Final results of the NESC-III non-destructive testing blind round robin trials on dissimilar metal welds

Recent problems identified in some nuclear power plants with the characterisation of defects of complex morphology, such as primary water stress corrosion cracking, have again cast doubt on the effectiveness of ultrasonic inspection. There is therefore a need for re-assessment of the capability of in-service inspection methods, especially for inspection of dissimilar metal welds, which continues to be difficult. The level of performance of ultrasonic inspection in defect detection and sizing, which was demonstrated in earlier PISC exercises, is not well aligned with the needs of structural integrity analysis. Development in ultrasonic inspection, for example the trend towards increasing use of phased array probes and tip diffraction methods for sizing, are claimed to deliver significantly improved inspection performance. In order to understand the current capabilities of modern inspection methods, a blind round robin trial was launched in the NESC-III project looking at two different dissimilar metal welds. This paper provides a synthesis of the entire inspection trial programme and presents the key results for both detection and sizing of the defects. Finally it gives the main conclusions and recommendations appearing from the study, which have been agreed unanimously by all participants in the study.