| 摘要 |
PURPOSE:To detect at least an external surface flaw of a thick steel pipe by providing artificial defects between the ultrasonic wave incidence point and external surface reflection point of the steel pipe and at the external surface reflection point, and using this steel pipe as a reference pipe. CONSTITUTION:An angle theta of incidence used for flaw detection is set to about 40 deg. and the thick steel pipe where an ultrasonic wave beam is not incident on the in-tube surface is selected as the reference pipe. Then the artificial defects (d) and (d0) are formed at an intermediate point between the incidence point and external surface arrival point and at the external surface arrival point. Then echoes Fd and Fd0 are obtained from the defects (d) and (d0) and flaw detection gates Gd and Gd0 for detecting the defects (d) and (d0) are provided. Thus, the echoes are obtained in the two flaw detection gates, so an existent sensitivity calibration program is applied to calibrate the sensitivity of the flaw detection device. For the purpose, the sensitivity calibration of the flaw detecting device and a probe 1 is carried out by using the reference pipe 2 to enable the ultrasonic flaw detection with respect to the external surface flaw of the thick steel pipe. |
