What Is Magnetic Particle Testing?

Magnetic particle testing, sometimes called an MT process, is a nondestructive means for detecting a discontinuity in a ferromagnetic material. In other words, it tests certain elements for their ability to attract to a magnet.

Elements Tested

Iron, nickel, cobalt and some of the rare earth metals such as gadolinium or dysprosium have ferromagnetic qualities. Visually, these can be found at the center of the periodic table of the elements, in groups 3 to 12. They are also referred to as alloys.

Identifying the Discontinuity

Provided the testing metal is accurate, the particles are colored and coated with dyes that are made visible with a hand-held ultraviolet light. During magnetization with a direct current or with an electromagnet, the magnetic particles are attracted by the surface field in the area of the defect. The particles then hold on to the edges of the defect, so it looks like a build-up. The technician knows this build-up to be where the error in the testing object is located.

Misconception

This method is suitable only for metallic materials, which can be intensely magnetized. Some testing labs try to use MT methods for metals like aluminum, which cannot be magnetized.

Time Frame

A typical MT takes no less than six hours, and no more than eight, according to Stephens.

Significance

MT is used primarily in steel factories and can sometimes be done in radiology labs.

References

• Magnetic Particle Inspection; MJ Lovejoy; 1993
• Mr. John Stevens; PCA Engineering; Pompton Lakes, NJ