Study On Corrosion Behavior Of Drill Pipe In Mud Environment

With the development of oil and gas exploration and the improvement of technical requirements,the drilling environment is becoming increasingly complex.During the drilling process,in order to meet the requirements of the drilling process,various drilling fluid systems such as salt water and sodium based polymers need to be used,which contain various mud additives and have severe corrosion effects in the downhole environment.Therefore,corrosion is one of the important factors that cause damage to drilling tools.Petroleum drill pipe is the main component of drilling tools used in oil and gas well drilling.It is a rod used to connect the drill bit,transmit torque,and weight on bit.Due to differences in the composition and physical properties of materials,the magnitude and distribution of residual stress generated by drill pipe welding will significantly change,which will directly affect the corrosion resistance of the workpiece,thereby limiting the further use of drill pipes.Therefore,studying the distribution of residual stress in drill pipe welding and its impact on corrosion performance is of great significance for ensuring the safety and reliability of welded structures.Aiming at the corrosion behavior of drill pipe in mud environment,this paper uses finite element simulation method to study the welding process of drill pipe,and verifies it through experiments.The effect of corrosion on the corrosion resistance and mechanical properties of drill pipes was studied.Combined with the results of corrosion experiments,the stress corrosion law of drill pipes was studied.The specific work and conclusions of this paper are as follows:(1)A thermo-mechanical coupled finite element model of drill pipe was established using Deform,and the temperature field,stress/strain field,and axial shortening during the welding process were obtained.The effects of rotational speed,axial force,and rotational inertia on the maximum temperature,axial shortening,and welding residual stress during the welding process were studied using a single factor variable analysis method,and reasonable welding process parameters were determined.(2)The numerical simulation of the inertial friction welding process is verified through actual welding experiments.The experimental results are in good agreement with the simulation results,verifying the reliability of the simulation.Mud corrosion weightlessness experiments were conducted on drill pipes to study the corrosion resistance under different welding process parameters.The results showed that with the increase of rotational speed,the corrosion rate first decreased and then increased;Through mechanical tensile testing experiments,it can be seen that corrosion reduces the mechanical properties of drill pipes.(3)Considering the deformation of drill pipe under tensile load,a finite element model of stress corrosion of drill pipe containing residual stress was established using Comsol.The Mises stress,corrosion potential,and corrosion current density of the part of drill pipe subjected to residual stress were studied,and the effects of defects,different influence ranges,and defect depths on stress corrosion were analyzed.The results show that when there are no defects on the surface,the stress corrosion can be slowed down with the increase of the influence range;When there are defects on the surface,the stress corrosion behavior of the central part of the defect will become more serious as the depth of the defect increases,which is prone to lead to pitting corrosion of the drill pipe.