Experimental Study On The Dynamic Progression Of Erosion-corrosion Of X65 Pipeline Steel In Different Flow Environments

Metal components such as pipelines,valves,impellers and propellers are widely used in marine engineering,petrochemical and water conservancy industries.As they are often used in corrosive fluid containing solid particles,erosion-corrosion becomes one of the main failure forms of such metal component.X65 pipeline steel has the advantages of benifit mechanical properties and low cost,leading it to be widely used in the construction of oil and gas pipelines.However,the main microstructure of X65 pipeline steel is ferrite and pearlite.Thus in the environment containing corrosive media such asO₂,CO₂ andH₂ S,X65 steel pipeline is susceptible to corrosion damage,when the fluid contains solid particles.The synergistic effect between mechanical erosion and electrochemical corrosion will further lead to perforation,wall thinning and plastic deformation of the X65 steel pipe,which would result in the failure of the pipeline.Various researchers have studied the erosion-corrosion mechanism of X65 pipeline steel,however,the related researchs mainly focused on the coupling effect of mechanical erosion and electrochemical corrosion on X65 pipeline steel.Few researches were conducted on the dynamic progression of erosion-corrosion of X65 pipeline steel.Therefore,based on high-speed agitator,the dynamic progression of erosion-corrosion of X65 pipeline steel in different flow environments was studied using electrochemical impedance spectroscopy?EIS?and potentiodynamic polarization?PDP?measurement techniques.In combination with weight loss measurement and surface morphology observation,the Stern-Geary coefficient?the value of B?of flow environment was also fitted.The main content of this work is summarized as follows:?1?The mechanical erosion component,electrochemical corrosion component and total metal loss of X65 pipeline steel under different flow rates were measured by weight loss measurement,electrochemical impedance spectroscopy method and potentiodynamic polarization method,and the variation of mechanical erosion component,electrochemical corrosion component and total metal loss under different flow rates of X65 pipeline steel was obtained.?2?According to the polarization curves measurement results,the Stern-Geary coefficient under the flowing condition is fitted.The fitting results show that,with the increase of anodic polarization potential in the flow environment,the anodic dissolution of X65 pipeline steel would gradually transfer from the activation corrosion satisfying the Butler-Volmer equation to the diffusion control,resulting in the Stern-Geary coefficient in the flowing environment fitted by traditional Tafel extrapolation method to be higher than the true value,which leads to a higher calculated corrosion rate.In combination with the EIS measurements results and fitted results from the cathodic polarization curves which was obtained under the same experimental conditions,accurate Stern-Geary coefficient was determined around 30±2.4 mV.?3?Based on macroscopic morphologies and microscopic characteristics of X65 pipeline steel after erosion-corrosion,in combination with the kinetic reaction parameters under different flow rates,the dynamic progression of erosion-corrosion was discussed.When the corrosion process was under activation control,with the kinetic energy of the sand particles reaching the critical impact energy,the erosion-corrosion of X65 pipeline steel would occur.After the appearance of erosion,the surface morphology of X65 pipeline steel would changes from long and narrow"flow mark"corrosion morphology to the continuous impingement craters erosion-corrosion morphology.The observation results show that erosion-corrosion is a dynamic progression process controlled by the growth of the impact pits and the wear of the corrosion product layer.