MAGNETIC PARTICLE TESTING (MT) IS AN NDT INSPECTION TECHNIQUE that uses magnetism and its principles to find cracks, also known as flux leakage sites, in metals.

Photo credit: @grubn_roht

Using direct or indirect magnetism, MT can detect surface and shallow subsurface discontinuities in steels as well as their alloys. 
In order for a material to hold a magnetic field after the passing of electric current, the material must contain nickel, cobalt, and/or iron. Therefore, this technique is not valid where none of these elements are present, such as in: 

• Aluminum

• Inconel

• Composite