Magnetic particle inspection is a method that can be used to find surface and near surface flaws in ferromagnetic materials such as steel and iron. The technique uses the principle that magnetic lines of force (flux) will be distorted by the presence of a flaw in a manner that will reveal it's presence. The flaw (for example, a crack) is located from the "flux leakage", following the application of fine iron particles, to the area under examination. There are variations in the way the magnetic field is applied. But they are all dependant on the above principle.

The iron particles can be applied dry or wet; suspended in a liquid, coloured or fluorescent. While magnetic particle inspection is primarily used to find surface breaking flaws, it can also be used to locate sub-surface flaws. But it's effectiveness quickly diminishes depending on the flaw depth and type.

Surface irregularities and scratches can give misleading indications. Therefore it is necessary to ensure careful preparation of the surface before magnetic particle testing is undertaken.

Crack on roll surface.

Cracks on roll surface.