Study On Welding Residual Stress Of Deep-sea Pipeline Steel

The exploitation and utilization of submarine mineral resources is an important strategic goal of China and a hot spot of global energy development strategy.The main difficulty in the development and utilization of seabed mineral resources lies in the development of mining and transportation machinery and equipment for mineral resources.As a typical pipeline lifting deep-sea mining system,deep-sea mining pipeline transportation plays an important role in the efficient and safe operation of deep-sea mining.The deep-sea mining straight pipe is faced with severe environment,such as ocean current load,dragging with surface ships and seabed mining vehicles,and seawater corrosion.All of these put forward higher requirements for raw materials of straight pipe.X80 pipeline steel has the advantages of high strength,good ductility and fracture resistance,and has great potential in the future marine steel.However,when the X80 pipeline steel is welded,a lot of residual stress will be produced in the component.Due to the harsh service environment of mining pipeline,the stress corrosion cracking caused by welding residual stress is easy to appear around the weld during the working process.In order to ensure the reliability and safety of deep-sea mining system,we must pay great attention to the quality of deep-sea mining straight pipe.Therefore,it is of great significance to study the distribution of welding residual stress and the influence of welding process on residual stress of X80 pipeline steel.This article systematically discussed the finite element analysis theory of the welding process,and used the finite element software ANSYS to modify the strain release coefficient in the blind hole method to measure the residual stress.Then,taking the welding residual stress of X80 pipeline steel as the research object,the thermal solid coupling calculation of X80 pipeline steel welding process was carried out on the basis of considering the phase transformation of metal.The simulation process was verified by infrared thermal imager,X-ray diffraction and blind hole method.Then,taking various welding parameters as variables,the residual stress changes of butt joint test plate and pipe under welding process parameters are studied.The results were as follows:(1)In this paper,ANSYS software was used to establish a three-dimensional finite element model to simulate the stress environment of blind hole in the stress release state of steel with different yield strength in blind hole method calibration test.And the strain release coefficient under different ratio of applied stress to yield strength of specimen was studied.According to the change law of elastic strain and plastic strain under different ? value,the change trend of strain release coefficient with ? value was analyzed.The distribution of the strain release coefficient of three different strain flakes with the change of ? value was discussed.Finally,the variation law of strain release coefficient with ? value was obtained by fitting,which would provide reference value for engineering application of blind hole method.(2)Based on the test of welding process by infrared thermal imager,the best heat source model was obtained.Combined with ANSYS software,the welding process of X80 steel butt joint test plate was calculated to obtain the distribution of welding residual stress.At the same time,the welding experiment was carried out,and the residual stress of the welding test plate was tested by X-ray diffraction method and blind hole method to verify the correctness of the calculation model.The effect of welding process on the residual stress of X80 pipeline steel butt joint test plate was studied.The results showed that the maximum welding equivalent residual stress appears at the center of the weld.With the increase of the distance from the weld center,the welding residual stress first increased and then decreased.The maximum welding residual stress decreased with the increase of welding speed,welding line energy and backing thickness.The maximum welding residual stress increased with the increase of plate thickness and groove angle.(3)Numerical calculations were carried out for the welding process of round pipes,and the residual stress after welding of the round pipes was tested by the blind hole method to verify the correctness of the calculation model.Subsequently,the research on the welding residual stress of X80 pipeline steel round pipes under different welding processes was carried out.The results showed that the maximum welding residual stresses on the inner and outer surfaces of the tube appear in the fusion zone.With the increase of the distance from the center of the weld,the residual stress of the round tube gradually tended to zero.The maximum residual stress decreased with the increase of welding speed and bottoming thickness,and increased with the increase of laminate thickness and groove angle.The welding process had basically the same influence on the residual stress of the tube and the plate.