Magnetic Particle Inspection: MPI

The most common / widely used method of NDE is magnetic particle inspection which uses finely divided iron or magnetic iron oxide particles, held in suspension in a suitable liquid (often kerosene). This fluid is referred to as the carrier. The particles are often colored and can be coated with fluorescent dyes that are made visible with a hand-held ultraviolet (UV) light. The suspension is sprayed or painted over the magnetized specimen during magnetization which is provided by a direct current or with an electromagnet, to localize areas where the magnetic field has protruded from the surface. The magnetic particles are attracted by the surface field in the area of the defect and hold on to the edges of the defect to reveal it as a build up of particles.