Study on ultrasonic testing conditions for an axial flaw in a taper of pipe elbow on weld piping (2)

Ultrasonic testing has been thought to be difficult to apply to cast stainless steel which is used for reactor coolant pipes or other components in pressurized water reactors (PWRs), because of the large attenuation of ultrasonic waves caused by the material columnar structure. A twin crystal transducer probe and an automatic ultrasonic testing system using the probe were developed in INSS. This probe, however, cannot detect axial flaws on inner surfaces of the tapers of elbow pipes, as it cannot be scanned on outer surfaces of the tapers. In this paper the conditions to discern echoes from the axial flaws on inner surfaces of the tapers of pipe elbows were studied in the case that ultrasonic waves were incident at an angle from the possible-to-scan zone by ultrasonic testing simulation. As a result, it was found that the probe skew method in which the probe faced the flaw was suitable and the skewed angle between 40 and 60 degrees, which is the angle at which ultrasonic waves are obliquely incident in the flaw direction, had high signal intensity from the flaw. (author)