Ultrasonic inspection of studs (bolts) using dynamic predictivedeconvolution and wave shaping

摘要

Bolt degradation has become a major issue in the nuclear industrynsince the 1980's. If small cracks in stud bolts are not detected earlynenough, they grow rapidly and cause catastrophic disasters. Theirndetection, despite its importance, is known to be a very difficultnproblem due to the complicated structures of the stud bolts. This papernpresents a method of detecting and sizing a small crack in the rootnbetween two adjacent crests in threads. The key idea is from the factnthat the mode-converted Rayleigh wave travels slowly down the face ofnthe crack and turns from the intersection of the crack and the root ofnthread to the transducer. Thus, when a crack exists, a small delayednpulse due to the Rayleigh wave is detected between large regularlynspaced pulses from the thread. The delay time is the same as thenpropagation delay time of the slow Rayleigh wave and is proportional tonthe site of the crack. To efficiently detect the slow Rayleigh wave,nthree methods based on digital signal processing are proposed: wavenshaping, dynamic predictive deconvolution, and dynamic predictivendeconvolution combined with wave shaping