B2 stress index for structurally distorted pipe bends under in-plane opening bending moment

Abstract

The present study determines the effect of shape imperfections on the B2 index of pipe bends subjected to in-plane opening moment using 3D nonlinear finite element (FE) methodology. The analysis considers the large strain formulation option and the material behavior is elastic-perfectly plastic. The reaction moment versus angular rotation curves are plotted for all the simulated pipe bends and the plastic collapsing moments are determined using Twice-elastic slope technique as recommended in ASME B&PV, section III (clause NB-3213.25). The B2 stress index was computed for each model from their respective collapse moment. The variable wall thickening in the pipe bend's cross section yields negligible effect and the presence of ovality has a momentous effect on B2 stress indices. A mathematical equation is suggested to compute B2 stress index for pipe bends with ovality subjected to in-plane opening bending moment.