DEFECT DECIDING METHOD FOR ULTRASONIC FLAW DETECTION OF SEAL WELD ZONE OF RESISTANCE WELDED TUBE

摘要

PURPOSE:To decide a defect in the seam weld zone of the resistance welded tube by using both a 1st set reference as an acceptance/rejection criterior determined by specifications and a 2nd set reference wherein a defective sample is cut from a pipe which emits a reflection echo in a right-left direction and a weld defect is set in combination. CONSTITUTION:Ultrasonic waves 2L and 2R are made incident opposite each other in a left and a right direction close to the outer peripheral surface of the seam weld zone of the resistance welded tube 1 and the 1st set reference R1 wherein there is a weld defect when even one of reflection echoes exceeds a specific level is provided. Further, the 2nd set reference R2 is set wherein a weld defect is decided when the reflection echoes in the left and right directions are generated at the same lengthwise position in the seam weld zone. The weld defect is present vertically from the surface of the resistance welded tube 1, so the reflection echoes of the ultrasonic waves 2L and 2R are nearly equal in level. A flaw 5 other than the weld defect is prevent slantingly, so the reflection echoes of the ultrasonic waves 2L and 2R are different in level. For the purpose, both the reference R1 and R2 are used in combination to make a high-accuracy decision.