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This paper presents a new hybrid spiral-bobbin probe (S-bobbin probe) of transmitting-receiving (TR) mode for efficient eddy current testing (ECT) of steam generator tubes in nuclear power plants. The new probe of novel configuration can solve the major drawback of the conventional bobbin type ECT probe, i.e., insensitive to circumferential cracks. The excitation coil of the new probe consists of 2 coil segments of spiral geometry and 2 coil segments of half circle geometry which are sequentially connected to form a full coil loop. To acquire defect signal of low lift-off noise, the TR probe mode is adopted and the shape of the pick-up coil is selected the same as that of the excitation coil. As the S-bobbin probe can induce eddy currents in two different directions, it can detect cracks in SG tubes of arbitrary orientations. In order to demonstrate the validity and efficiency of the new S-bobbin probe, simulations and experiments were carried out with a prototype S-bobbin probe and tube specimens with circumferential or axial artificial cracks. The simulation and experimental results agree well, and both of them reveal that a crack in any direction can be properly detected and evaluated by using the new probe. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of studies on the local distributed electrical conductivity in stress corrosion crack (SCC) from signals of eddy current testing (ECT) and direct current potential drop (DCPD) aiming to improve SCC sizing accuracy when using electromagnetic non-destructive testing (NDT) methods. Experimental setups of ECT and DCPD were established, respectively, to collect measurement signals due to artificial SCCs in a plate of austenitic stainless steel. The local conductivity in the SCC region was reconstructed from the feature parameters extracted from the measured ECT and DCPD signals through inverse analyses. The inversion strategies for ECT and DCPD, each including an efficient forward simulation and an optimization scheme, were introduced from the viewpoint of conductivity reconstruction. Inversion results obtained from the measured ECT and DCPD signals showed the consistent trend which proved the validity of the predicted electrical conductivity indirectly. It is clarified that the electrical conductivity in a SCC is relatively high at the crack tip area and may become as high as 17% of that of the base material. These results provide a good reference to enhance the sizing accuracy of SCC with an electromagnetic NDT method such as ECT by updating the conductive crack model based on the results of this work. This article is part of the theme issue 'Advanced electromagnetic non-destructive evaluation and smart monitoring'.