Research On Influence Of Water Depth On Welding Process And Quality Of Underwater Wet Welding

With the development of marine resources to the deeper and broader ocean areas and the increase of the service life of various assembly parts,the underwater welding repair work of offshore oil platforms,subsea pipelines and other underwater structures will increase gradually.Therefore,it is urgent to study the relevant technologies for deep water welding repair,which is of great economic significance and strategic significance for promoting the development of our marine industry.In this paper,the welding test within 100 m water depth is carried out on the self-constructed underwater wet welding experiment platform.The influence of water depth on the metal transfer characteristics is studied and its influence mechanism is explored.The fluctuation of arc voltage and welding current in different water depth is analyzed.The effect of water depth on the underwater wet weld quality is revealed to provide reliable theoretical basis and technical guarantee for the application of deep water wet welding.Firstly,the deep water wet welding experiment platform is constructed.The experiment platform includes X-ray high-speed imaging system,electrical signal acquisition system and high-pressure environment simulation system.The X-ray highspeed imaging system is used to observe the metal transfer in underwater wet welding,and the change of welding current and arc voltage is collected by electrical signal acquisition system.Through the X-ray high-speed imaging system,the metal transfer in different water depth is taken and the metal transfer mode is basically divided into two types: short circuit transfer and globular repelled transfer mode.When the welding parameters are constant,the droplet size and droplet transition period decrease with the increase of water depth.As the water depth increases,the angle of droplet deviating from the welding wire decreases,while the angle of droplet detachment increases generally.The diameter of bubbles decreases with the increase of water depth.The bubble rising velocity decreases at first and then increases with the increase of water depth.The influence of water depth on the stability of welding arc is studied by three indexes,U-I diagram,unstable combustion arc time ratio and variation coefficient.When the welding parameters are constant,the arc stability gradually becomes worse with the increase of water depth combining the three evaluation indexes.The macro forming,microstructure,mechanical properties and porosity of welded joints under different water depth is studied.The study shows that the weld formation gradually deteriorates,the continuity of the weld is reduced,and the defects such as spatter and under are increased with the increase of water depth.The depth-to-width ratio of the weld decreases at first and then increases.Porosity increases with the water depth increases.Increasing the wire feed speed or decreasing the welding speed will reduce porosity in weld metal.The content of ferrite(PF)in the weld decreases,the content of acicular ferrite(AF)increases,and martensite(M)begins to appear and gradually increases.The impact toughness and tensile strength of the weld decreases,while the average hardness of the weld increases with the increase of water depth.The arc stability model is established by the response surface method to analyze the influence of the water depth,voltage,wire feed speed and welding speed and the interaction between each other on the arc stability.Finally,the technological parameters conditions of underwater wet welding within 100 m water depth are obtained based on the established arc stability model.