Magnetic Flux Leakage 

MFL – Magnetic Flux Leakage is an NDT technique which detects loss in volume of a magnetic material caused by corrosion or erosion. MFL locates defects by using a sensor to detect the magnetic field which is squeezed out of the metal wall under test by any decrease in the wall thickness. The sensor is usually one of two types:
  • a passive coil sensor – as the coil moves through the magnetic flux a current is induced and can be detected;
  • a hall effect sensor – an electronic device which measures absolute magnetic field strength.
The MFL technique can detect material loss defects on both the inner or outer surface of the component under test. The wall thickness that can be inspected by Magnetic Flux Leakage is limited by the requirement to achieve magnetic saturation and is generally 15 mm or less.

This technique has found widespread use in the inspection of storage tank floors from the inside of the tank and in the in-service inspection of pipelines.

For more information on Magnetic Flux Leakage see:
'Magnetic Flux Leakage (MFL) Technology For Natural Gas Pipeline Inspection' at

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