Validation of a coil impedance model for simultaneous measurement of electromagnetic properties and inner diameter of a conductive tube

The remote-field eddy-current technique (RFEC) for nondestructive inspection of conductive tubes cannot differentiate inner from outer defects. Also, the measurement results are greatly affected by electromagnetic properties (electrical conductivity and magnetic permeability) of the tube. Therefore, additional, independent measurement of the electromagnetic properties as well as inner diameter is required. Commercial eddy-current systems successfully measure these parameters using a multifrequency, multicoil configuration. In this paper, we investigate the feasibility of the electromagnetic properties and inner diameter measurement with only one coil excited at one frequency. We have developed an optimization algorithm for determination of the tube properties. based on a coil impedance model. Measurements have been performed on several tubes made of different materials. The consistency of the model with the measurement results has been confirmed for investigated frequency range (1 to 50 kHz).