Modeling the interaction of SLIC transuducers with cracks in reactor pressure vessel steel

The integrity of reactor pressure vessels (RPV) is primarily affected by the presence of near-surface fatigue cracks. Novel transmit-receive transducers which simultaneously use shear and longitudinal waves for material inspection and flaw characterization (SLIC) have recently been qualified to detect and fully characterize as to type, size, location, and orientation flaws in cladded RPV test specimens. These multibeam/multimode transducers produce readily observable, recordable, and predictable (hence interpretable) pulse patterns which bear unique temporal and spatial relationships to several important characteristics of the insonified flaw. The two-step approach to ultrasonic evaluation of RPVs for near-surface fatigue cracks is presented. Cracks are detected with the SLIC-40 multibeam transducer and sized accurately with the SLIC-50 multimode transducer. Computer models of the multiple (hence highly informative) interactions of these transducers with semielliptical fatigue cracks were developed and verified in the laboratory using notches and cracks with known characteristics