Magnetic Particle Examination is a very effective method for picking up the surface and slightly below the surface discontinuities on material attractive to a magnet. By producing magnetism in the part examined, an inspector can pick up discontinuities such as cracks, porosity, lack of fusion, overlap, etc. open to the surface or slightly below the surface.
Any interruption in the flux or magnetic field in the item under examination can be an indication of a discontinuity. Because the flux field radiates out in a semi-circular pattern from one pole to the other, any transverse break in this field can be detected when an inspector sprays or sprinkles a ferromagnetic powder over the surface. In the event of a break, this powder lines up over the top of the break and can then be detected by visible or black light observation. To ensure that the area has been examined thoroughly, this flux field must be created in two planes.
Magnetic Particle Testing (MT)