnetic materials.

The workpiece or part of it is first magnetised by passing a current through it. In the case of direct magnetisation, an annular magnetic field is generated. In the case of indirect magnetisation, a magnetic field is created along the component. A combination of the two is possible.

The magnetic field lines run parallel to the surface. Cracks or defects produce a magnetic leakage field that can be made visible using fluorescent ferromagnetic powders dispersed in suitable liquids. UVA or blue light sources are normally used for this purpose.

This method is only suitable for defects that are close to or extend as far as the surface. Defects running parallel to the surface (e.g. material separations) cannot be detected.