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It is crucial to test any machine or material consisting metal in order to prevent major discontinuities.

Magnetic Particle Inspection (MPI) is a nondestructive testing process that detects discontinuities (seams, laps, grinding and quenching cracks) on surfaces and subsurfaces of iron, nickel, cobalt, their alloys and other ferromagnetic materials.

How does it work?

A magnetic field is put into the ferromagnetic part and is magnetized by direct or indirect magnetization. If the ferromagnetic part has a discontinuity, then it will interrupt the magnetic field flow and a leakage field will occur. An application called magnetic media is then used to coat the part and form a mark over the discontinuity. The mark can only be visible under proper lighting conditions.


Wet More sensitive since it gives the magnetic particles more mobility because it is a liquid. There are two types of wet particles: One is visible and can be viewed under normal white light while the other is fluorescent and can only be viewed under black light.

Dry More of a dust that is light and more portable. It comes in a variety of colors so that a color can be chosen that produces a high level of contrast against the background of the ferromagnetic part


  • Detects both surface and subsurface defects
  • Inspects parts with unusual shapes
  • Pre-cleaning is easy and not as critical as other inspection methods
  • Fast and cheaper than other methods
  • Very portable

If you use ferromagnetic materials make sure to contact CODE STEEL to come and inspect it with the MPI test before it’s too late.