The history of the primary stress design equations for Class 1 and 2 elbows in the ASME Boiler and Pressure Vessel Code (Section III, Division 1, Subsections NB and NC) is reviewed. The review includes the early analytical solutions for elbow bending, Markl’s stress-intensification factor, the development of Code equation (9), the relationship between SIFs and the and stress indices, development of equations that are functions of internal pressure and bend angle, and a suggested definition of the index which is based on nonlinear finite element analysis.
The History of the Stress Index
Contributed by the Pressure Vessels and Piping Division for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received by the PVP Division, September 25, 2000; revised manuscript received January 29, 2002. Associate Editor: G. C. Slagis.
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Matzen, V. C., and Tan, Y. (May 1, 2002). "The History of the Stress Index ." ASME. J. Pressure Vessel Technol. May 2002; 124(2): 168–176. https://doi.org/10.1115/1.1464564
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