| 摘要 |
PURPOSE:To efficiently execute the flaw detection of electric resistance welded tubes having the same outside diameter and different wall thickness by allowing and ultrasonic wave to be made incident from the outside wall surface of the tube and propagating it in the tangential direction. CONSTITUTION:Ultrasonic wave generators U1, U2, U3 and U4 of a flaw detector are housed in an enveloped body filled with water, and an ultrasonic wave is made incident from the outer wall surface of an electric resistance welded tube 28. Subsequently, the incident angle is set so that the propagation direction at the time of refraction becomes the tangential direction of the tube 28, and the arrangement interval is set so that the tube 28 is irradiated by an ultrasonic wave at an equal interval along a weld zone W of the tube 28. In this state, a receiving means receives a reflected echo of the ultrasonic wave, a comparing means compares the reflected echo by a prescribed threshold, a recording means records the result of comparison, and a sensitivity changing means changes sensitivity of the receiving means in accordance with wall thickness of the tube. According to such a constitution, even if a droplet of soluble oil adheres to the inside surface of the tube, it does not occur that the adhering part is misconceived as a defective part, and also, even if wall thickness of the tube is different, if the outside diameter is the same, the flaw detection is executed without necessitating to change setting a position of the ultrasonic wave generator and the work efficiency of flaw detective can be improved. |
