Eddy Current Principle
Eddy Current Inspection is a technique used for the surface inspection of conducting materials.
By placing a coil carrying an alternating current (excitation current), eddy (surface) currents are induced in the conducting surface (pipe surface).
It leads to a change in the inductance (electrical characteristics of the coil) of the sensing coil.
By measuring these changes, a surface profile can be created for the pipe surface.
The surface profile can be used to identify corrosion, metal loss, opening, and general pitting.
In most cases, an eddy current sensor is used in conjunction with MFL sensors to discriminate external anomalies from internal.
When an eddy current sensor is used with MFL, it is referred to as ID/OD sensor or coil sensor.
The resolution of the eddy current is reduced when used as ID/OD since the MFL has higher resolution and measurement abilities. In this case, the eddy current sensor is used for discrimination of anomaly position (external/internal).
Eddy Current Technology can also be used in standalone cases to inspect internal corrosion of high wall thickness pipe where MFL has less probability of success.