A new serpentine array eddy current probe for steam generator tubes inspection

Eddy current probes are widely used in the integrity evaluation and wall crack detection of steam generator tubes in nuclear power plants. In this paper, a new eddy current probe with serpentine array structure based on superposition principle is proposed. As the array coils of the probe are two-dimensional curved structure, the array coils can be etched on a flexible printed circuit board for better probe performance and simplification of probe packaging. The simulation results show that eddy current induced by the reverse-phase excitation probe is mainly concentrated in the central region of the adjacent coils. Consequently, through the serpentine array of coils, the superposition of eddy current components in both axial direction and circumferential direction is similar. The simulation results show that amplitude of the detection signal is approximately equal in different angles between scanning direction of the probe and defect from 0 degrees to 90 degrees, thereby achieving similar detection sensitivity of the probe in different orientations defects. Nine notches of different orientations and sizes were machined on the outer surface of the steam generator tube specimen for inspection and testing the performance of the developed probe. The probe can effectively detect the outer wall defects with a size of 2mm x 0.3mm x 0.6mm, and the experimental results demonstrated the proposed probe can reduces the influence of defects orientation on amplitude of the detection signal, so better avoid the missed defects in tubes inspection.