Evaluation of Near/Far Field and Directivity of Ultrasonic Transducer for Turbine Rotor Disc

Near/far field length and directivity of transducers were investigated for the improvement and evaluation of the detectability of flaws in a disc. The reference block is fabricated for the disc of stage 6 in Yonggwang unit 1. The near/far field and directivity of an ultrasonic transducer with the center frequency of 5MHz were calculated for the inspection of the disc. These values showed good agreements with the experimental results. In the system composed of a wedge and a disc, those are evaluated theoretically and experimentally for the specimen with the artificial flaws of the size 2mm and 4mm and an ultrasonic transducer with the center frequency 5MHz and diameter 0.5 inch. The detectability of keyway-flaw and detectable region for inspection were evaluated by using both tangential 45 .deg. and 90 .deg. transducers located at the distance of 53mm and 75mm from the disc hub, respectively