Magnetic particle examination is widely used on ferromagnetic parts on edge preparations of welds and on the welds before and after the vessel has been subjected to hydrostatic test.

Magnetisation is done by passing current through copper electrodes and sometimes by a hand held electro-magnetic yoke. This technique is best employed for both detecting surface discontinuities that may lie below surfaces.

When a part of area is magnetized, magnetic lines of force or magnetic flux will be developed. If a medium such as iron-powder is dusted on the surface of the part during magnetization, any discontinuity which interrupts the lines of force more or less in perpendicular direction will set – up flux leakage at the surface and there by attracting the powder to fotm a build–up resembling the discontinuity. All linear discontinuities