Measurement and response law of crack defects in X-type eddy current probe

Eddy current testing and CIVA simulation were carried out for various surface defects, especially PWSCC in reactor vessel head (RPVH) to determine the detection capability and the sizing rules of X-type point probe. X-type point probe can distinguish the direction of defects, and the axial and circumferential crack have the maximum defect responses. The minimum detection capability of depth and length is 0.2 mm and 1 mm receptively, and the signal amplitude increases slowly when depth is ≥2.5-3 mm. The method of -6 dB length measurement has also been verified and can be applied. X-type coil surface probes were applied in the AP1000 PRVH pre-service inspection for the first time to evaluate the integrated performance, including signal to noise ratio and the lift-off. The results satisfy the code, and the length measurement and position is precise.