Discrimination of ultrasonic indications from austenitic stainless-steel pipe welds

Abstract

The inspection of butt-welded stainless-steel pipe joints in nuclear power plants is routinely performed using ultrasonic non-destructive evaluation methods. Field experience, based on conventional ultrasonic signal-amplitude criteria, shows that a large number of indications are recorded. Most of these are not due to cracks, but are inherent in the geometry of the specimen. Discrimination between crack and geometric/weld (malignant versus benign) indications is principally based on operator experience, variations in signal amplitude, and the location of the reflector. Significant differences in performance exist due mainly to operator experience, fatigue, concentration, and conventional signal-amplitude evaluation criteria. In addition, the process of distinguishing the type of indications is very time consuming, as field experience and round-robin tests have shown. In response to this inspection problem, a pattern-recognition methodology has been developed to discriminate intergranular stress-corrosion cracking from geometric/weld reflectors in austenitic stainless-steel pipes. Results demonstrate that this algorithm can provide discrimination comparable to or better than those supplied by well trained operators. Preliminary results show that the pattern-recognition algorithm approach yields a better than 90% index of performance.