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Applications of Magnetic Particle Testing (MT)

Magnetic particle inspections work by running a magnetic current through the material that is being inspected.

When the current is interrupted by a discontinuity; magnetic flux lines change direction to follow the easiest path (same as when an stream of river is diverted and goes around a blockade), indicating its presence by re-arrangement of magnetic particles that follow the magnetic flux lines; therefore allowing inspectors to identify its location in the material.

ADVANTAGES OF MT

• It is quick and relatively uncomplicated.
• It gives immediate indications of defects.
• It shows surface and near surface defects, and these are the most serious ones as they concentrate stresses.
• The method can be adapted for site or workshop use.
• It is inexpensive compared to radiography.
• Large or small objects can be examined.
• Elaborate pre-cleaning is not necessary.

LIMITATIONS OF MT

• It is restricted to ferromagnetic materials – usually iron and steel, and cannot be used on austenitic stainless steel.
• It is messy.
• Most methods need a supply of electricity.
• It is sometimes unclear whether the magnetic field is sufficiently strong to give good indications.
• The method cannot be used if a thick paint coating is present
• Spurious, or non-relevant indications, are probable, and thus interpretation is a skilled task.
• Some of the paints and particle suspension fluids can give a fume or fire problem, particularly in a confined space.