Simulation Of Thermo-hydraulic Forming Process For Bimetallic Composite Pipe

Bimetal composite pipe is widely used in oil and gas pipeline transportation because of its excellent characteristics of high pressure bearing and corrosion resistance.Thermo-hydraulic forming process has the characteristics of uniform pressure and easy forming.It can increase the bonding force between bimetal composite pipes and the forming pipe is suitable for high-temperature and complex environment.At present,the researches on thermo-hydroforming properties for bimetal composite pipe are mainly based on residual contact stress,while rebound,bulging coefficient and wall thickness reduction rate are also important parameters to evaluate the forming properties.In this paper,SA106-B/316 L bimetal composite pipe was taken as the research object,numerical simulation of its thermo-hydroforming process,and explored the influence of process parameters on the thermo-hydraulic forming properties(rebound,bulging coefficient,and wall thickness reduction rate)for bimetal composite pipe were carried out.The main research contents are as follows:(1)The thermo-hydraulic forming process for bimetal composite pipe was numerically simulated by ANSYS Workbench,and its result of residual contact stress under a given hydraulic expansion pressure is obtained.Compared the numerical simulation result with the experimental result and the analytical solution,the errors are all within the allowable range,which proves the validity of the built model.(2)The effects of process parameters(hydraulic expansion pressure,heating temperature,friction coefficient,outer tube wall thickness,inner tube wall thickness and initial gap)on the thermo-hydroforming properties(residual contact stress,rebound,bulging coefficient,outer tube wall thickness reduction rate and inner tube wall thickness reduction rate)of bimetal clad tube were studied.The results showed,with the increase of hydraulic expansion pressure,the residual contact stress,rebound,and bulging coefficient increase,the outer tube wall thickness reduction rate decreases,and the inner pipe wall thickness reduction rate remains basically unchanged;with the increase of heating temperature,the residual contact stress and bulging coefficient increase first and then decrease,the rebound increases,the outer pipe thickness reduction rate decreases first and then increases,and the inner pipe thickness reduction rate increases;with the increase of friction coefficient,the residual contact stress,rebound,bulging coefficient,outer tube reduction rate,and inner tube reduction rate have no obvious changes;as the outer tube wall thickness increases,the residual contact stress increases,the rebound,bulging coefficient,and the outer tube reduction rate decrease,and the inner tube wall thickness reduction rate increases first and then decreases;with the increase of inner tube wall thickness,the residual contact stress,the expansion coefficient and the reduction rate of the inner tube wall thickness all increase,but the rebound and the outer tube wall thickness reduction rate all decrease;with the increase of the initial gap,the residual contact stress,rebound,bulging coefficient,outer tube wall thickness reduction rate and inner tube wall thickness reduction rate shows a decreasing trend as a whole.(3)In order to optimize the thermal hydroforming process parameters for bimetal composite pipe,five process parameters of hydraulic expansion pressure,heating temperature,outer pipe wall thickness,inner pipe wall thickness,and initial gap,were selected as the test factors,four forming properties of residual contact stress,rebound,outer tube wall thickness reduction rate and inner tube reduction rate were selected as test indexes,and a five-factor three-level orthogonal test scheme was designed.Through range analysis and variance analysis,the order of the influence of process parameters on residual contact stress is: inner tube wall thickness > heating temperature > outer tube wall thickness > initial gap > hydraulic expansion pressure,all of which are highly significant;the degree on rebound is: inner tube wall thickness > heating temperature > outer tube wall thickness > hydraulic expansion pressure > initial gap,the inner tube wall thickness is a highly significant factor,the heating temperature is not significant,the hydraulic expansion pressure,outer tube wall thickness and initial gap have no effect;the order on outer tube wall thickness reduction rate is: outer tube wall thickness > initial gap > inner tube wall thickness >heating temperature > hydraulic expansion pressure,in which outer tube wall thickness and initial gap are the significant factors affecting the height,hydraulic expansion pressure,heating temperature and inner tube wall thickness have no effect;the order on inner pipe reduction rate is: outer tube wall thickness > heating temperature > inner tube wall thickness > hydraulic expansion pressure > initial gap,and all of them are very weak.The thermal hydroforming experiment for bimetallic composite pipe with the optimal combination of process parameters for residual contact stress was carried out.It can be seen that the inner-tube and outer-tube be well combined from the cross section and axial section of the thermal hydroformed composite pipe.The conclusions obtained in this paper will provide a certain reference value for the research of the thermal hydraulic forming process for bimetal composite pipe.