Study On The Corrosion Mechanisms Of J55 Grade Steel At Different Flow Speeds In Mimic Sea Water

Regarded J55 grade steel as backing material, study on the flow speeds enhance the corrosion mechanisms of J55 grade steel in mimic sea water.Find out the influence to the corrosion process which by the flow speed of the solution. The corrosion performance of J55 grade steel in solution with different flow velocities is studied by using electrochemical methods such as potentiodynamic polarization curve, electrochemical impedance spectroscopy, etc as well as immersion test.To provide the basis evaluation for the corrosion of J55 casing material in the flow solution.The electrochemical test results show that:when the flow speed in the range of 0~1m/s,as the flow speed raise which in mimic sea water,itwill make the rate of the cath ode reaction increased.The open circuit potential and corrosion potential shifted positive ly,and the corrosion current density increased,also the polarization resistance of the elec tric double layer decreases.On the other hand,the accelerated of the cathode reaction wi ll lead to accelerated the anodic reaction at the same time,which will resulting in corro sion intensifies in the final. Flow speed has no effect on the J55 grade steel mechanismof the anodic reaction in the corrosion process,but it will increase the constant value of cathode Tafel and also increases the value of Tafel slope for the cathodic reaction.At the same time,with the increase of flow speed in the solution,the corrosion current density also increased significantly,which accelerates the corrosion process.The flow speed of the solution also reduces the polarization resisitance of J55 grade steel. Meanwhile the charge transfer resistance Rct decreases,and the Qdl increases.The flow speed mainly increase in double layer capactitance value, reducing the resistance values of the double layer. The corrosion product layer in the flow solution is smaller than in the static solution, it means that flow speed can promote the corrosion products leave from the surface of the specimen, which it will have a lower value of fR.The corrosion weight loss test show the results that :compared with the static solution,in dynamic corrosion conditions,J55 grade steel have pitting corrosion,the corrosion rate is the serious corrosion level,as the flow speed increasing,it will greatly promoted the coeeosion process.At the same time,because the flow speed increased the concentration gradient,so the J55 grade steel will has higher corrosion currentdensity and corrosion rate.The analysis of corrosion mechanism shows that: to improve the solution flow spe ed, accelerate the oxygen diffusion to the specimen surface in the solution, the cathodereac tion rate increases, accelerated thecathodic reaction process of steel surface, at the same ti me, the cathode reaction speed will lead to accelerated the anodic reaction, resulting in co rrosion intensifies in the final. To accelerate the flow of the solution not only improves t he uniform corrosion rate of J55 carbon steel,but also promotes cathode iontransferand d emotes the resistance of corrosion product.