TECHNICAL BASIS FOR ASME SECTION XI CODE CASE FOR STRESS CORROSION CRACK GROWTH RATE EVALUATIONS FOR ALLOY 690 AND ASSOCIATED WELDS

摘要

Alloy 690 and its associated weld metals (Alloys 52, 152, and variants) have been used in service as replacement materials for Alloy 600 and its associated weld metals (Alloys 82, 182, and 132) since the materials were accepted in the ASME Boiler and Pressure Vessel Code in 1989. To date, there have been no reported incidents of primary water stress corrosion cracking (PWSCC) in these replacement materials in operating plants. While this is a strong indicator that the Alloy 690 materials are resistant to PWSCC, in closely controlled laboratory experiments, PWSCC in these materials has been induced. Therefore, a need exists to characterize the PWSCC crack growth rates in Alloy 690 materials to evaluate possible cases where a) a flaw initiates in these materials in service, b) crack growth extends into these materials from existing flaws occurring in adjacent susceptible material, or c) a manufacturing defect is conservatively interpreted as PWSCC. This paper provides the technical basis for incorporating such a crack growth rate evaluation method into a Code Case in the ASME Boiler and Pressure Vessel Code. This method was developed based on PWSCC data obtained from laboratories around the world, which were compiled and screened for data quality and plant applicability by an expert panel. This paper provides a summary of the effort to develop the factor of improvement approach, which bases the predicted PWSCC growth rates of Alloy 690 and its welds on that of Alloy 600 and its welds, respectively, under similar conditions.