Research On Composite Forming Technology Of Nickel-based Bimetal Pipe Fittings

Owing to their outstanding properties of corrosion resistance,mechanical and processing performance,Nickel/L3 60 steel bi-metal composite pipes are becoming one of the most important pipeline transportation choices in bad oil and gas fields which have high levels of CO2,Cl-and H2S.But nowadays,scientific and systematic research of material properties and forming rules is still lacking.This paper used the method combining theories and experiments to compare various influence rules of pipe material under different heat treatment processes.What was more,finite element method was used to ensure parameters matching of composite pipe hydroforming process,which helped successfully,produce a large diameter nickel/L360 steel composite three-way pipe that meets the engineering requirements.Focusing on the influence of material properties under different heat treatment processes,OM,SEM,Vivtorinox hardness tester and universal testing machine were used to analysis the changes of sample microstructures and mechanical properties,which offered the judgments of best heat treatment process.The results show that:samples under 940? SSWC+520? tempering process,microstructures of which have completely transformed to tempered martensite on L360 steel part.Meanwhile,the nickel part has acquired obvious solid solution strengthening and has weakened the susceptibility of intergranular corrosion.Samples show the best interface bonding performance at this time.Finite element software ABAQUS was used to simulate the hydroforming process of nickel/L360 steel composite three-way pipe,which helped analysis the influence of forming limits with different parameters matching of axial feed,internal pressure and loading path,The results show that:under the process condition of 100MPa internal pressure,bilinear loading path and 0.06 friction coefficient,hydroforming performance achieves the best effect.Branch height gets the maximum value of 47.39mm when axial feed comes to 32mm and the outer pipe begins to rupture when axial feed comes to 32.7mm.On the base of cold extrusion process parameters acquired from simulation,thermoforming parameters under 940? annealing temperature were set to successfully produce a large diameter nickel/L360 steel composite three-way pipe,of which the branch height got about 80mm and the maximum thinning rate ?12%.No crack or interfacial separation was observed that made the pipe satisfied to practical engineering requirements.