| The polar condensate tanker is an indispensable tool for the exploitation of polar resources and it plays an important strategic role.The heating coil is an important equipment for the polar condensate tanker.Its construction requires the application of all-position automatic TIG welding technology.At present,the domestic all-position welding technology and equipment are still immature,so the development of advanced pipeline all-position automatic TIG welding technology and equipment are significant.The material of the polar condensate tanker heating coil is BFe10-1-1 copper-nickel alloy,which has good weldability,good mechanical properties and corrosion resistance.In this paper,the research on all-position automatic TIG welding technology of copper-nickel alloy tube has important research significance and practical application value.When the heating coil is used for overhead welding and vertical welding,the molten pool is subjected to gravity,and it is difficult to control the weld formation.Therefore,different welding parameters were set at different welding positions,and the welding head needs further optimized according to the characteristics of the heating coil lap welding.So it can compensate the influence of gravity on the molten pool and realize all-position automatic TIG welding.In this paper,an all-position automatic TIG welding system for heating coils was built.The structure of the welding head was optimized and the functions of welding gun angle adjustment,visual monitoring and wire feeding attitude adjustment were realized,which can meet the requirement of automatic TIG lap welding of pipelines.This paper also studies the stress of the molten pool at different welding positions,and gives the conditions for the force balance of the molten pool.The influence of welding parameters on the formation of lap welds during flat welding was studied by the control variable method.The test results showed that peak current,arc voltage,welding speed,pulse duty cycle,pulse frequency and welding position had great influence on weld formation;base current had a little effect on weld formation.The all-position automatic TIG welding lap test of the pipeline based on the response surface method,which takes the peak current,welding speed,pulse duty ratio and welding position as input parameters,and takes the weld width,penetration and thickness as response.According to the experimental results,the mathematical model of response surface of weld formation was established.The influence of single factor and two-factor interaction on weld formation was analyzed.The optimization criteria of weld formation size were set and the welding parameters and weld forming dimensions at special welding position was optimized.In this paper,the influence of pulse frequency on the microstructure and properties of lap joints is studied.The results show that the pulse frequency has a significant effect on the microstructure and properties of lap joints.In this paper,the TIG butt welding of filler wire and unfilled wire were carried out,and the microstructure,grain size distribution,grain orientation and misorientation angle distribution of both the two butt joints were tested.The results show that: 1)Both area of the two butt joints are in a single α phase,the parent metal and the heat affected zone are equiaxed crystal,and the weld metal area is dendritic crystal.2)The grain size relationship of both area of the two butt joints is: base metal <heat affected zone < weld metal area.3)The grain orientation of the base metal is <111>,the grain orientation of the heat affected zone is between <111> and <001>,and the grain orientation of the weld metal area of the unfilled wire is <001>,which is obvious preferred orientation,while the grain orientation of the weld metal area of the filler wire is disappear.4)During the welding process,the Σ3 CSL grain boundary of the weld metal area is continuously reduced,and the high-angle grain boundary is continuously converted to the small-angle grain boundary. |
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