Analysis And Prediction Of Electrochemical Corrosion Characteristics Of Tube Wall In The High Flowing Speed

Flow corrosion is one of the main causes of tube and equipment wall thickness thinning,bearing capacity reduction,corrosion perforation and fracture failure in oil and gas production,water conservancy and hydropower,metallurgy and other industries.It not only causing economic losses,but also cause the waste of energy and environmental pollution.In this thesis,the electrochemical corrosion behavior of P110 steel and 304 stainless steel in solution was studied by using the wall electrochemical test method in flowing solution.The results provide a basis for evaluating the service life of the tube.In this study,the corrosion behavior of carbon steel and stainless steel in six different fluid flow rates,four different concentrations of NaCl solutions and three different test tube diameters was studied by using tube flow test device and electrochemical workstation for online electrochemical test.The main conclusions drawn from the above research are as follows:(1)The corrosion rate of P110 steel increases with flow rate,while the corrosion rate of 304 stainless steel reaches the maximum value at 9 m/s.When the flow rate increases,the corrosive medium and the charge transfer will be changed,and the corrosion rate will be increased.At the same time,the flow rate will affect the structure of the corrosion product film on the material surface and the corrosion reaction.The synergistic effect of the two makes the flow rate change an important factor affecting the corrosion rate of materials.The anodic polarization curve of P110 steel shows the characteristics of dissolution,and the cathodic polarization curve is controlled by oxygen diffusion.The self-corrosion current density increases with the increase of flow rate,and the radius of capacitive reactance arc and charge transfer resistance decrease continuously.The integrity and protection of the corrosion product film decrease,indicating that the increase of flow rate accelerates the flow corrosion of P110 steel.The anodic polarization curve of 304 stainless steel shows passivation characteristics.In the range of 1 m/s to 9 m/s,the self-corrosion current density increases,the radius of capacitive reactance arc decreases,and the passivation film is destroyed,the flow rate plays a role in accelerating the corrosion.When the flow rate increases to 11 m/s,it shows that the self-corrosion current density decreases,the capacitive arc radius increases,and the low rate plays a role in inhibiting corrosion.(2)The corrosion rates of P110 steel and 304 stainless steel increase with the rise of the concentration of the flowing NaCl solution.The radius of Cl-in the NaCl solution is small,and the adsorption force is strong,which is easy to destroy the corrosion product film Therefore,when the Cl-concentration increased gradually,the corrosion product film formed on the material surface was destroyed,and the corrosion rate increased.The self-corrosion current density of P110 steel increases with the rise of solution concentration,and the radius of capacitive reactance arc and charge transfer resistance decrease.It shows that the increase of NaCl solution concentration promotes the corrosion reaction of P110 steel.When the solution concentration increases,the self-corrosion current density of 304 stainless steel rise,the radius of capacitive reactance arc decreases,and the tendency of corrosion reaction increases(3)At the flow rate of 3 m/s,when the tube diameter increases,the corrosion rate of P110 steel in NaCl solution rise,and the corrosion rate of 304 stainless steel increases first and then decreases.The corrosion rate of 304 stainless steel is the highest when the tube diameter is 15 mm.The change of tube diameter affects the fluid state flowing through the tube flow test section,which changes the compactness of the corrosion product film on the material surface and further affects the corrosion reaction rate.The self-corrosion current density of P110 steel showed an upward trend with the increase of tube diameter,and the capacitive arc radius and charge transfer resistance decreased.The compactness of corrosion product film decreased,and the corrosion reaction was more likely to occur.The self-corrosion current density of 304 stainless steel increases first and then decreases,the capacitive arc radius and the resistance of passive film decrease first and then increase.The corrosion of passive film with poor compactness is most likely to occur when the tube diameter is 15 mm,and the corrosion reaction is slow when the tube diameter is 20 mm.