The History of the B2 Stress Index

Abstract

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 C2 and B2 stress indices, development of B2 equations that are functions of internal pressure and bend angle, and a suggested definition of the B2 index which is based on nonlinear finite element analysis.