Plastic Limit Analysis of an Elbow with Various Wall-Thinning Geometries

Abstract

A piping system including straight pipes, elbows and tee branches in a nuclear power plant is mostly subjected to severe loading conditions with high temperature and pressure. In particular, the wall-thinning of an elbow due to flow accelerated corrosion is one of safety issues in the nuclear industry. In this respect, it is necessary to investigate the limit loads of an elbow with a wall-thinned part for evaluating integrity. In this paper, three dimensional plastic limit analyses are performed to obtain limit loads of an elbow with different bend angles as well as defect geometries under internal pressure and in-plane/out-of-plane bending moment. The limit loads are also compared with the results from limit load solutions of an uninjured elbow based on the von Mises yield criteria. Finally, the effects of significant factors, bend angle and defect shape, are quantified to estimate the exact load carrying capacity of an elbow during operation.

Effect of wall thinning on deformation and failure of copper‐nickel alloy elbows subjected to low cycle fatigue

“…12,13 There were many analytical, numerical, and experimental studies in this area with the ultimate aim of developing a method for the evaluation of low fatigue strength of various piping elements with various wall thinning defects with and without internal pressure. 2,10,11,[14][15][16][17][18][19][20][21][22][23][24][25] For steel elbows, the recent studies have demonstrated that when the elbows are subjected to high amplitude cyclic loading, the cross-section geometry distorts and bulges progressively with number of cycles, while the failure mechanism is largely associated with the initiation and propagation fatigue cracks. 11,18 The focus of the current study is the effect of the localised wall thinning on the low cycle fatigue resistance of elbows made of copper-nickel alloy.…”

“…In the case of extreme event (eg, earthquake or shut down), the piping elements are subjected to high amplitude loading excursions, leading to material cycling in low cycle fatigue regime . There were many analytical, numerical, and experimental studies in this area with the ultimate aim of developing a method for the evaluation of low fatigue strength of various piping elements with various wall thinning defects with and without internal pressure . For steel elbows, the recent studies have demonstrated that when the elbows are subjected to high amplitude cyclic loading, the cross‐section geometry distorts and bulges progressively with number of cycles, while the failure mechanism is largely associated with the initiation and propagation fatigue cracks …”