Low frequency eddy current inspection of wall-thinning of large pipes by bobbin coils

This study firstly discussed effect of three coil´s orientations on sensitivity of low frequency eddy current testing for inspecting wall-thinning of large pipes through experimental signals. One specimen made of carbon steel was prepared. Hollows with different depth were introduced on the bottom of the specimen. Results of experiments showed that sensitivity of low frequency eddy current testing would be best if axes of bobbin coils are both parallel to surface of a pipe. Further experimental data showed that usage of coils´ shield could not improve the sensitivity of inspection. Subsequent simulations were performed to reveal the mechanism.