Magnetic Particle Testing
Magnetic particle testing is a method for detecting cracks and other discontinuities on surface and subsurface of ferro-magnetic materials. Sensitivity of detection is maximum at the surface and diminishes rapidly with increasing depth of sub-surface defects. Detection of defects depend on the fact that when a material is magnetized, discontinuities which lie transverse to the direction of magnetization cause distortion of the magnetic lines of flux and a leakage field is formed at or above the surface, some of these particles are held by the leakage flux.
These magnetically held collection of particles form outline of effects and show location, shape and extent of the discontinuities. A number of factors such as direction and strength of the magnetic field, magnetic character of the part, location and orientation of discontinuities and type of the magnetic powder applied, affect the formation of the powder pattern, and therefore exact location of the flaw is indicated by the method.