Electrical properties analysis of ECT bobbin probe for S/G tubing inspection

Eddy current test (ECT) is one of non-destructive tests, which detects imperfection by measuring impedance change in the test coil caused by eddy current induced in an electrically conductive material. The ECT for steam generator tube in nuclear power plant is the most important non-destructive test during the plant outage. Bobbin coil probe is the most commonly used for the steam generator tubing inspection. The type of bobbin coil probe to be used for the inspection depends on the characteristics of steam generator tube such as the material and geometry of the tube. The electric properties, especially the impedance, of the bobbin coil probe is related to the geometry of the coil. In this study, a system for acquiring the impedance data was made up and a computer program was designed for effective data acquisition. Employing the system and program, the resonance frequencies were obtained and the impedance data were acquired for the bobbin probes for the steam generator tubing inspection. Experimental results are compared with the theoretical results and normalized impedance diagrams for the probes are offered in this paper. These experimental results gives not only a better understanding of electric properties of the bobbin probes for steam generator tubing inspection but also the information about the design and fabrication of the bobbin probes.