ULTRASONIC FLAW DETECTING METHOD FOR THICK-WALLED STEEL PIPE

PURPOSE:To enable flaw detection with a more sufficient sensitivity margin than flaw detection by a conventional longitudinal wave-transversal wave mode converting method by propagating a longitudinal wave directly to the internal surface defect of a thick-walled steel pipe. CONSTITUTION:This method is a flaw detecting method which supplies the longitudinal wave L directly to the internal surface defect by using a range of a longitudinal wave refraction angle thetaL=14-20 deg.. In this case, the acoustic pressure reciprocation passing rate of the longitudinal wave-transversal wave mode converting method is 6.8%, but that of the direct longitudinal wave method is 11.8% and 5.0% higher. Assuming that the sound pressure at a point C is 1, the sound pressure at a point C'' is about 2.8 from an ultrasonic wave beam path. Namely, flaw detection is performed by this method with a more sufficient sensitivity margin than flaw detection by the conventional longitudinal wave- transversal wave mode converting method.