| 摘要 |
PURPOSE:To certainly detect the flaw of a molten metal part, in the flaw detection of the longitudinal welding part of an austenite stainless steel pipe, by allowing the ultrasonic beam from a transverse wave oblique probe to be steel pipe and refracting said beam at a specific angle of refraction with respect to the steel pipe to propagate the same through said steel pipe. CONSTITUTION:The molten metal internal flaw part 2 present in the longitudinal velding part of an austenite stainless steel pipe 1 is detected. At this time, ultrasonic beam is allowed to be incident to the steel pipe 1 from a transverse wave oblique probe 3 so as to set the angle theta1 of refraction with respect to the steel pipe 1 to 33 deg. or less at the incident position. The ultrasonic beam is reflected from the outer surface P of the steel pipe 1 and subjected to mode conversion from a transverse wave to a vertical wave. The angle theta3 of reflection of the ultrasonic beam becomes two times the angle theta1 of refraction on the outer surface P on the basis of a normal line OP (O is the center of the steel pipe 1) and the reflected beam thereof is incident on the flaw part 2 vertically (theta2=90 deg.). The echo reflected from the flaw part 2 again passes through the same path to be returned to the probe 3 and converted to an electric signal to detect a flaw. Since the ultrasonic beam is allowed to be incident on the steel pipe at the angle of refraction of 33 deg. or less with respect to said pipe, the flaw can detected with good resolving power. |
