A Finite Element Analysis For Plastic Limit Load Of Welded Piping Branch Junctions

The branch junction is an important component in piping systems. Meanwhile, its rationality design and safety assessment, as an indispensable part of safeguard technology for piping systems, have drawn the attention of many researchers at home and abroad. But at all times the investigation of safety assessment technology for piping systems with defects has been limited to straight pipes, branch junctions with and without cracked flaws, excluding the locally-thinned piping tees; also the investigation of defect-free branch junctions hasn't made perfect at all. Considering the general failure mode of defected piping tees is plastic failure, the systematic analysis and the engineering calculation of the limit load for piping tees with and without defects become the key point of their integrality assessment technology. As a part of the National Tenth Five-year Science and Technology Research program, the plastic limit load for welded piping branch junctions, with and without locally-thinned defects, were studied in this paper, by means of finite element method and theoretical analysis. The main contents and achievements are as follows: Firstly, the three-dimension finite element models of defect-free and defected welded branch junctions under internal pressure were built, subsequently the most suitable numbers of the elements were presented for both of them. The plastic limit pressure database about branch junctions with and without defects were established, which in turn served as groundwork in the process of constructing the limit load estimation equations.The factors which have an effect on the limit pressure were simplified, and at the same time the influence of the defect sizes on the locally-thinned piping tees were investigated in detail.Eventually, the engineering estimation equations for limit load of both the defect-free and defected piping tees, under internal pressure, were created.