What is Magnetic Particle Inspection

Magnetic Particle Inspection (MPI), also known as Magnetic Testing (MT), is one of the most commonly used non-destructive testing methods for detecting surface and shallow sub-surface defects in welds, castings and forged ferromagnetic materials including steel, cobalt, iron, and nickel.

There are 2 types of MPI:

  • Dry Magnetic Particle Testing: dry particles are dusted onto the surface of the test component as the item is magnetised. This method is well-suited for test materials with rough surfaces.
  • Wet Magnetic Particle Testing: magnetic particles are suspended in water or oil. This method is more sensitive to flux leakage sites caused by defects than the dry technique as the particles are able to be more mobile in this suspended state.


Why is Magnetic Particle Inspection used

The purpose of MPI is to identify defects in good time in order to prevent premature or unexpected machine failure which can result in accidents, loss of productivity and costly downtime.

  • Can be performed quickly and portably.
  • Is relatively inexpensive and doesn’t require stringent pre-cleaning.
  • Can be performed on large or small objects.
  • Indication of defects can be seen immediately.
  • Can be used to inspect components with irregular shapes (crankshafts, connecting rods etc), and on surfaces that have other materials on them.
  • Identifies surface and near surface defects (areas which concentrate stresses)
  • Sensitive enough to detect shallow and fine cracks.