Abstract
Code Case N-755 and ASME Section III Appendix XXVI were developed by ASME for providing deterministic rules for new construction of Class 3 buried piping using High Density Polyethylene (HDPE) piping. These rules contain many special treatment requirements consistent with deterministic rule making, that have essentially put HDPE out of economic contention with other choices for replacement of degraded buried Class 3 piping such as using thicker-walled carbon steel piping, low alloy piping material, or even AL6XN. Re-evaluation of buried portions of Class 3 safety-related service water and cooling water piping using the risk-informed provisions of 10 CFR 50.69 or Code Case N-752 should result in recategorization of most buried Class 3 service water piping as Low Safety Significant, enabling relaxation of many of those special treatment requirements.
This paper describes an approach that will apply ASME Section III Appendix XXVI for replacement of Class 3 buried piping categorized as Low Safety Significant while exempting the design and construction from several special treatment requirements of Section III Appendix XXVI. This approach provides alternative treatment provisions for material procurement, design, fabrication, installation, and testing of technically superior HDPE piping as a cost-competitive permanent replacement for degraded buried safety related Class 3 carbon steel piping.
