Mechanical Analysis And Finite Element Simulation Study On Hydro-bulging Process Of Bimetallic Clad Pipe

Higher demands for the strength,corrosion resistance and high temperature resistance are put forward to the pipelines because of the diversification of the transport mediums and the complication of the transportation environments.Bimetallic clad pipes manufactured by the hydro-bulging technique have advantages such as good mechanical property and excellent corrosion resistance,moreover,they also have advantages in improving the quality and productivity of products.The bulging pressure can be calculated accurately by the geometric and mechanical parameters of the base pipe and liner pipe.The bimetal clad pipe manufactured by the hydro-bulging process has no scratches or damages on the inner surface and the wall thickness is uniform,so it has great development potential and gains extensive attention of the researchers and manufacturers.However,there are many factors influencing the hydroforming of composite pipe.If the process parameters are selected improperly,problems such as insufficient bonding strength,bulge instability and expansion crack are often caused in engineering practice,which directly affects the accurate realization of hydroforming and the improvement of product quality of bimetallic clad pipe.The traditional method of trial-produce bimetallic clad pipe for many times will increase the improvement cycle,waste human,material and financial resources,and lead to the increase of production cost.In this paper,the hydroforming process of X70/316 L bimetallic clad pipe is studied systematically and deeply by combining theoretical research method and finite element simulation method.The main research and results are as follows:A calculation method of liner pipe's equivalent yield strength is improved.Base on the displacement compatibility condition and the plane strain hypothesis,the relationship between residual contact pressure and bulging pressure are established.In addition,the ranges of the bulging pressure when the base pipe only produces elastic deformation and when the base pipe produces tiny plastic deformation are determined,and the theoretical analysis is verified.The finite element model of the hydroforming process of bimetallic clad pipe is established.Based on the model,the influence of forming parameters on the forming performance of the pipe is revealed.It is found that with the increase of bulging pressure,the hoop recovery of the inner surface of liner pipe decreases slightly,while the hoop recovery of base pipe increases gradually.The rise rate of rebound before plastic deformation of the inner surface of base pipe is greater than that after plastic deformation.The residual contact pressure between the inner surface of base pipe and the outer surface of liner pipe increases linearly.With the increase of the initial clearance,the difference between the elastic recovery of the inner surface of base pipe and the outer surface of liner pipe decreases gradually,and the residual contact pressure between the two pipes decreases gradually.With the increase of the liner pipe's thickness,the difference between the elastic recovery of the inner surface of base pipe and the outer surface of liner pipe decreases slightly,and the residual contact pressure between the two pipes increases slightly.The friction condition between the base pipe and liner pipe has little effect on the deformation,rebound and residual contact pressure of the bimetallic clad pipe.The paper selects the residual contact pressure and the elastic recovery as test indexes,and selects bulging pressure,initial clearance,liner pipe's thickness as three test factors.The results show that the important order that the factors affecting the index(residual contact stress)is bulging pressure,liner pipe's thickness,initial clearance;and the important order that the factors affecting the index(the elastic recovery)is bulging pressure,initial clearance and the liner pipe's thickness.Finally,in comprehensive consideration of the residual contact pressure and the elastic recovery,the optimal processing parameters are set as: the bulging pressure is 170 MPa,the initial clearance is 2mm,and the liner pipe's thickness is 3mm.