ULTRASONIC FLAW DETECTING METHOD, MANUFACTURING METHOD FOR WELDED STEEL PIPE, AND ULTRASONIC FLAW DETECTING APPARATUS

摘要

By an ultrasonic flaw detection method according to the invention, an angle probe is provided on the outer surface of a welded steel pipe so that the propagation direction of a transverse ultrasonic beam in the welded steel pipe is approximately perpendicular to the lengthwise direction of a weld bead and a transverse ultrasonic beam having a refraction angle of at least 40° and less than 55° is propagated to one of both toes of the weld bead at the inner surface of the welded steel pipe that has a shorter distance to the angle probe. After providing the probe, the welded steel pipe is probed using the angle probe and it is determined, based on the result of flaw detection, whether or not there is an inner surface toe crack that extends from the toe to the inside of the base and is inclined to the opposite side to the weld bead with respect to the radial direction of the welded steel pipe. Therefore, the capability of detecting inner surface toe cracks generated at the toes of a weld bead at the inner surface of a welded steel pipe can be improved.