N80油管钢在含CO₂/H₂S高温高压两相介质中的电化学腐蚀行为及缓蚀机理研究

【作者】 任呈强；

【导师】 刘道新；

【作者基本信息】 西北工业大学 ， 材料学， 2003， 硕士

【摘要】 成功地制备了用于高温高压电化学腐蚀研究用Ag／AgCl参比电极，在模拟气田腐蚀工况环境下，采用交流阻抗和动电位扫描等电化学技术，辅以SEM、XRD等表面分析方法，研究了N80油管钢在高温高压下含CO₂和（或）H₂S的两相介质中的腐蚀行为和吸附型缓蚀剂的缓蚀机理，特别探讨了腐蚀产物膜对腐蚀过程的影响，分析了腐蚀产物膜的力学性能与油管钢腐蚀速率之间的关系。 研究结果表明：在CO₂环境中，N80油管钢的电化学腐蚀阳极过程受电化学活化控制，OH^-在表面的吸附放电产生吸附中间体FeOH_ads和FeOH⁺_ads，最终生成Fe²⁺；阴极过程由H₂CO₃和HCO₃^-还原为主。随着腐蚀产物膜的形成，交流阻抗谱会发生变化，表现为高频扩展和低频收缩，反应阻力增大。腐蚀产物膜完整覆盖后表现为受电化学活化控制的均匀腐蚀特征。 在H₂S／CO₂环境中，HS^-吸附能力强，阳极吸附中间体吸附量明显增加，裸金属时阳极反应受到较大程度的促进。阴极以H₂S的还原为主。硫化物腐蚀产物膜容易破裂，由此导致局部腐蚀产生。由于硫化物腐蚀产物膜对腐蚀介质起到很强的扩散阻滞作用，出现Warburg阻抗，使腐蚀过程受扩散控制。 CO₂分压对腐蚀的影响主要表现在裸金属表面，增大分压使N80钢表面活性增大，腐蚀加速。形成完整的膜后，分压影响很小。加入H₂S后，H₂S含量较小时以CO₂腐蚀为主，腐蚀得到较大程度的促进；H₂S含量增大，转化为以H₂S腐蚀为主，出现局部腐蚀；继续增大H₂S含量，局部腐蚀反而受到抑制。 噻唑衍生物的加入改变了腐蚀产物膜的内层结构，抑制局部腐蚀的发生。噻唑的缓蚀机理是几何覆盖效应，因吸附覆盖度不大导致缓蚀效率不高。同时噻唑难以在腐蚀产物膜上吸附，腐蚀产物膜形成后对腐蚀速率的影响明显减弱。咪唑啉衍生物属于阳极型缓蚀剂，缓蚀机理为“负催化效应”，不仅能在金属表面上吸附，而且能与腐蚀产物膜协调作用，起到较好的缓蚀效果。 SEM分析显示，CO₂腐蚀产物膜致密而均匀，表现为均匀腐蚀，H₂S腐蚀产物膜晶粒粗大，并有破裂，引起局部腐蚀坑出现。这与本文提出的电化学模型相吻合。 确定了腐蚀产物膜的力学性能与N80钢的腐蚀速率之间的关系。N80钢的腐蚀速率随腐蚀产物膜的硬度升高而降低，随产物膜结合强度下降而增大。更多还原

【Abstract】 An Ag/AgCl (saturated KC1) electrode, which was used as an internal reference electrode in the electrochemical research under the conditions of high temperature and high pressure, was developed by means of electrolyzing. In the simulating gas field downhole CO2 and H2S/CO2 corrosion environment under high temperature and high pressure conditions, the mechanisms of corrosion and inhibition on the N80 steel were studied and the effect on the corrosion behavior of corrosion scale was investigated by using AC impedance spectroscopy, potentiodynamic polarization technique, SEM and XRD et. The relation of the mechanical properties of the corrosion scale and corrosion rate of N80 steel was analyzed also. The results show that:In the CO2 corrosion environment, the anodic reactions are controlled by chemical activation step. OH" adsorbs on the surface of N80 steel, and then become into FeOHads and FeOH+ads, Fe2+ is found at last. The reduction of H2CO3 and HCO3-is the most important cathodic reaction. The EIS (Electrochemical Impedance Spectroscopy) curves change with the scale covering the electrode surface. The capacitive arc in high frequency section extends but that contract in low frequency section. The general corrosion occurs.In the H2S/CO2 corrosion environment, the amount of adsorptions increases because of the high adsorption capacity of HS-. The reduction of H2S is the main cathodic reaction. The anodic and cathodic reactions are accelerated to different degree. The mass transport process through sulfide film is checked. It was found that the corrosion behavior of the steel is controlled by mass diffusion. The splits of sulfide film induce the pitting.The partial pressure of CO2 mainly affects the corrosion behavior of the bare steel. The electrochemical activity of N80 steel increases with the partial pressure of CO2 increasing, so the corrosion rate is accelerated. The partial pressure of CO2 has little effect on the N80 steel as covered by integrated corrosion scale. CO2 corrosion is predominant when the environment contains little H2S, but the corrosion rate is accelerated. H2S corrosion becomes the main one with the partial pressure of H2S increasing. Pitting occurs. However, when the partial pressure of H2S increases to 2psi, the tendency of pitting reduces.The derivation of thiazo changes the structure of inner corrosion scale and restrains pitting. The inhibition mechanism is "geometric blocking effect". The inhibition efficiency is very low due to the low adsorption capacity of the inhibitor. Itcannot adsorb on the corrosion scale, so the inhibition efficiency obviously reduces after the corrosion scale covering the surface of N80 steel. Imidazoline, as an anodic inhibitor, decreases the corrosion rate by negative catalytic effect. It can not only adsorb on the surface of N80 steel, but also cooperate with corrosion scale, so it has good inhibitive effect.It can be found from SEM analysis that: CO2 corrosion scale is compact and uniformity, so N80 steel exhibits general corrosion; H2S corrosion scale is made up of big crystals and has pitting caused by scale split. These results coincide with the electrochemical model put forward in the paper.The investigation results on the relations of the mechanical properties of the corrosion scale and corrosion rate show that: The corrosion rate increases with the bounding strengthen of the scale to N80 steel and hardness of scale decreasing.更多还原