Numerical simulation on temperature field and residual stress field in thermite welding of pipelines

Abstract

During the thermite welding of in-service oil pipelines, empirical values are often used for the dosage of aluminum powder welding flux, and the uncertainty of temperature and residual stress generated during the welding poses a serious threat to the construction of pipeline and its safe operation. In response to this problem, the thermite welding process of pipelines in different wall thickness and with different dosages of welding flux was analyzed with the numerical simulation software ANSYS.Specifically, a finite element model of thermite welding was established, and thus the change law of the temperature field and residual stress field with different dosages of aluminum powder welding flux and different pipeline wall thicknesses was obtained,which was also verified by test. As indicated by the results, the maximum temperature in the welding area of pipelines with same wall thickness rises with the increasing dosage of welding flux. The maximum temperature in the welding area decreases with the increasing of pipeline wall thickness in the case that equivalent welding flux is used. Besides, with the increasing of pipeline wall thickness, the maximum residue stress at the weld is up to 150 MPa, lower than the yield limit of material, so that no burn-through and crack will occur during thermite welding, and the simulation results are consistent with the test results. Moreover, it is safe and reliable to conduct thermite welding in 6 mm to 8 mm pipeline in service with 10 g to 20 g of aluminum powder. Generally, the numerical simulation method could provide reference for the safe operation of thermite welding of in-service pipelines, thus reducing the construction risks of pipelines in service.

Keywords

• pipelines
• thermite welding
• numerical simulation
• temperature field
• residual stress field