Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code has worked since the early 1990s to develop guidelines for the nuclear power industry to evaluate the serviceability of components that are adversely subjected to fatigue stresses. Results of this work formed the basis for a non-mandatory Appendix L that became part of the 1996 Addenda to the 1995 Edition of Section XI [1]. A key part of this appendix was the introduction of a damage tolerance based examination strategy designed to assure that the component will operate reliability between subsequent inspections. Since the issuance of Appendix L, new data on the flaw detection capabilities have become available, and these data show that ultrasonic inspections can detect flaws much smaller than assumed during the original development of Appendix L. This information allows for significantly smaller sizes for initial postulated flaws. Additionally, Appendix L did not address the potential for multiple fatigue crack initiation sites for a given location on the component. In 1999 the ASME Working Group on Operating Plant Criteria (WGOPC) re-established the Task Group on Operating Plant Fatigue Assessments (TGOPFA) to address these concerns. This paper summarizes the research results, supporting computations, and technical bases for TGOPFA recommended Appendix L improvements. A detailed sample calculation is presented for a PWR charging nozzle-to-pipe weld.

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