The Magnetic Testing method (MT), aimed to highlight surface and sub-surface cracks, is realized by magnetizing the piece’s surface and spraying a magnetic particle liquid on the area that has to be inspected. In case of discontinuities, a magnetic flux “leakage” appears on the surface in correspondence with the discontinuity itself. The generated magnetic flux can attract fine-grained magnetic particles in order to get visible the indications.

The control technique is very sensitive and can detect defects even on parts covered with thin protective layers (for example paints), although with a slight decrease in sensitivity. The detection of the defects can be carried out using magnetic particles applied dry or by means of a suspension in a suitable liquid agent. The particles can be coloured to be visible in white light or fluorescent in Wood’s light (UV radiation). The fluorescent magnetic particles inspection technique reaches higher sensitivity.