Although the required minimum thickness (tsr) of T-joints (tees) of class 2, 3 and lower classes of nuclear power plants in Japan is calculated from the design pressure and temperature for design, there are neither any rules nor standards for thickness management of wall thinning T-joints for facilities maintenance.
This paper describes additional parametric study results and proposes a guideline for thickness management of wall thinning T-joints. In other papers related to this project, the experiment and numerical simulation results are reported. This paper refers to these results and performs further investigation under the consideration of JSME (The Japan Society of Mechanical Engineers) design, construction and maintenance codes and standards.
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.
In August 2004, a pipe rupture accident occurred at The Kansai Electric Power Company Mihama Unit3. Japan Society of Mechanical Engineers (JSME) recognized that it was an urgent problem to settle the rules on Pipe Wall Thinning Management by Fluid Flow. JSME enacted “rules on Pipe Wall Thinning” that stipulates the basic requirements of pipe wall thinning management, considering from these situations. In 2006, JSME enacted the “rules on Pipe Wall Thinning Management for PWR Power Plants” (JSME S NG1-2006, JSME rules for PWR) that satisfies the requirements of “rules on Pipe Wall Thinning”. This JSME rules for PWR stipulates the process of inspection plan, measurement, evaluation and maintenance. This paper focuses on the technical grounds that specify the management systems, pipe components and initial FAC rate.
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