Prior to an inspection, the test instrument is set up and calibrated using a probe having the appropriate coil configuration for the type and alloy of the tubes being inspected.
Apply an alternating current (Typically 10Hz-10MHz) through a coil.
Generating an eddy current
An alternating magnetic field will have induced circulating electric currents (eddy currents) in the component that is under inspection. The eddy currents alter the magnetic field of the coil and thus its impedance.
Detecting an eddy current
Any presence of cracks will cause changes to the eddy currents and to the magnetic field.
These can be detected via the coil impedance or directly using a further coil or other magnetic field sensor.
Adaptable surface eddy current array screening tool for detection of SCC, cracks and other defects – Courtesy of Eddyfi Technologies
