Evaluation of plastic limit load of piping branch junctions subjected to out-of-plane moment loadings

Abstract

Under out-of-plane moment loadings, the piping branch junctions (also called tees in engineering) exhibit three kinds of failure mode, namely collapse failure of the branch pipe, global collapse of the intersection due to plastic hinges forming along the intersection line and local instability of the main pipe at the flank. In this work, the common piping branch junctions utilized in petrochemical and power industries with a failure mode of global collapse were investigated, and a new approximate formula for an out-of-plane plastic limit moment was presented. The formula was built on the following process: firstly, an equation between the out-of-plane limit moment and internal force of the branch pipe along the intersection is set up on the basis of the force equilibrium condition. Regarding this internal force as an external load for the main pipe shell, the internal force and moment along the intersection of the main pipe, under the plastic limit state, are then obtained. Finally, referring to the von Mises yield criterion, the approximate plastic limit load of the piping branch junctions subjected to the out-of-plane moment is derived. The accuracy of the new formula is validated by comparison with finite element analysis and experimental results.