Stress Intensification Factor Calculation of Pipe Attachments Through FEA

Abstract

In Section III of the ASME Boiler and Pressure Vessel Code, the design equation for primary stresses in piping, contains stress equations for straight pipes that are modified by stress indices so that the equations can be applied to other piping components. B2 and C2 stress indices are needed for evaluation of various piping components. These indices are used in calculation of stress terms corresponding to moment loading.

When an external load is applied to one of its ends, the pipe bend’s cross-section tends to deform significantly both in and out of its own plane. This shell-type behavior characteristic of pipe bends accounts for their greater flexibility. This added flexibility is mainly due to their curved geometry, and also accompanied by stresses and strains that are much higher than those present in a straight pipe of the same size and material, under the same loading conditions. For this reason, pipe bends are considered the critical components of a piping system. Hence, for the purpose of designing and/or qualifying a pipeline structurally, it is useful to have a reliable estimate of their load-carrying capacity. Therefore in this dissertation main concentration has been given to elbows. Along with elbow other attachments like elbow-trunnion, pipe-trunnion and header-branch are also considered for the study of their SIFs.

The primary goal of this project is to study the stress intensification factor of pipe attachments through finite element analysis, under in-plane and out-of -plane moment loading. Two approaches have been utilized to study the stress intensification factors called non-linear inelastic approach and linear elastic approach. Results from both approaches have been compared with code-defined values. Experimental and analytical studies were conducted to demonstrate that FEA can simulate the nonlinear behavior of elbows and straight pipes under monotonic loadings within engineering accuracy. Here experimental results have been adopted for correlation with finite element analysis.