X80钢在红壤模拟液及薄液膜中的电化学行为研究

发布时间：2018-05-13 11:46

本文选题：X80钢 + SO_4~(2?)　；参考：《南昌航空大学》2017年硕士论文

【摘要】：“西气东输”管线约1/5跨越酸性红壤区域,X80管线钢在红壤环境中的腐蚀失效是影响其使用寿命、使用安全的重要问题。目前,关于管线钢红壤腐蚀的环境因素,如腐蚀性离子的作用、腐蚀产物膜的影响及涂层破裂时液膜下的腐蚀行为,均尚无深入研究。因此,研究管线钢在不同条件的红壤模拟液及薄液膜中的腐蚀行为十分必要。本文通过动电位极化法、电化学阻抗谱、三维视频显微镜、扫描电子显微镜(SEM)等手段研究了土壤中腐蚀性离子SO_4~(2-)的含量、腐蚀产物膜对X80钢在红壤模拟溶液中腐蚀行为的影响,同时,探讨了涂层破裂下红壤模拟液膜pH值对X80钢电化学腐蚀的作用。研究结果表明,在酸性红壤模拟溶液中,X80钢的腐蚀速率随SO_4~(2-)浓度变化而明显变化;在含1%~5%SO_4~(2-)的模拟液中,SO_4~(2-)会阻碍腐蚀性离子Cl-在电极表面的吸附,从而减缓腐蚀,此时X80钢的腐蚀速率随SO_4~(2-)浓度增加而减小;当SO_4~(2-)质量分数大于5%后,高浓度的SO_4~(2-)会破坏电极表面膜的形成,此时腐蚀速率随SO_4~(2-)浓度升高而增加。在含1%~10%SO_4~(2-)的酸性红壤模拟液中,X80钢的EIS均呈现出高频容抗弧和低频感抗弧。由腐蚀失重量及腐蚀极化曲线分析可知,腐蚀产物膜的厚度与结构对X80钢的腐蚀速率有显著影响。当X80钢在红壤模拟液中浸泡4d时电极表面形成了较为完整的初期腐蚀产物膜,该产物膜具有保护性,此时腐蚀速率最低。随着浸泡时间增加,X80钢表面覆有中期腐蚀产物膜,产物膜分为内外两层,外层产物膜疏松呈暗黄色,内层较薄呈黑色;此时腐蚀产物膜保护性很差,腐蚀速率出现较大幅度的上升。当浸泡时间为30d时,试样表面覆有后期腐蚀产物膜,膜层厚度有所增加,产物膜更加疏松多孔,溶液中的腐蚀性离子容易进入金属基体表面与之发生反应,使腐蚀速率加快,此时腐蚀产物膜保护性较弱。结合不同厚度、不同pH值的红壤模拟液膜下X80钢的腐蚀电化学数据及腐蚀形貌分析表明,液膜厚度为80μm、pH=4时,X80钢腐蚀受腐蚀产物膜及氧气扩散的共同影响,X80钢腐蚀速率最小;pH值升至5~7时,氧还原控制腐蚀过程,X80钢的腐蚀速率小幅增加。液膜厚度继续增加后,即厚度为110μm、280μm、1000μm时,X80钢的腐蚀速率随着pH值的增大而减小,此与在本体溶液中所得结果相一致。
[Abstract]:The corrosion failure of X80 pipeline steel in red soil environment is an important problem affecting its service life and safety. At present, the environmental factors of pipeline steel red soil corrosion, such as the effect of corrosive ions, the effect of corrosion product film and the corrosion behavior under the liquid film when the coating is ruptured, have not been thoroughly studied. Therefore, it is necessary to study the corrosion behavior of pipeline steel in red soil simulated liquid and thin liquid film under different conditions. By means of potentiodynamic polarization, electrochemical impedance spectroscopy, 3D video microscope, scanning electron microscope (SEM) and so on, the content of corrosive ion so _ 4H _ 2O _ 2-in soil and the effect of corrosion product film on corrosion behavior of X80 steel in simulated solution of red soil were studied in this paper. At the same time, the effect of pH value of simulated liquid film on the electrochemical corrosion of X80 steel was studied. The results show that the corrosion rate of X80 steel varies significantly with the concentration of so _ 4 ~ (2) in the simulated solution of acidic red soil, and that in the simulated solution containing 1 ~ (5) so _ (4) ~ (2), it will hinder the adsorption of corrosive ion Cl- on the electrode surface, thus slowing down the corrosion. At this time, the corrosion rate of X80 steel decreases with the increase of so _ 4N _ 2-concentration, and when the mass fraction of so _ 4N _ (2) is more than 5%, the formation of electrode surface film will be destroyed by the high concentration of so _ 4 ~ (+) _ (2), and the corrosion rate will increase with the increase of so _ (4) ~ (2) concentration. The EIS of X80 steel in the acid red soil simulation solution containing 1 / 10SO4 / 2) showed high frequency capacitive and low frequency inductive reactance. According to the analysis of corrosion weight loss and corrosion polarization curve, the thickness and structure of corrosion product film have significant influence on the corrosion rate of X80 steel. When X80 steel was immersed in red soil simulated solution for 4 days, the surface of the electrode formed a relatively complete initial corrosion product film, the product film was protective, and the corrosion rate was the lowest. With the increase of soaking time, the surface of X80 steel is covered with intermediate corrosion product film, the product film is divided into two layers, the outer layer is loose and yellow, the inner layer is thin and black, and the protection of corrosion product film is very poor. The corrosion rate increased greatly. When the soaking time is 30 days, the surface of the sample is covered with the late corrosion product film, the thickness of the film increases, the product film is more loose and porous, and the corrosive ions in the solution can easily enter the metal substrate surface and react with it, so the corrosion rate is accelerated. At this time, the corrosion product film is less protective. The corrosion electrochemical data and corrosion morphology of X80 steel under simulated liquid film of red soil with different thickness and different pH value were analyzed. When the thickness of liquid film is 80 渭 m 路m ~ (-1) and pH = 4, the corrosion rate of X80 steel is affected by corrosion product film and oxygen diffusion. The minimum pH value of corrosion rate of X80 steel rises to 5 ~ 7, and the corrosion rate of X80 steel increases slightly in the process of oxygen reduction controlled corrosion. The corrosion rate of X80 steel decreases with the increase of pH value when the thickness of liquid film continues to increase, that is, when the thickness is 110 渭 m ~ 280 渭 m ~ (-1) 渭 m, which is consistent with the results obtained in bulk solution.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG178

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