Degradation detection of material used in nuclear power plant components applying probe-type eddy current sensor. Pt. 2. Detection of fatigue and irradiation embrittlement in low alloy steel for reactor pressure vessel

Fatigue damage and neutron irradiation embrittlement in low alloy steel used for a reactor pressure vessel were detected using an eddy current method where the frequency was changed in steps of 1 kHz ; output signal from the coil were processed by a phase detection technique and displayed on a complex plane as a trajectory. By comparing the trajectory of a nondegraded material with that of a degraded material, degradation was evaluated quantitatively. Drawing such trajectory enabled us to capture the eddy current behavior totally. Increase in averaged radius of trajectory can be regarded as the increase in magnetic permeability of the material and decrease in averaged phase angle as the increase in electric conductivity. It was shown that fatigue brought about the increase in averaged phase angle, therefore the decrease in electric conductivity ; and neutron irradiation embrittlement, the decrease in averaged phase angle, therefore the increase in electric conductivity. (author)