The Influence Of Fluid Flow Characteristics On Electrochemical Reaction Process Of Metal Surface

In this paper,in order to discuss the influence factors of fluid-induced electrochemical corrosion,according to momentum,energy and mass conservation criteria,the Euler-Euler model was used to calculate the fluid flow parameters of the turbulent boundary layer near the pipe wall and the convection diffusion parameters of the electrochemical reactants.The relation between the surface electrochemical reaction rate and the liquid flow parameter is obtained according to the wall shear stress produced by the medium flow and the mass transfer coefficient of the electrochemical reactants in the boundary layer.At the same time,based on the theory of fluid mechanics and electrochemical corrosion theory,taking material of TP140and super 13Cr as the research material,the influence of fluid flow characteristics on the electrochemical reaction process of metal surface was studied by electrochemical methods in a self-designed jet experimental device.Using Sodium Chloride Solution as corrosion medium,and the flow velocity is in the range of 0²2m/s,three-electrode electrochemical test method was used to study the self-corrosion potentials and corrosion current densities of the two materials at different Cl^-concentrations and flow velocities.And experimental results are analyzed by electrochemical polarization method and electrochemical impedance spectroscopy.The simulation results show that in the flow environment,the velocity field,the energy field and the Cl^-concentration field of the liquid change are very greatly in the fluid boundary layer.The wall surface shear stress increases exponentially with the increase of the average flow velocity.The Cl^-mass transfer coefficient increases linearly with the increase of the flow rate in the liquid.The results show that in the static corrosion,whether it is TP140 steel or super 13Cr steel,the corrosion rate with the increase of Cl^-concentration presents a trend of rising first and then decreasing.The maximum corrosion rate of TP140 steel is 3wt%NaCl concentration,and the corrosion rate is 0.1396mm/a,which is about 8.21 times that of pure water medium.When the Na Cl concentration is close to 3.5wt%,the corrosion rate of the super 13Cr steel is maximal(1.88×10^-2mm/a).In the impact of high-velocity liquid,the corrosion rate of the two materials also has a maximum value with the change of flow velocity.The corrosion rate of the super 13Cr steel is 0.175 mm/a in 14m/s,while the critical velocity of the maximum corrosion rate 1.473mm/a of TP140 steel is 16m/s.Because of the dense oxide film on the surface of stainless steel,Super 13Cr steel is more resistant to oxygen corrosion than TP140 steel.In the flowing environment,the increase of the liquid flow velocity leads to the increase of the wall shear stress and the reaction mass transfer rate,which is the main reason for the increase of the wall electrochemical reaction rate.However,this promotion effect is very obvious at low flow velocities.Once the critical flow rate is reached,the increase of flow velocity will have an inhibitory effect on the corrosion reaction due to the influence of the mass transfer rate and the wall reaction process.