What is Magnetic Particle Inspection

Magnetic Particle Inspection (MPI) is a method of non-destructive testing (NDT) that indicates the presence of surface and near-surface imperfections in materials that can be magnetized.

The surface of the component is cleaned, to insure the component is free of impurities that may bond to the surface, making it appear to be flawless, i.e. lubricant oils, paint, wax. Next, the component is measured for residual magnetism, followed by a strong electromagnetic field that is induced into the part. When the magnetic field comes upon a flaw in the component, the magnetic field will “flare” creating a much stronger magnetic field. Metallic particles (iron filings) are applied over the component (the particles can be either dry or wet) and be visible in white light or florescent under black light. The magnetic particles collect at the points where the magnetic field has been broken by the surface or near-surface indications. The component is then inspected visually to identify the indications size and orientation. The final step is to demagnetize the component. This is accomplished by changing the direction of the magnetic field and measuring the component to ensure that there is no residual magnetism left in the component.