| The high-speed liquid-solid two-phase flow fluid in the tube will cause the interaction of the tube wall between particle impingement erosion damage and the flow liquid corrosion damage.The influence of the erosion and corrosion causes material loss,wall thickness reduction,perforation,and failure of the tube.Among them,the corrosion reaction is affected by particle erosion through boundary layer disturbance and wall surface modification,while the particle erosion process is also affected by the structural changes of corrosion on the tube wall.To study the erosion and corrosion interaction damage of high-speed liquid-solid two-phase flow on the tube wall for 304 stainless steel and P110 carbon steel,the electrochemical corrosion characteristics of liquid flow in the metal tube,the electrochemical response characteristics of single particle and multi-particle impingement on the electrode surface and the influence of electrochemical corrosion on particle erosion are studied respectively.Firstly,according to the development process of tube wall damage,this work started with the electrochemical corrosion of the tube wall by the flowing liquid,and the influence of flow velocity and reactant concentration on corrosion and passivation is discussed.According to the law of conservation of mass,a prediction model for the electrochemical corrosion of the flowing medium tube wall is established.Secondly,the current density transient response characteristics are tested by the step experiment of single particle and multiple particles impinging the electrode surface,and the current density transient response model is established.Thirdly,the calculation model of crevice corrosion is established,the experiment of the influence of electrochemical corrosion on particle erosion is carried out,and the process of corrosion promoting erosion is discussed.Through the above experimental measurement,the interaction between erosion and corrosion is quantitatively analyzed.The main research results are as follows:(1)Through the self-made small three-electrode measuring device,the influence of the sample on the flow near the tube wall is reduced and the reliability of the test is improved.Experimental results show that,when the flow rate is close to 9 m/s in the 3.5 wt%Na Cl pipe flow solution,the pitting corrosion of 304 stainless steel is the most serious;the average corrosion rate of the P110 carbon steel surface continues to increase with the flow velocity.The presence of Na Cl in the liquid makes the sample surface of 304 passivate obviously,the passivation range under 9 m/s is shorter,and the reaction is relatively violent.At the same time,the increase of the flow rate increases the pitting corrosion on the surface of 304 stainless steel.No obvious passivation occurred on the P110 sample surface,and the overall corrosion rate is greater than that of 304.Based on the theory of convection,diffusion and migration,a dynamic electrochemical corrosion calculation model of the tube wall is established.(2)The effect of erosion on corrosion is obtained by using the particle impinging surface experiment.The electrode surface parameters undergo a step after being impinged by particles,and then the current density returns to near the initial value nonlinearly.With the increase of single particle diameter and impinging velocity,the current density peak value of 304 stainless steel and P110 carbon steel electrode surface increases.At the same time,it takes longer for the current density to recover from the peak value to close to the initial value.When multiple particles continue to impinge the tube wall,the anode current density fluctuates violently,which accelerates the dissolution of the material.According to the different response process of current density,a model of the current density transient of particles impinging the electrode surface is established.(3)Gas-solid and liquid-solid two-phase flow experiments show that corrosion promotes the particle erosion of 304 stainless steel and P110 carbon steel.The maximum increase percentage of P110 is 193.38%,while the increase of 304 is smaller(11.68%to 36.68%).The promotion effect is greatly increased after the strong electrolyte Na Cl is added to solution.When the Cl~-concentration is increased up to 3.5 wt%,the erosion rate of P110 increases nearly 8times.According to the lips formed on the surface crater under the impingement of particles,the deformation of the root of lips and the propagation rate of the crevice caused by corrosion are calculated,and the crevice corrosion promotes particle erosion model is established.It theoretically supports the phenomenon that corrosion promotes particle erosion in the experiment.(4)The quantitative analysis of the interaction shows that the corrosion rate increase percentage of 304 stainless steel in the liquid-solid two-phase flow is greater than that of the erosion rate,and the erosion rate of P110 carbon steel increases more obviously.The effect of particle erosion on corrosion is more obvious in liquid-solid two-phase flow,and the interaction damage shows a positive synergistic effect. |
PDF Full Text Request