| 摘要 |
PURPOSE:To prevent infiltration of water in a surface of a steel pipe, by a method wherein an ultrasonic wave is made incident through the outer surface of the steel pipe to implement a lamination flaw detection to enable the identification in the equipment with a ultrasonic flaw detector mechanism part used at parts other than the beveled part of the steel pipe. CONSTITUTION:An ultrasonic wave is made incident into a outer surface 3 of a steel pipe 1 from outside it 1 and a position of probe 5 is so set to meet angle theta of diffraction by a transverse wave. An ultrasonic beam 7 from the probe 5 is incident into the outer surface 3 at an angle gamma of incidence and reflection to generate a surface echo (S). Thereafter, the beam 7 propagates through the steel pipe 1 at the diffraction angle theta of a transverse wave and is incident into the surface of a bevel-worked part 2 of the steel pipe at an angle betaof incidence diffraction to generate a surface echo SB. The reflected beam 7 continues to propagate through in such a manner to hit an inner surface 4 of the steel pipe vertically. The beam 7 propagating through the steel pipe 1 is reflected at a defect 8 and in the case of a lamination defect, the reflection surface of which is at the right angle to the direction of the beam 7 and parallel with the inner and outer surface of the pipe, it is received by the probe 5 in the same path as the incident direction of the beam 7. Thus, a detection echo (F) is obtained. If no defect exist, a bottom surface echo (B) reflected on the inner surface is obtained.
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