Magnetic Particle Testing (sometimes called “Mag Particle”) is a process that reveals cracks and similar defects on, or just below, the surface of the casting to about 1/16” deep.
In short, the metal piece, generally steel, is placed in a magnetic field, polarizing each end of the part, creating a north-south pole magnet. If there is a crack in the surface, additional north-south poles are created at the actual crack. This area is known as “magnetic flux leakage” due to the break in the overall magnetization of the part. When a wet suspension of magnetic particles is applied to the part, they are attracted to the cracks and are visibly apparent.