Magnetic particle inspection

Magnetic Particle Inspection (MPI) also sometimes called as Magnetic Test (MT) is a non-destructive test method for the detection of surface and sub-surface discontinuities in ferrous materials.

The first step in a magnetic particle inspection is to magnetize the component that is to be inspected. If any defects on or near the surface are present, the defects will create a leakage field. After the component has been magnetized, iron particles, either in a dry or wet suspended form, are applied to the surface of the magnetized part. The particles will be attracted and cluster at the flux leakage fields, thus forming a visible indication that the inspector can detect. The particles are often colored and usually coated with fluorescent dyes that are made visible with a hand-held ultraviolet (UV) light (black light). The test method using fluorescent coated particles is called as Fluorescent Magnetic Particle Inspection or test (FMPI) and the usage of other coloured particles is termed as colour contrast Magnetic Particle Inspection or test (MPI).