Magnetic Particle Inspections

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 MPI 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 v.s. Dry Magnetic Media Application

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

Advantages of MPI

  • 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.