6 Subsection NB—Class 1 Components
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Chapter 6 originally authored by John Hechmer for the first edition and updated by Greg Hollinger for the second edition has been largely revised by David Jones for the current third edition. Authors cover Subsection NB, Class 1 Components. In presenting the rules and requirements for Section III, Subsection NB, the authors discuss the theories, on which the rules and requirements are based, the appropriate application for applying the rules and requirements, and the interfaces for design, analysis, and construction. The chapter emphasizes the analytical rules and requirements, and makes reference to the Criteria of the ASME Boiler and Pressure Vessel Code for Design by Analysis in Sections III and VIII, Division 2, 1968 that is considered the basis document for Sections III and VIII. John provided the design theory and ramifications of the key considerations, with cross-references to other Code Sections discussing the subtle differences between the Section III design criteria and the Section I and Section VIII, Division 1 design criteria.
In addition, commentary is provided on the Code requirements of Class 1 for design by analysis “because of the prominent role played by stress analysis in designing vessels by the rules of Section III … and because of the necessity to integrate the design and analysis efforts.”—The authors emphasize that the design by analysis theme of NB is to provide high assurance that the failure modes of burst, plastic collapse, excessive plastic deformation, fatigue, ratcheting, brittle fracture, elastic instability (buckling), stress corrosion, and corrosion fatigue. The intent of the rules of NB is to provide assurance that high quality is reached; therefore, stress analysis is added to the “NB rules for all of the disciplines and their interaction” in an effort to reach high quality. Chapter 6 has been updated by Greg Hollinger and David Jones to the 2007 version of the Code including discussions of the differences between Section VIII Division 2 and Section III NB. Discussions have been added on the Section VIII Division 2 rules dealing with Limit Analysis, Finite Element Analysis and Environmental Fatigue, and new methods for fatigue of weldments.