Corrosion Behavior Of Carbon Steel And Stainless Steel In Petrochemical Circulating Cooling Water

Corrosion is one of the main destructive factors in petrochemical industry.With the prolongation of service time of circulating water cooling equipment in domestic refineries,the corrosion leakage of circulating water cooling equipment and its pipelines is becoming more and more serious.In this paper,The corrosion behavior and mechanism of 20#carbon steel and 304 stainless steel in circulating cooling water of Jinling Petrochemical Company were studied in this paper.In order to provide a theoretical basis for the corrosion and protection of heat exchangers in petrochemical enterprises,the effects of p H value,flow rate,dissolved oxygen content and Cl~-concentration of circulating water on corrosion behavior of two kinds of steel in simulated circulating cooling water were studied by weightlessness method,electrochemical measurement technology,scanning electron microscopy and X-ray diffraction,the results show that:The corrosion type of 20#carbon steel in circulating water is uniform corrosion and pitting corrosion.When the p H of the solution is 6.4-9.5,the corrosion rate of 20#carbon steel decreases with the increase of p H,and the whole corrosion reaction is controlled by the cathodic reaction.When the p H of the solution is 7.2-8.4,the corrosion current density and the number of corrosion pits are almost the same;when the solution p H is 9.5,the maximum corrosion pit depth is only 55.14μm,and the number of corrosion pits is significantly reduced.When the solution flow rate is 0.6-1.5m/s,the corrosion rate of 20#steel increases significantly with the increase of flow rate,corrosion resistance is weakened,and the increase of flow rate can promote the cathode reaction of the electrode;when the flow rate is 1.5m/s,The corrosion current density is about 3 times that of static,and the surface of the sample after the polarization is Ulcer corrosion and speckle corrosion.When the Cl~-concentration is450-1000mg/L,the corrosion rate of 20#steel increases slightly with the increase of Cl~-concentration,and the number of corrosion pits increases.When the oxygen content is2.5-7.5mg/L,the corrosion rate and corrosion pit depth of 20#steel increase significantly with the increase of oxygen content,and the radius of the capacitive arc is obviously reduced.The cathodic reaction is greatly affected by the oxygen content.Pitting corrosion mainly occurs in 304 stainless steel in circulating water.When the solution p H is 6.4-9.5,with the increase of p H,the corrosion rate decreases,the pitting potential gradually moves forward and the pitting sensitivity decreases.When the solution p H is 6.4,the pitting factor is the maximum and the pitting density is 2.76/cm~2.When the concentration of Cl~-is 450-1000mg/L,the corrosion rate changes little with the increase of Cl~-concentration,the pitting potential decreases slightly,and the stability of passivation film decreases.When the flow rate is 0.6-1.5m/s,the corrosion rate increases with the increase of the flow rate,the pitting potential decreases,and the radius of the capacitive arc decreases significantly.When the oxygen content of the solution is 2.5-7.5mg/L,the corrosion rate,pitting density and pitting factor increase significantly with the increase of oxygen content.Finally,the regression curve of the corrosion model of the circulating water pipeline is obtained by fitting the least squares method,and the accuracy of the curve is verified by the agreement between the experimental data and the prediction curve.