Research On Hyperbaric GMAW Dcen Welding Process Of X70 Steel

China has a wealth of offshore oil and gas resources,including 24 billion tons of offshore oil and 140 trillion cubic meters of natural gas resources,development and utilization of these resources on the sustainable development of China's economy is of particular significance.A large number of marine engineering construction and submarine pipeline construction on the performance of submarine pipeline steel put forward higher requirements.In recent years,X70 high-strength steel is widely used in the construction of domestic submarine pipeline,and in-service X70 submarine pipeline steel maintenance,repair technology research less.Underwater high pressure dry GMAW welding technology is the ship,offshore platform,submarine pipeline and other underwater equipment maintenance key technology.In this paper,the X70 steel high pressure GMAW welding process is studied,and the high pressure GMAW welding process of X70 steel is studied by simulating 0.8-2MPa ambient pressure.According to the characteristics of hyperbaric GMAW welding process,reasonable experiment design and experimental study of welding in the flat,the polarity of the power supply and environmental pressure and the effects of welding parameters on welding process stability,droplet transfer and weld formation.The range of approximate technological parameters that can ensure the stability of welding process under different ambient pressure is obtained,and the influence of environmental pressure and process parameters on welding process is summarized,which provides guidance for high pressure GMAW welding of X70 steel.Considering the actual application scenarios of X70 submarine pipeline steel,combined with the characteristics of X70 pipeline steel welding under atmospheric pressure and multilayer multi pass welding,the multilayer multipass welding process of X70 steel was experimentally studied.The reasonable range of process parameters is calculated.On this basis,combined with the welding law of high pressure GMAW obtained from surfacing,X70 steel high pressure GMAW multilayer welding test is carried out.The macro metallographic,microstructure,hardness,impact work and tensile strength of the welded joint were analyzed and summarized.The X70 steel high voltage GMAW welding technology which meets the requirements was obtained.The existing welding process was optimized.The experimental results show that the GMAW welding process of X70 steel is different from that under normal pressure,and the range of process parameters for maintaining stable welding process is narrowed under high pressure.With the increase of environmental pressure,the transition form of droplet transition from short circuiting to repulsion transition gradually increases.Increasing the swing of welding gun can effectively reduce the welding leakage and undercut in welding process.The main structure of X70 steel weld joint of high-pressure GMAW welding for acicular ferrite,ferrite and a small amount of bainite,the hardness changes little;difference and mechanical especially microstructure and properties of heat affected zone,the overheated zone pearlite organization or finer martensite bainite thick.Under high pressure,the weld width is narrow,the penetration depth is deeper,the heat affected zone is coarse,the martensite number increases,and the impact energy decreases.The increase of welding voltage,wire feeding speed and welding speed can effectively improve the tensile strength,impact energy and hardness of welded joints.