The magnetic type of nondestructive testing is used mainly for testing items of ferromagnetic materials, i.e. materials which are capable of essentially changing their magnetic characteristics under the effect of an external (magnetizing) magnetic field. Operation of magnetization (placement of item into the magnetic field) is a must in this type of testing. Data or information retrieval may be performed from the full cross-section of the sample (item) or from its surface.

MPI is used to detect surface-breaking and near-surface flaws in ferromagnetic materials. It cannot, however, be used to detect deeply embedded flaws, nor can it be used on non-ferromagnetic materials, such as aluminium, copper or austenitic stainless steel.

The Benefits of MPI inspection is generally simple to operate and apply. Can inspect parts with irregular shapes easily. Precleaning of components is not as critical as it is for some other inspection methods. Most contaminants within a flaw will not hinder flaw detectability. The test is visual, so any indications can be seen and recorded (i.e. Photos).

Very fast and effective to test large areas for minor defects. Considered low cost compared to many other NDT methods. It Is a very portable inspection method especially when used with battery powered equipment.