From the early 1980’s to the present time, there has been a significant amount of research and development on the structural integrity of nuclear power plant piping. From those efforts, there are a number of lessons that could be applied to design and fabrication of new nuclear power plant piping systems. In this paper, the various aspects evaluated in NRC-funded efforts for understanding degraded piping were reviewed and implications on how to avoid detrimental aspects were discussed, as well as some more recent efforts. Some of these aspects include; (1) materials aspects (variability of wrought stainless steel base metal toughness with composition, dynamic strain aging effects on toughness of ferritic steels, fracture toughness in HAZ/fusion lines, material anisotropy effects on toughness, effects of static versus dynamic loading on material toughness, cyclic loading effects during seismic loading on toughness, thermal aging effects on strength and toughness), (2) designing weld sequencing to avoid SCC cracking; (3) crack morphology effects on leak-rate evaluations, (4) system effects that can significantly affect the structural integrity analysis of the piping system (secondary stresses, restraint of pressure induced bending, system displacement and rotation constraints, and margins associated from full dynamic analyses).

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