8 Subsection NB, NC, ND-3600 Piping
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Previous discussion in Chapter 5 indicates that three classes of components are provided in the requirements of Section III, Division 1 . Each class can be considered a quality level, with Class 1 being the highest and Class 3 the lowest. These levels of quality exist because of the various requirements for each class in Section III that relate to the following: materials, fabrication, installation, examination, and design. Design is listed last because there is sufficient evidence to indicate that the other considerations listed are of more importance than (or at least equal to) the design requirements. The following discussion will address service limits and loading conditions classified as Levels A, B, C, and D. The Code is not responsible for this classification; instead, it is the responsibility of the owner to satisfy the regulatory and enforcement authority requirements. Once loading conditions are designated in the Design Specifications as Level A, B, C, or D, the Code provides acceptance criteria.
The Code rules assure that violation of the pressure boundary will not occur if the Design Specification satisfactorily addresses all those issues necessary for Code compliance. This assurance is provided in the following two ways:
1) protection against catastrophic failure, and
2) protection against initiation and propagation of a crack or propagation of a Section III acceptable flaw through the pressure boundary.
The following discussion on piping will address 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.