Magnetic particle testing is one of the very common NDT methods. The main application is in the automotive and aerospace industry, and also in energetics and transportation industry. Due to simple physical background this method is easy to perform and it is very often required during the maintenance of the plant. MT is able to detect the surface and sub-surface imperfections (cracks, porosity, inclusions etc.) in the ferromagnetic (Fe) material. For other materials (non-ferromagnetic) MT is not applicable.

Physical background

The ferromagnetic material becomes magnetically saturated if it is magnetized in a proper way. The material discontinuity has different magnetic properties (usually is non-magnetic - air inside of the crack, slug or gas in porosity). This inhomogeneity of the magnetic properties deforms magnetic field, its force lines step off the material to surface, and create the scatter magnetic flow. This flow holds the information about magnetic inhomogenity. The magnetic powder is applied on the surface of the material. This powder is in place of the material magnetic properties fitted to the surface by the scattered magnetic flow. This fitted cluster of magnetic powder creates an indication. The indications have bright or color contrast and could be easily seen on the background material. The MT is able to detect the imperfections from width of a few microns.