7 Section III: Subsections NC and ND — Class 2 and 3 Components
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In the first Edition, the principal author, Mr. Thomas J. Am, made extensive references to Section VIII, Division 2, and these references remain in both the second and third Editions. Users of this Chapter of the Companion Guide should be aware that in the 2007 Edition of the ASME Boiler and Pressure Vessel Code, Section VIII, Division 2, Alternative Rules for Construction of Pressure Vessels, was completely rewritten and revised. This “New” Section VIII, Division 2 has little conformity with the rules of “Old” Section VIII, Division 2. The rules for “Design by Analysis” were first embodied in the 1963 Edition of Section III, Nuclear Vessels, for Class A Vessels (today's Class 1 vessels), and later used as the Alternative Rules published in the 1968 Edition of Section VIII, Division 2. These design rules utilized Design Stress lntensities based on the Maximum Shear Stress Theory of Failure (the Tresca Criterion) and the design values were based on a design factor of of the Tensile Strength and of the Yield Strength. Permitted materials were restricted, and temperature limits were established at 700_F for carbon and low alloy steels, and 800_F for austenitic and high temperature alloys. Many fabrication details permitted in Section VIII, Division 1, were not included in construction details for the Alternative Rules. Section III, Class 2 vessels designed by analysis in NC-3200 still abide by the rules of the “Old” Section VIII, Division 2, up to the 2004 Edition, including the 2005 and 2006 Addenda. The “New” Section VIII, Division 2, 2007 Edition, still refers to “Design Stress Intensities,” but they are based on the Maximum Stress Theory of Failure (von Mises Criteria), and they are based on a design factor of 1/2.4 of the Tensile Strength. Many of the construction details not previously permitted have been included. Section III has not even begun to study this disparity in design and construction, and has not considered approval of the “New” Section VIII, Division 2. Therefore, in using this Chapter, do not reference the 2007 Edition of Section VIII, Division 2. All references are to the “Old” Section VIII, Division 2, 2004 Edition with 2005 and 2006 Addenda. For a complete discussion on the rewrite, please refer to Chapter 22.