What is Magnetic Particle Inspection and How Does it Work?

May 24, 2021

Magnetic Particle Inspection: How does it work?

Magnetic Particle inspection is a commonly used nondestructive testing method for finding cracks and other surface level flaws in iron, steel, and other ferromagnetic material. Most people know of magnetic particle inspection, but not has stopped to ask, how exactly does it work?

As the name implies, magnetic particle inspection works through the principle of magnetism and as such the tested material must first be magnetized before testing can commence. This is done to induce a magnetic field in the inspection piece. Because metals can support a more magnetic flux (per unit volume) cracks or discontinuities in the inspection piece cause distortions and leakage of the magnetic flux.

The consumables that are required for magnetic particle inspection contain ferromagnetic particles, these particles are drawn to the flux leakage fields and build up around the excess flux indicating discontinuities in the material.

Not every indication found in the test piece is necessarily a problem, things like fine thread, scratches, keyways, or other discontinuities can create flux leakage and cracking indications. Skilled testing personnel are of paramount importance when it comes to appropriately interpreting MPI results and deciding whether accept or reject the inspection piece.

Rapallo has a team of highly skilled NDT technicians that have decades of experience interpreting the results of MPI, and other NDT methods, contact us for further information on the science behind MPI or to get a quote on any of our NDT services.




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