Although the reinforcement for openings is checked in accordance with design / construction standard when thinning was observed in T-pipes, this evaluation becomes too conservative or requires much time and effort.This paper describes additional parametric study results and proposes a guideline for thickness management of wall thinning T-pipes. On the other papers related to this project, the experiment and numerical simulation results are reported. This paper referred these results and performed further investigation. INTRODUCTIONThe working group that studies management of wall thinning of branch pipe connections has been established in Japan. This group consists of 11 Japanese electric power companies, 1 research institute, and 3 nuclear plant fabricators. This project performed burst experimental tests for T-joints (Tees) mock-ups [1] , FE analyses for the T-joints mock-ups [2] , evaluation of external pressure for T-joints [3] and developed a guideline for management of wall thinning of tees [4] . Also this project studied T-pipes (welding Tbranch connection) by an experimental mock-up test and FE analysis [5] and the management of wall thinning of the T-pipes (branch connection).This paper explains the proposals of wall thickness management criteria of T-pipes. When the wall thinning was observed in T-pipes, reinforcement for openings based on reduced thickness is checked in accordance with existing Japanese design / construction standard [6] . However, this evaluation becomes too conservative and requires much time and effort. Therefore, rational criteria of wall thickness management for T-pipes were desired.
Although the allowable external pressure for branch pipe connections is estimated by evaluation procedure for straight pipe, the applicability of procedure for straight pipe to branch pipe connections has not been clear. The applicability of evaluation procedure for straight pipe to branch pipe connections regarding to evaluation of allowable external pressure evaluation was discussed in this study. The buckling pressure of branch pipe connections was estimated by linear eigenvalue analysis with FEA (Finite Element Analysis). The types of branch pipe connections were T-joints and T-pipes. The range of configurations in branch pipe connections for FEA, such as ratio of outer diameter in main to branch pipe D/d and ratio of outer diameter to thickness in main pipe D/T, were determined by survey of branch pipe connections in the Japanese nuclear power plants. The results of the FEA showed that the buckling strength of branch pipe was found sufficiently to be superior than that of straight piping from comparisons of estimations by FEA for branch pipe connections and those by formula for straight pipe in the design code. It was concluded that the formula for straight pipe is applicable for the evaluation of allowable external pressure for branch pipe connections.
T-pipe is one of the typical structural elements of LWR piping as well as T-joint. In the present situation, the evaluation of wall thinning for T-pipe is accomplished by assuring the sufficient strength around the opening area by using the design and construction code. This evaluation often assumes the replacement of a local wall thinning with a global wall thinning, which leads to excessively conservative prediction of burst pressures. In this study, three-dimensional finite element analysis was conducted to simulate the fracture behavior of a pressurized T-pipe test. The accuracy of the predicted burst pressures and appropriate modeling of the welded joint at the junction of the main and branch pipes were investigated. It was found that the burst pressure could be adequately predicted by applying a proper fracture criterion.
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