Stress corrosion cracking (SCC), though infrequent, is often detected in nuclear power reactor system piping and components. A number of approaches have been developed and successfully deployed for SCC repair and mitigation such as full structural weld overlay (FSWOL), optimized weld overlay (OWOL), and mechanical stress improvement process (MSIP). While these approaches are proven technologies and have served the industry well, a new strategy, excavate and weld repair (EWR), provides yet another option for repair or mitigation of SCC. The EWR approach excavates a portion of the outer part of the butt weld. The excavation is then filled with a weld metal with demonstrated SCC resistance. The EWR approach would require less welding compared to a weld overlay and may be the best option for large bore butt welds where restricted access may make FSWOL, OWOL, or MSIP impractical. For the situation where a flaw is detected and removal or reduction of the flaw to acceptable size is necessary for continued service, the approach would permit a local partial arc EWR where only a portion of the butt weld circumference is removed and repaired. While the partial arc EWR is not a full mitigation, it would provide the needed preparation time for a more permanent repair during a subsequent refueling or maintenance outage. ASME Code Case N-847 was developed to provide examination, design, installation, and preservice/inservice inspection requirements for the EWR repair and mitigation approach. This paper provides a background, description and the technical bases for the EWR case case.

This content is only available via PDF.
You do not currently have access to this content.