Axial Flaw Detection in Pipes with Circumferential Wave Excited by Transducers of Equi-Refraction Angle

摘要

A new ultrasonic method for evaluating axial flaw depth in pipes is proposed with circumferential shear vertical, SV, wave. When a conventional ultrasonic flaw detection technique with pipe transducers is applied to sizing of inner axial flaws in pipes, the wave amplitude reflected at the axial flaw or that transmitted through the flaw is not proportional to the flaw depth. Moreover, the received amplitude of the flaw depends on circumferential position. The reason is that the shear wave beams in the pipe are not parallel, e.g., the refraction angle into steel pipes varies with the circumference position. To improve this, a special shear wave transducer of equi-refraction angle was designed. With this transducer, the wave energy distribution along the wall thickness is nearly uniform, therefore, the transmitted wave amplitude through the flaw is expected to be proportional to the flaw depth. To confirm this, we measured the wave amplitude transmitted through an axial slot in a pipe of thickness of 3mm and diameter of 60mm. The depths of the axial slot are 33, 50 and 67 % of the thickness. The amplitude transmitted through the slots is found to be nearly proportional to the slot depth.