ULTRASONIC FLAW DETECTION OF WELD ZONE OF PIPE

摘要

PURPOSE:To determine the presence or absence of any defect in a weld zone accurately by calculating the arithmetic average value of the decibel value of a received ultrasonic wave, and determining the deviation between said arithmetic average value and the received decibel value of the ultrasonic wave across the weld zone. CONSTITUTION:A transmission probe 3a and a reception probe 3b are set equally dividedly on both sides. While an ultrasonic wave is transmitted through a weld zone 2 across the same in the axial center P direction of a pipe, both probes 3a, 3b are moved at an equal speed integrally in the circumferential direction of the pipe. the correlation between the change in the flaw detection position in the circumferential direction of the pipe and the change in the max. satd. decibel value W(dB) of the ultrasonic wave received by the probe 3 is recorded automatically and continuously like solid lines on a graph. The similar recording is accomplished with an upper pipe 1a and a lower pipe 1b as well. The presence of a defect is decided in the place where the value W(dB) is smaller than an evaluation line-X and the tendency toward the progression of the defect is detected quantitatively in accordance with the width l of the defect present in the circumferential direction of the pipe and the distribution of the defect, whereby the life of the weld zone 2 is predicted.