Phase Distinction in Eddy Current Testing for Steel Tubes

In the eddy current testing for steel tubes, the saturated magnetization was needed in order to reduce the effect of the magnetic permeability uncertainly. There was a problem that the phases of defect signals could not be distinguished sometimes. Theoretical analysis and experimental results showed that there were two effects, eddy current effect and magnetic flux leakage effect in this situation. When the magnetization intensity of the tubes was oversaturated, the magnetic flux leakage effect was dominant. As the signals from magnetic flux leakage effect were not related to the phase, there was no way to distinguish defects through their phase difference. On the other hand, when the magnetization was proper, the phase difference of the signal for different defects was very clear. It was the same that the appearance of testing signals in the impedance chart as the one for non-ferromagnetic materials.