酸性油气环境中H2S-Cl-协同作用促进不锈钢钝化膜破裂及点蚀行为研究

The problem of Cl- induced passive film breakdown and pitting corrosion has been paid extensive concern by corrosion scientists. It is common in sour oil-gas environment that coexistence of H2S and Cl- will act synergistically to promote passive film breakdown and accelerate pitting. It is necessary to illustrate the synergistic effect of H2S-Cl- on passive film breakdown and pitting behavior in order to guarantee the safe operation of oil-gas industry. In this proposed program, the composition and property of passive film will be characterized after corrosion in H2S-Cl- containing environment, the charge carrier density and transfer process in the passive film will be characterized using electrochemical methods. The distribution of S and Cl in the passive film will be analysed by associating with charge carrier density and transfer process, in order to illustrate the effect of H2S-Cl- on the chemical process of passive film corrosion and the physical mechanism of passive film breakdown. By employing artificial pit electrode, the nucleation and growth of metastable pitting was monitored using electrochemical methods. The pit geometry, cover over the pit mouth and precipitation of salt films during pit growth will be analysed using materials characterization methods, in order to illustrate the influential mechanism of H2S-Cl- on transformation of metastable pitting to stable pitting. On studying the stable pitting behavior, the corrosion process and mechanism of stainless steel substrate in H2S-Cl- containing environment will be illustrated. The pit morphology, depth, corrosion product and so on will be monitored during pitting growth. 3D graphs will be employed to characterize the pit growth morphology and construct pitting model, in order to provide theoretical support for corrosion protection and safety monitoring in sour oil-gas fields.

Cl-引起钝化膜破裂及点蚀是腐蚀界广泛关注的问题，在酸性油气环境中普遍存在的H2S与Cl-能够协同作用促进钝化膜破裂并加速点蚀，明确其协同作用机制及点蚀行为规律是保证油气工业安全运行的必要条件。本项目拟通过表征钝化膜在H2S-Cl-环境中腐蚀后的成分与性能，利用电化学方法表征钝化膜中的载流子密度与电荷传输过程，分析S、Cl在膜中的分布与电荷传输、载流子密度的关系，明确H2S-Cl-促进钝化膜腐蚀的化学过程及破裂的物理机制。使用人工点蚀电极，利用电化学方法监测亚稳态点蚀的萌生与生长，利用材料表征方法分析蚀坑形状、覆盖物和沉积盐膜的演化规律，明确H2S-Cl-对亚稳态点蚀向稳态转变的作用机制。研究稳态点蚀行为，明确基体成分在H2S-Cl-环境中的腐蚀过程及作用机理，分析点蚀形貌、深度、腐蚀产物等演化规律，用3D图表征点蚀生长形貌并构建点蚀模型，为酸性油气环境的腐蚀防护与安全预测提供理论指导。

Cl-引起钝化膜破裂及点蚀是腐蚀界广泛关注的问题，在酸性油气环境中普遍存在的Cl-与S2-能够协同作用促进钝化膜破裂并加速点蚀，明确其协同作用机制及点蚀行为规律是保证油气工业安全运行的必要条件。本项目选用304与17-4PH不锈钢，利用极化曲线与交流阻抗测试研究其在Cl--S2-溶液中的电化学腐蚀行为，用XPS、椭圆偏光表征304不锈钢在Cl--S2-环境中腐蚀后的钝化膜成分与厚度，分析S2-对腐蚀行为及钝化膜破裂的作用机理。对不同热处理态的17-4PH不锈钢，表征其显微组织与硬度，研究其在Cl--S2-环境中的电化学腐蚀行为。主要结论如下：.（1）Cl--S2-环境中的S2-浓度升高使阴极电流密度减小，阳极电流与维钝电流密度增大，OCP、Ezcp和点蚀电位降低，点蚀电位降低与S2-浓度升高之间存在对数关系。.（2）随Cl--S2-环境中的S2-浓度增大，钝化膜电阻与电荷转移电阻呈降低趋势，钝化膜保护性变差，电荷传递速率增大，腐蚀过程加快。.（3）随Cl--S2-环境中的S2-浓度增大，钝化膜中元素Cr、Fe组分减少，元素S组分增多，元素Ni变化不明显。其中，Cr2O3呈减少趋势，CrCl3、Cr2S3、Fe2O3和FeS呈增多趋势。.（4）304在含Cl-溶液中腐蚀后钝化膜最薄，在Cl--S2-共存的溶液环境中腐蚀后，钝化膜厚度介于3.248~8.304 nm。.（5）17-4PH在1050℃固溶后含析出物很少，仍含有铁素体，比热轧态中铁素体数量减少；在固溶+时效后，有Cu沉淀相析出；时效温度升高，沉淀相增多并长大聚集。17-4PH在固溶淬火后硬度最低，在460℃时效后硬度最高，时效温度升高，硬度呈降低趋势。不同热处理态17-4PH不锈钢在Cl--S2-环境中的特征电位与维钝电流密度变化较小。. 实验结果对不锈钢设计、腐蚀防护与安全预测具有指导意义。