8. Subsection NB, NC, ND-3600 Piping
Mark Gray holds a Master of Mechanical Engineering degree and a Nuclear Engineering certificate from the University of Pittsburgh. He is a Fellow Engineer with Westinghouse Electric Company near Pittsburgh, Pennsylvania, employed there since 1981. His work areas have included piping and component stress and fatigue analyses, industry issues such as thermal stratification and environmentally assisted fatigue, and fatigue aging management and monitoring. He has authored over twenty conference papers or journal articles, and numerous industry reports.
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This chapter provides a commentary on the criteria and basis for requirements of Subsections NB, NC, and ND for Piping. It presents information on the corresponding design processes and design specifications, with pertinent references, tables, and figures. The chapter addresses service limits and loading conditions classified as Levels A, B, C, and D. The Code rules assure that violation of the pressure boundary will not occur if the design specification satisfactorily addresses all issues necessary for Code compliance. This assurance is provided in the following ways: protection against catastrophic failure and protection against initiation and propagation of a crack or propagation of a Section III acceptable flaw through the pressure boundary. The chapter addresses how Section III provides this protection, any variations that exist or that have existed between the piping rules and the design-by-analysis rules, and what items the analyst should be concerned with in satisfying Code requirements. It helps alleviate the confusion regarding the proper application of ANSI B31.7 rules. As the requirements of NB-3600 are discussed, the important areas are compared to those of NB-3200. The chapter also shows that for primary stress protection, NB-3200 and NB-3600 are quite different, but in the secondary and peak stress areas, including fatigue, the basis for the rules is essentially the same although the analytical approach is quite different. It then covers rules for both Class 2 (NC-3600) and Class 3 (ND-3600) piping design. The chapter also explains the importance of a design specification. Finally, it discusses the need for a process of analysis with release of information that needs to be established to provide an orderly flow of information, to assure timely pipe fabrication and support delivery, and to issue stress reports at reasonable times.
Donald F. Landers was the original author who updated the chapter for the second and third editions. The fourth edition was revised by Jack R. Cole. The fifth edition was updated by Jack R. Cole and Mark A. Gray are. The current online edition was updated by Mark A. Gray and reviewed by George Z. Tokarski.