Investigation Of Mechanical Properties Of Bi-material Lined Pipe For Submarine Oil And Gas Transportation

The bi-material lined pipe is corrosion resistant and economical,therefore bi-material lined pipe is an effective solution in exploration of offshore corrosive oil.The mechanical bi-material lined pipe is tightly combined by a carbon steel outer pipe and a stainless-steel liner through a mechanical process.Thermo-hydraulic forming process can provide a more stable bonding force in producing mechanical bi-material lined pipe.The control of the residual contact stress in the thermo-hydraulic forming process was studied first,since the residual contact stress between the liner and the outer pipe is an important indicator of the functionality of bi-material lined pipe.The nonlinearity of the liner and outer pipe materials and the contact characteristics between the liner and outer pipe was considered in finite element model of the bimetal composite pipe to simulate the production process of heating,pressurizing,depressurizing and cooling stages of the thermo-hydraulic forming.Parameter sensitivity analyses for the thickness ratio between the liner and outer pipe,the initial radius difference of the inner and outer pipe,the heating temperature of the outer pipe,the hydraulic pressure and the contact heat conduction were carried out to study their influence on the contact pressure response and the stress-strain response of the liner in the thermo-hydraulic forming process.Results show that the heat conduction between liner and outer pipe has a significant impact on the circumferential stress-strain response of the liner.To increase the bonding force,the appropriate thickness of the liner should be selected through experiments.The initial radius difference should be reduced,and the heating temperature of the outer pipe and hydraulic pressure should be increased in productionSubmarine pipelines are faced with complex submarine terrain and environmental loads.The mechanical properties of bi-material lined pipe with thin liner and circumferential residual stress should be studied.Studying the mechanical properties of bi-material lined pipe is of great significance to ensure the safety of oil and gas transportation.The non-axisymmetric initial geometric defects of the liner were designed first.Based on the theory of axial compression buckling deformation of circular tube,fully considering the nonlinearity of the liner and outer pipe materials,finite elements models were built to simulate bi-material lined pipes with initial geometric defects under two loading processes of axial compression and bending after thermo-hydraulic forming process.The influence of the geometric characteristics of the initial defect on the compression and bending behavior of the bi-material lined pipe was studied.Later on,the compression and bending stress-strain response of the bi-material lined pipe under different circumferential residual stress,liner and outer pipe thickness ratio and relative internal pressure were studied.Results show that initial geometric defects reduce the axial compressive strength of the bi-material lined pipe.Larger circumferential residual compressive stress of the liner,proper internal pressure of the submarine pipeline and suitable thickness ratio of the liner and outer pipe can increase the separation resistance ability of the bi-material lined pipe.The bi-material lined pipe is prone to separation when it is partially bent.The existence of defects aggravates the separation under bending.Increasing the circumferential residual stress and the thickness of the outer pipe,and keeping the internal pressure greater than external pressure can enhance the local bending strength of bi-material lined pipe.