Effects of Magnetic Phase on the ECT Signal in the SG Tubes

The magnetic phase created in the Inconel alloy which is called permeability variation cluster (PVC) results in the distortion of an eddy current test (ECT) signal during the inspection of steam generator (SG) of a nuclear power plant (NPP). The effects of magnetic phase on ECT signals were analyzed using the inspection data of NPP. The hysteresis loops were measured for the PVC which is extracted from retired SG tubes of Kori-1 NPP. The tensile tests were performed to identify the mechanism of PVC creation. The coercivity of PVC is larger than 200 Oe, and hysteresis loop appeared in the tensile tested specimen at 600°C.