Research On Corrosion Behaviors Of Rusted Carbon Steel And Countermeasures In Re-circulating Cooling Water

Rust/metal structure is one of the multiphase and multiple interface complex systems.The corrosion under rust is the uppermost and longest form of metalliccorrosion evolution.The paper used rusted carbon steel witch can more close to the real state of carbon steel in re-circulating cooling Water.In this paper,weight-loss measurement.electrochemical methods(polarization curves(PC)and electrochemical impedance spectra technique(EIS))?SEM and IR were employed to study the corrosion behaviour of carbon steel in circulating cooling water,analyze the influence of different factors on the corrosion behaviour of rusted carbon steel,study the morphologies,structures,compositions of rust layers,study the efficiency of the corrosion inhibitor under the condition of without cleaning and prefilming.The results show that:Under the different conditions of circulating cooling water,the corrosion rate of carbon steel have the same degressive trend with time:During the initial inunersion period,corrosive medium have a great effect on the carbon steel corrosion,the corrosion rate of carbon steel faster and reduced quickly.With the extension of corrosion time,the effect of the corrosive mediumweakens gradually.The decreasing trend of corrosion rate became slower and finally level off with the same corrosion rate.It instructions that corrosion products have a certain protective action on the rusted carbon steel,when corrosion reached certain level,the corrosion rate is no longer affected by the corrosive medium.Electrochemical tests show that the cathode reaction of carbon steel electrode was effected by rust layer;Icorr decreased with the extension of corrosion time;Rp increased with the extension of corrosion time;Yodecreased with the extension of corrosion time and was far less than the Yo value of dissolved oxygen in the rust layer,show that rust layer can suppress the diffusion of dissolved oxygen.SEM and IR show that rust layer appear stratification,the outer rust layer with a loose andporous structure,the main component is ?-FeOOH and ?-FeOOH.The density of the inter rust layer formed by little ?-FeOOH and Fe3O4,because of ?-FeOOH with high electrochemical activity,which leads to increasing the cathodic reaction rate than weight loss measurement.Fe3O4 slowly generated show that it is produced under the hypoxia conditions.The result shows that the rust layer can not only hinder the ions into the surface of carbon steel,but also can inhibit the diffusion of Oxygen.The results indicated that DJ-NPOland DJ-304showed a strong synergistic effect for the rusted carbon steel.The inhibition efficiency appeared to increase with increasing the inhibitors concentration and the ideal dosage of two inhibitors was 200mg/L when the inhibition efficiency,chemical cost and environmental protection were taken into account,and two kinds of corrosion inhibitor corrosion rate achieves above 70%.