Mechanics Analysis and Experimental Verification of Flange Joints in Piping Systems of Power Plant

Piping systems are used to carry gas and liquid medium, the pipes are often connected to each other by welding or flange joints in the same or different directions with fittings and valves, building up the piping systems. To make sure the piping system working properly, we should avoid the failure modes such as damage、leakage and so on happened, especially for those in the connected joints. Piping systems are usually used to transport the steam driving the turbine or the water in the cooling units. The Residual Heat Removal (RHR) piping system is one of the most important systems in a power plant, composed of heat exchangers 、valves and primary the piping systems. When the power plant is under emergency condition, the systems mentioned will supply the emergency cooling water to make sure the core components won’t be damaged due to high temperature. In order to avoid the failure modes such as damage、leakage, and so on happened, we should make sure the pipelines especially for those within the joint are strong enough to function normally under seismic condition. In this thesis, we study the loosening mechanism in the case of RHR-C loop in power plant, and focus on how the plastic deformation on the gasket will lead to loosening of the clamping force of the bolts. By setting the zero clamping force as the index of failure, discuss if the allowable moment of flange joints defined by ASME B&PV Code is applicable for this case. This study is divided into two parts. In the first part, we found that the leakage phenomenon happened in the quasi static test of RHR pipeline. Then, a simplified component test is going to examine all the components in the flange joint. After finding that the gasket is the most critical component by a comparison test, we study the mechanism between the deformation and loading on it. After then, by taking the experimental data into the FEM input and creating the numerical model of those pipeline in experiments. By comparing the FEM results and the experiment data measured, we can make sure that the deformation behavior of the gasket accounts for the loosening in clamping force of the bolts. We build the piping system taking the gasket behavior into account, and setting both static and dynamic analysis. By comparing the results of the analysis and experiment data, it is concluded that the analysis is fitting reasonably well. By the end of the study, we’ll make an analysis to predict if the ASME piping PV code is suitable for this case.