A Review of IGSCC Susceptibility of Precipitation Hardened Alloy X-750

The susceptibility of LWR components to SCC continues to be governed by the operating environment as well as the microstructure of the structural materials used for key components.  In operating BWRs, significant efforts have been undertaken to proactively address SCC through mitigation measures that reduce the corrosion potential within the vessel.  However, the effects of high strength, which necessitated by material requirements or imparted by irradiation hardening or surface cold work, heighten the potential for SCC initiation.  The objective of this paper is to review efforts to understand the effects of metal processing history, resultant microstructure, applied stress and water chemistry on the susceptibility of one high strength Ni-base alloy, Alloy X750.  The paper will review the current incidences of cracking as well as efforts to proactively manage cracking.  A review of the microstructural features that affect susceptibility will be used to develop guidelines to avoid cracking.  Using Alloy X-750 as the baseline, behavior of alternate alloys will then be discussed in the context of developing robust components for future use.  The types of testing needed to support these alloys will also be presented in the context of current engineering evaluation needs.