交流电、阴极极化和微生物多因素作用下剥离涂层内X80管线钢应力腐蚀机理研究

It is one of the most important threats for safe working of the buried pipeline steel that stress corrosion cracking (SCC) occurs in a crevice under a disbonded coating due to shielding effect of the coating. Field observation and laboratory studying show that the CP, alternating currents (AC) and microbes have an obvious effect on stress corrosion of the steel under the disbonded coating. However, effects of the CP, AC and the microbes on corrosion of the steel are seldom investigated under the disbonded coatings. In this project, experimental devices will be built in order to simulate the disbonded coatings, the stress and the AC. By using electricity, electrochemistry, micro-electrodes, microbial technology, chemical analysis, surface analysis, and so on, a disbonding process of the coating, variations of micro-environments, metabolism of the microbes, adsorption and structural changing of biofilms are investigated in the crevice under the disbonded coating. The penetration and diffusion of hydrogen atoms, pitting corrosion, initiation and propagation of the SCC cracks, chemical and electrochemical variations of the micro-environments in tips of the cracks are also studied. The finish of the project will provide theoretical basis for performance optimization, corrosion and protection of the pipelines, and safety-evaluation methods of the initiation and propagation of the SCC of X80 pipeline steel.

由于剥离涂层对阴极保护的屏蔽效应，因此地下管线剥离涂层内管线钢应力腐蚀开裂是管线安全运行的重要威胁。现场腐蚀调查及实验室研究结果表明，交流电、阴极极化和微生物参与并显著影响剥离涂层内管线钢应力腐蚀行为。然而上述多因素作用下剥离涂层内管线钢应力腐蚀研究却未见报道。本项目拟构建剥离涂层模拟试验装置，采用电学，电化学、微电极、微生物、化学分析和表面分析等测试技术，在上述多因素作用下，研究X80管线钢表面涂层的剥离规律，以及剥离涂层内微区环境、微生物代谢过程、微生物膜附着状态和结构变化规律；研究剥离涂层内X80管线钢表面氢渗透和扩散的影响机理，X80管线钢点蚀及应力腐蚀裂纹萌生和扩展不同演化阶段的影响机理，以及裂纹尖端局部微环境化学/电化学过程的变化规律，建立上述多因素作用下剥离涂层内X80管线钢应力腐蚀裂纹萌生和扩展安全评价方法，为我国高强度管线钢的性能优化、防护及安全评价提供科学依据。

高强管线钢的土壤腐蚀环境复杂，其中交流电流（AC）、硫酸盐还原菌（SRB）和应力是影响埋地管道腐蚀失效的重要因素，各因素之间可能存在协同作用加速高强管线钢腐蚀。此外，土壤环境中管线失效常发生在剥离涂层下，剥离涂层下的腐蚀规律与裸钢的腐蚀规律存在较大差异。目前，对于多因素共存时剥离涂层下管线钢腐蚀规律和机理的研究少有报道。本项目设计了模拟剥离涂层情况下的阵列电极实验原位监测实验装置，揭示了酸性红壤中剥离涂层下X80钢的腐蚀机制。SRB利用X80钢作为电子供体，还可以以土壤环境中的高价Fe氧化物作等为末端电子受体，实现胞外电子转移，加速管线钢腐蚀。研究了酸性红壤环境中剥离涂层下弹性应力和SRB耦合作用对X80钢腐蚀的影响规律，SRB和外加弹性应力共同作用提高了剥离涂层下管线钢电化学活性，促进管线钢腐蚀。弹性应力改变了剥离涂层下管线钢的局部点蚀形貌，管线钢局部腐蚀开裂敏感性提高。进一步研究了交流电、SRB和外加弹性应力多因素耦合下剥离涂层下管线钢的腐蚀行为。发现，多因素协同作用增加管线钢腐蚀驱动力，管线钢的生物电化学腐蚀活性升高，阴阳极反应过程驱动力增加。剥离涂层下管线钢的腐蚀机制为阳极溶解机制和氢脆混合机制。研究结果将为酸性红壤环境中剥离涂层下高强管线腐蚀及应力腐蚀机制，安全评价方法和预防提供科学依据。