Stress intensification factor, sustained stress index and flexibility factor analysis of large D/T elbows

Abstract

Paper presents new equations for calculation of stress intensification factors, sustained stress indices and flexibility factors for large diameter-to-thickness ratio elbows (i.e., D/T>100). The proposed equations overcome the need for pipe stress engineers to use numerical analyses in order to evaluate the piping which falls outside of the scope of typically used piping design codes. Regression analysis of the newly proposed equations is based on an extensive numerical database developed specifically for purposes of this paper, alongside with the data (both numerical and empirical) found in the open literature. Proposed equations prove to be a better fit to the database than the existing equations and have been shown to be applicable not only for large pipes, but also for normal piping (having D/T lt = 100) typically found in industrial plants. In case of the adoption of the proposed procedure, it is implied that the proposed equations should be applied to all the bends within a piping system subject to the analysis and not only to the selected bends.