Tube inspection using the remote field eddy current method: development ofa mathematical model to predict the relationship between the phase and thedepth of defect

The remote field eddy current (RFEC) method has been comprehensively applie d to the inspection of ferromagnetic tube. In order to measure the depth of flaw, it is necessary to create an evaluation curve from a standard tube w ith the material and size equivalent to those of the tube to be inspected. However, there are two problems. One is that we fail to obtain a standard t ube with the same thickness, and the other is the bigger error of evaluatio n, which results from our applying an evaluation curve from an original thi ckness of standard tube to assess the defective depth of a used tube with g eneral corrosion, a status which may be unknown to us during inspection. Th e objective of this study is to establish an evaluation curve through a mat hematical predictive model derived from skin-depth theory and a geometric r elationship on the voltage plane polar plot, the methodology of RFEC, for t echnicians to solve the problems mentioned above more easily. This study al so covers some simple experiments to prove the feasibility and applicabilit y of a mathematical predictive model. The result from the experiment has ve rified the method proposed by this study which is reliable and serviceable.