设计加载阵列电极应力腐蚀实验装置, 针对我国典型的华南酸性红壤环境, 研究高强度低合金(HSLA) X80管线钢在破损防腐层(涂层)模拟缝隙下的应力腐蚀开裂(SCC)行为及影响因素, 采用电化学阻抗谱(EIS)监测加载电极的腐蚀电化学过程, 利用微电极监测防腐层剥离区局部电位和pH值变化, 探讨破损涂层下HSLA管线钢SCC行为和规律. 结果表明, 防腐层开放破损(漏点)处管线钢发生严重腐蚀: 不受力试样表面以阳极溶解占主导的均匀腐蚀为主, 而拉伸试样表面出现大量微裂纹和点蚀坑, 且沿试样划痕优先生长; 封闭的剥离区内部管线钢的腐蚀程度显著减缓. 同时, 对涂层破损点及剥离区深处管线钢的腐蚀现象和过程进行了讨论.

The three-layer polyethylene (3PE or 3LPE) coatings have been widely used on long-distance high pressure transmission pipelines in China. The 3PE coating tends to remain high insulating after disbonding from pipelines, and block the function of cathoidc protection (CP), similar to PE tape coatings that caused stress corrosion cracking (SCC) failure of pipeline. Disbondment 3PE coatings have been reported worldwide. Because of the high integrity and dielectric strength of 3PE coatings, SCC under disbonded 3PE coating becomes an important issue for integrity management and operation of high pressure pipelines. A great deal of researches have been conducting over the past 20 years to reproduce SCC of high strength low alloy (HSLA) pipeline in laboratory. Most of these studies were conducted in bulk solution condition. The methodology neglects particularity of the thin-layer electrolyte under disbonded coating which has been identified as one of the primary environmental factors related to SCC. In this context, a research project has been initiated on this subject. The overall goal is to systematically investigate corrosion scenarios and mechanochemical interaction of HSLA pipeline steels under disbonded 3PE coating in different soil environments, particularly to further mechanistic understanding the initiation of SCC on pipelines under disbonded coating. In this work, SCC behavior of API X80 pipeline steel under disbonded coating with defect was investigated in acidic soil solution by a crevice cell specially designed for simulating coating disbondment. The crevice cell was equipped with a multi-sample loading frame, through which multi specimens in the crevice cell can be loaded simultaneously. Electrochemical impedance spectroscopy (EIS) was applied to characterize local electrochemical process of the tensile specimens. Local environment parameters (potential and pH) were monitored by microelectrodes. Surface morphology of the corrosion specimens indicate that corrosion intensity of X80 steel decreased over the distance from the opening. Intensive anodic dissolution and microcrack initiation were preferential at the opening defect, whereas corrosion was markedly mitigated under disbonded coating. CO₂ content gradient is proposed for the special corrosion scenarios under coating disbondment.