VIDEO
Magnetic Particle Inspection

Here's an excellent video from Karlsruhe University of Applied Sciences
in Germany that clearly explains how magnetic particle tesing works.

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How Magnetic Particle Testing Works

To understand how magnetic particle testing works, we can use the example of a simple bar magnet with a south pole at one end where a magnetic line of force enters, and a north pole at the other, where it exits. If this bar magnet were cracked but not completely broken in half, a north and south pole would develop at the edge of the crack, causing the magnetic field to spread out when it encounters an air gap. When the magnetic field spreads out, it is called a "flux leakage field." Now, if iron particles were sprinkled on this cracked magnet, they would collect not only at the poles at each end, but also at the edges of the crack. This collection of magnetic particles makes it easier to identify the crack in the magnet.

With the magnetic particle testing method, this same principle is applied to ferrous metal parts. After a part is magnetized, it is bathed in a wet flourescent suspension solution that contains iron oxide particles. As with the magnet used in our example, these particles will cluster wherever a flux leakage field occurs - indicating a defect in the surface or near surface of the part. This collection of particles creates an indication of discontinuity which is visible to the trained technician under Ultra Violet (UV) light.

Iron particles cluster around flux leakage field indicating a defect.

MPI uses two different methods of magnetization to assure both horizontal and vertical defects in a part are visible.

Magnetic Particle Inspection Steps →

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