Validation of NDE Techniques for Characterizing Dealloyed Regions in Aluminum-Bronze Casting Components in Essential Cooling Water Systems

Material degradation caused by selective leaching (dealloying) of aluminum in certain aluminum-bronze alloys is an environmentally induced degradation mechanism affecting piping systems containing cast components. Such material degradation has been observed in cast piping components fabricated to ASME SB-148 CA952 and CA954 specifications in ASME Code Class 3 essential cooling water systems. In-situ characterization of dealloyed regions in these components is important for determining the structural integrity of the dealloyed cast component in support of continued plant operation. A number of cast aluminum-bronze components were removed from service in support of validating non-destructive examination techniques for characterizing dealloyed regions. Prior to their removal, non-destructive examination inspections were performed to measure the extent of dealloying. The ex-service components were then destructively examined to validate non-destructive examination detection and sizing capabilities. This paper presents the results from the validation activities of the non-destructive examination technique for detecting dealloying. Good correlation was observed between the metallurgical examination and the adaptive ultrasonic imaging non-destructive examination inspection results, particularly the through-wall dealloying depth. Evidence from the metallurgical examination shows that the growth of dealloying over time is plug-like in nature (i.e., localized growth towards through-wall penetration). This paper also discusses approaches for addressing the uncertainties in non-destructive examination detection based on the destructive examinations.