Evaluation of back-side flaws of the bottom plates of an oil-storage tank by the RFECT

In the present study, the remote field eddy current testing (RFECT) was used to detect back-side local corrosion in the bottom plates of an oil storage tank constructed of a ferromagnetic material. A phenomenon similar to a remote field for a tube-type test piece was confirmed in this measurement system with/without the U-type component. The appropriate distance between the excitation coil and the pick-up coil and the excitation frequency were experimentally examined to detect the back-side flaws of ferromagnetic plates. In addition, using the proposed method, back-side flaws of ferromagnetic plates were evaluated with the phase change of the measured signals of the pick-up coil.