Numerical Simulation And Experimental Research On Hot-wire TIG Welding Of Bimetallic Composite Pipes

With the rapid development of industrialization,oil and natural gas are indispensable energy sources,and the acid medium such as CO₂and H₂S contained in oil and gas has more and more demand for pipes resistant to corrosion and low temperature,and bimetallic composite pipes.It not only satisfies the corrosion resistance,but also has a high pressure bearing capacity.It not only meets the safety requirements of oil and gas transportation,but also greatly reduces the cost.The manual welding has higher requirements for the staff and the operation difficulty.Large,this test uses a fully automatic hot wire TIG welded composite pipe,which will not increase the line energy,but also reduce the dilution rate of the elements.When the pipe is docked,the stress it receives is large,and it is inevitable that the wrong side will occur.As a result,the phenomenon of unmelting and unmelting occurs when the pipe is welded,and the performance of the welded joint is severely reduced.Therefore,the composite pipe of different misalignment amounts is welded to determine the misalignment range of the hot wire TIG welding.In this paper,the V-groove of composite pipe is taken as the experimental object,and the welding test system is built according to the different misalignment,and the numerical simulation is carried out by using the finite element analysis software.The physical properties of materials are greatly affected by temperature,so a double ellipsoidal heat source is used.The model conducts finite element analysis of the pipe’s staggered edges from the perspective of the welding temperature field,and compares the simulation with the test results.The results show that with the increase of the nozzle’s butt joints,the penetration depth and width of the tube are significantly increased.The difference is that the side wall of the nozzle is not on the same straight line,which causes the distribution of the welding temperature field to appear uneven,which further changes the penetration.The simulation result is that when the misalignment is less than 0.6mm,the penetration effect is good.When the side is larger than 0.8 mm,there is a phenomenon of incomplete penetration.The simulation results are verified experimentally.After the underwelding of the composite pipe is completed,the unmelted phenomenon occurs when the misalignment reaches 0.8mm.The temperature field will also have a certain effect on its penetration and width.In the case of a misaligned edge,the shape of the back weld is also different,but the unmelted side of the specimen with a misaligned edge less than or equal to 0.6 mm does not occur,so the test results are basically consistent with the simulation results.By using different flow rates N₂as the back substitute protective gas for testing,slagging occurs during welding.Its N₂should not be used as a back shield gas for nickel-based alloys.It is not suitable for 0.6mm off set side welds,heat affected zones,and The analysis of the microstructure of the base material area shows that the microstructure of the welded test piece is finer and more uniformly distributed in the case of misaligned edges.The mechanical properties tests were performed on the test pieces with different staggered edges,and the results showed that there was no significant difference in the performance of the test pieces with different staggered edges.Using msc.marc finite element software to analyze the residual stress of composite pipelines,the variation law of residual stress after welding was studied.X-ray diffraction method was used to detect the residual stress of the welded composite pipe after welding.The results were different to some extent,but the stress distribution was basically the same,which could verify the accuracy of the test.