Thermomechanical analisys of in-service welding pipelines using the element-based finite volume method

Abstract

Currently, the welding process is the most used technique for joining workpieces. In-service welding of oil and gas pipelines is a technique, which shows important economic aspects as well as low environmental impact. The aforementioned benefits are possible since there is no need for interrupting the flow operation during pipe repairs, branch on pipes or substitution of some defective pipe section. However, during this process, some detrimental phenomena such as hydrogen-induced cracking and burn-through may appear. The thermomechanical model for analyzing heat transfer from the arc welding as well as the fluid flow into the pipeline is very complex, therefore analytical solutions are not available. Physical studies might present many difficulties for analyzing the process. Therefore, numerical methods emerge as an attractive alternative to solve several classes of engineering problems. The main goal of the present study is to develop a numerical simulator using the EbFVM (Element-based Finite Volume Method) to analyze in-service welding processes of pipelines. The flexibility of treating complex geometries through EbFVM make possible the analysis of various actual engineering problems. Based on the performed simulations, some preliminary modifications in the process variables can be proposed in order to improve the weld quality. For solving the governing equations arising from the thermomechanical model, the EbFVM was used in conjunction with unstructured grids. The numerical simulations were performed for applications in real welding process. Simulations were performed using methane as working fluid for a turbulent flow; Turbulence modeling was performed by making use of empirical correlation. The results are presented in terms of thermal cycles, temperature fields, axial and hoop stresses, and radial shrinkage, which evaluated them qualitatively and quantitatively. Furthermore, the developed simulator was confronted against experimental works, analytical solutions from literature, and others numerical studies. Finally, in most scenarios, excellent agreements were achieved.