管线钢腐蚀的材料因素与环境因素关联性研究

【作者】 曹然伟；

【导师】 任呈强；

【作者基本信息】 西南石油大学 ， 材料学， 2011， 硕士

【摘要】 基于某气田单井集输管线腐蚀穿孔现象,调研了集输工况,在此基础上开展了不同管材的腐蚀行为研究,得到了各自的腐蚀速率变化规律,并采用电化学方法分析它们的腐蚀机理,结合正交实验方法、金相分析、物相分析和形貌分析等手段,探讨了管线钢腐蚀的材料因素与环境因素的关联性,为以后该气田在单井集输管线的材料选择和防腐措施工作提供思路。在模拟该气田集输系统的腐蚀介质中,对20G、15CrMo、20#三种钢进行了典型环境因素的正交实验和单因素实验。结果表明：影响20G、15CrMo、20#钢的环境因素排序存在差异,影响管线钢C02腐蚀最显著的四个因素分别是温度、pH值、HC03-和Cl-。HC03-和C02含量较高时,有利于促进钝化,15CrMo钢比20G钢耐蚀,而变化其它因素时,20G钢比15CrMo钢耐蚀,20#钢的腐蚀速率最高。并结合实际环境讨论了环境因素的作用机制。交流阻抗和极化曲线测试结果表明,20G、15CrMo、20#三种钢在该实验环境中的腐蚀电化学机理是一致的,其腐蚀速率主要受阴极过程控制,腐蚀产物对腐蚀速率也有着重要影响。XRD分析表明三种钢的腐蚀产物的物相均为FeC03,但SEM分析发现腐蚀产物的形貌存在差异。20G钢的腐蚀产物微观取向性很强,对基体的保护性较好；15CrMo钢腐蚀产物覆盖致密,但是裂痕的存在一定程度上削弱了产物本身的保护性；而20#钢腐蚀产物形貌缺陷较多,故对腐蚀介质的阻挡作用最小。研究发现,三种钢的显微组织和成分对其腐蚀速率也有直接的影响。因此,材料因素和环境因素共同决定了管线钢的腐蚀行为。故实验条件下在C02和HC03-含量较高时可选用15CrMo钢,其它环境中选用20G钢,为了更好地控制腐蚀,建议添加缓蚀剂防腐。更多还原

【Abstract】 Based on the failure analysis of the single well gathering pipeline, corrosion tests were carried out to simulate single gathering pipeline environment in order to obtain corrosion rates of different types of pipeline steels. The polarization curves and impedance spectroscopy were also adapted to analyze corrosion mechanisms of different materials by means of electrochemical methods. Orthogonal test, matellographic analysis, components analysis, feature analysis were used to discuss the relevance between material factors and environmental factors during the course of corrosion. It is hoped to offer the reference for the material selection of single gathering pipeline in oil and gas fields.Orthogonal and single factor experiments were carried out on 20G,15CrMo,20# in a simulated gathering pipeline environment. Differences was founded in ranking of the different environmental factors. Temperature,pH,HCO3- and Cl- play most important role on the corrosion. With the increasing of the concentration of HCO3-and CO2, the corrosion resistance of 15CrMo was better than that of 20G, for it was easy to be passive, while 20G was better than 15CrMo when other factors were changed. The corrosion rate of 20# was the highest one among the steels. Field environment conditions were combined to discuss the role of environmental factors.The polarization curves and impedance spectroscopy shows the electrochemical reaction mechanism of the 20G,15CrMo,20# were same in the experiment environment, and the corrosion rate of was mainly controlled by the cathodic process. It also found the corrosion products play an important influence on the corrosion rate.XRD shows the corrosion products on the three steels were FeCO3, but the morphology of corrosion products was different by SEM. The corrosion products of 20G were orderly relative,so the corrosion products of 20G could provide the best protection to the matrix. Although the corrosion products of 15CrMo were closed, but there were cracks in the morphology, so the protection to the matrix was poorer than 20G. There are many defects in the morphology of corrosion film on 20#. It can be infer that it could not block off the corrosion medium, so the protection is the worst one.Comprehensive studies showed the microstructure and alloy element of materials had a direct effect on the corrosion resistance of the materials. Data showed that the corrosion rate of pipeline steel was both determined by environmental factors and material factors.15CrMo was suggested to be used in the condition containing the higher concentration of CO2 and HCO3-, otherwise 20G was proposed. Corrosion inhibitors should be added in order to reduce the corrosion rate furtherly.更多还原