Magnetic particle testing is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with iron particles. Surface imperfections distort the magnetic field and concentrate the iron particles near the imperfections. Magnetic particle inspections are typically used to detect cracks, near surface inclusions, seams, laps, and other discontinuities at or near the surface of ferromagnetic materials. Materials that typically fall into this category include carbon steels (<0.8% carbon), low-grade stainless steel and cast iron. It should be noted that magnetic particle inspection can not be used on non-ferromagnetic materials or on parts that have coatings that interfere with the magnetic properties of the material. Magnetic particle inspection can reliably identify surface defects as small as 0.015 inches.

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