| 摘要 |
PROBLEM TO BE SOLVED: To enhance the reflection intensity of ultrasonic waves from a defect and make reducible noises caused by echoes from a reinforcement of weld of a weld part and a weld metal or the like by setting the flaw detection refraction angle of ultrasonic waves sent into a steel pipe from an oblique probe to an angle with which the ultrasonic waves enter the plane defect perpendicularly. SOLUTION: A probe-selecting operating apparatus 11 operates an appropriate flaw detection refraction angle θ for detecting a plane defect 4 spreading in the thickness direction and axial direction within a weld part 3 in accordance with a thickness (t) and an outer diameter D of a steel pipe 1 to be inspected. Moreover, the apparatus selects an oblique probe 5 which can detect a defect with the flaw detection refraction angle θ and operates an incidence angle (i) of an ultrasonic wave 6 to an outer circumferential face 2 of the steel pipe 1. The probe-selecting operating apparatus 11 calculates the flaw detect refraction angle θ according to formula I from the thickness (t) and the outer diameter D. At the same time, the apparatus calculates the incidence angle (i) in a propagation direction of the ultrasonic wave 6 within the oblique probe 5, that is, incidence angle to the outer circumferential face 2 of the steel pipe 1 according to formula II in which Vm, V are respectively a sound velocity of the longitudinal wave of the ultrasonic wave in an edge and a sound velocity of a transversal wave of the steel pipe 1. |
