石化循环冷却水pH值对20碳钢腐蚀行为的影响

Effects of pH Value on Corrosion Behavior of 20 Carbon Steel in Petrochemical Circulating Cooling Water

为探究石化循环冷却水pH对碳钢腐蚀行为的影响,利用动电位极化曲线、浸泡试验及交流阻抗技术对20碳钢在35℃、不同pH值的模拟石化循环冷却水中的腐蚀行为及机理进行了分析,并结合3D表面测量仪观察了试样表面的腐蚀形貌。结果表明:随着溶液pH值的增大,碳钢腐蚀整体呈减缓趋势;当pH=6.4时,金属表面腐蚀最为严重,点蚀和均匀腐蚀共存,最大蚀坑深度高达80.16μm,腐蚀产物膜完整性较差;当pH值为7.2~8.4时,各试样的腐蚀电流密度、蚀坑深度、电荷转移电阻值均相差不大,此区间pH值对腐蚀影响较小;当pH=9.5时,金属表面形成较为完整的腐蚀产物膜,最大蚀坑深度仅为47.88μm,腐蚀程度最轻。

In order to study the influence of pH value on the corrosion behavior of carbon steel in circulating cooling water of petrochemical industry,the corrosion behavior and mechanism of 20 carbon steel at 35℃in simulation circulating cooling water with various pH values were analyzed by potentiodynamic polarization curves,immersion test and electrochemical impedance spectroscopy.Meantime,the corrosion morphology of the samples was observed by 3D surface measuring instrument.Results showed that with the increase of solution pH value,the corrosion of carbon steel decreased as a whole.When the pH value was 6.4,the corrosion of metal surface was the worst,and both pitting corrosion and uniform corrosion co-existed.The maximum depth of corrosion pits was up to 80.16μm,and the integrality of corrosion product film performed worse.When the pH value was 7.2-8.4,the corrosion current density,corrosion pit depth and charge transfer resistance of each sample were not significantly different,and the influence of pH value on the corrosion was small in this range.Furthermore,when the pH value was 9.5,a relatively complete corrosion product film formed on the metal surface,and the maximum pit depth was only 47.88μm,which presented the lightest corrosion degree.