Electromagnetic Testing Chapter 3- Electromagnetic Testing

3D Magnetic Field
Fig.1
THE PRINCIPLE
The basic principle behind MFL involves magnetizing a ferrous metal
object to saturation level with a powerful magnetic field. Where the
object has no flaws, the magnetic flux will remain undisturbed.
See Fig.1
High magnetization levels are required to differentiate corrosion from
other pipeline features such as hard spots, stress and strain variations
and to minimize the effects of remanent magnetization and velocity.
Where there is internal or external metal loss, the magnetic flux leaks
from the object.
See Fig.2
In the MFL testing device, a magnetic sensor is placed between the
poles of a magnet yoke to record the leakage field by Hall-effect sensors.
Eddy current sensors integrated in the magnetic flux sensors are used to
improve the differentiation between internal and external defects.
Fig.2
Charlie Chong/ Fion Zhang
Hall-effect sensors
Hall-effect sensors
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