Additional Improvements to Appendix G of ASME Section XI Code for Nozzles

Abstract

This paper is the second in a continuing series of papers to highlight additional bases and recommended improvements to Appendix G. In 2008, the authors prepared a paper that reviewed some of the original basis documents for Appendix G for calculating pressure-temperature (P-T) limits and identified recommended areas for improvement. The 2008 paper discussed the fact that the original Appendix G in Section XI of the ASME Code was primarily based on Welding Research Council (WRC) Bulletin 175, and identified the changes that have been made to Appendix G over the past 20 years. However, the nozzle corner solutions have remained the same as those given in WRC 175. Proposed revisions to Appendix G are included in this paper regarding the stress intensity factor (K) calculation procedures for pressure and thermal gradient loading at a nozzle corner based on the various solutions described in the authors’ previous paper and on other more recent investigations. The current paper is focused on incorporating the results of additional studies that have been completed associated with nozzle corner solutions. This additional work has become more important because plants must address the effects of nozzles in the reactor pressure vessel (RPV) as a part of pressure-temperature (P-T) curve development, especially if the nozzles are located sufficiently close to the active core region such that they accumulate significant fluence. In addition, the treatment of operating stresses exceeding the material yield stress is discussed and the basis for the limit of material yield strength to 90 ksi in G-2110(b) is provided. Finally, this paper identifies other areas for future improvements in Appendix G, including those areas remaining to be addressed from prior work.