| 摘要 |
PURPOSE:To improve detection accuracy of a surface defect. CONSTITUTION:For detecting a surface defect, ultrasonic waves which are output from a probe 2 are focused and are vertically applied to the surface of a steel pipe 1 to be inspected by an acoustic lens 20, reflection echos by the surface are received, and then the surface defect of the material to be inspected is detected by a gate circuit 6 based on the level of a received echo. Then, the frequency where the level of the reflection echo corresponding to the height or the depth of the surface defect to be detected is arrenuated to a specified level is obtained based on a relationship among the height or depth of the surface detect, the level of the reflection echo, and the ultrasonic waves consisting of sinusoidal waves of frequencies higher than the obtained frequency is output from the probe 2. |
