L245管线钢及焊缝在硫酸盐还原菌环境下的腐蚀行为研究

目的 通过实验模拟硫酸盐还原菌对L245钢及焊缝的腐蚀行为,探究硫酸盐还原菌对母材和焊缝的腐蚀过程及差异.方法 采用静态浸泡法研究了L245管线钢及焊缝在硫酸盐还原菌(SRB)条件下的3个不同浸泡时段的腐蚀行为.通过扫描电镜(SEM)、能谱仪(EDS)、聚焦离子束显微镜(FIB-SEM)和激光共聚焦显微镜(CLSM)等测试设备,对试样母材及焊缝区的膜生长过程和腐蚀特征差异进行了表征分析.结果 焊缝区和母材区的腐蚀特征均表现为微生物膜下的局部腐蚀,且点蚀程度随着浸泡时间延长而加重.在腐蚀初期(24 h),焊缝区胞外聚合物(EPS)生长速度要高于母材区,浸泡72 h后,微生物膜已完全覆盖试样表面.腐蚀末期(168 h)膜结构的研究结果表明,大量SRB个体存在于膜中,这是造成点蚀的关键原因.试样去除微生物膜后,经测量发现,焊缝区平均点蚀深度和最大点蚀坑深度均高于母材区,熔合线附近区域的点蚀尤为严重.结论 微生物膜生长对碳钢L245的腐蚀萌生及加速起到了关键作用,焊缝区对SRB引发的点蚀敏感性更高.初步揭示了细菌生长趋势、膜生长过程、点蚀发展这三者之间的对应关系.

Study on Corrosion Behavior of L245 Pipeline Steel and Joints in Sulfate Reducing Bacteria Environment

The corrosion process and difference between base metal and weld were explored by simulating immersion corrosion test of L245 pipeline steel with welding seam under the action of sulfate-reducing bacteria. Immersion corrosion test in SRB environment were performed at different periods. SEM&EDS, FIB-SEM, CLSM and other analysis methods were used to study the corrosion behavior of weld zone and base metal zone in SRB environment. The results showed that Localized corrosion happened under the biofilm, submembrane pitting were becoming more aggravated with the immersion time extending. The biofilm on weld zone generated faster than that generated on base metal zone in the early stage 24 h, the surface was completely covered by biofilm until 72 h immersion. At the end stage 168 h, biofilm structure showed that a mass of SRB existed in the biofilm, which was the main factor of the pitting corrosion. By measuring the pitting, it was found that the average and the maximum pitting depth on weld zone were higher than that on the base metal zone, and pitting corrosion was more severe in the area near the fusion line. The growth of biofilm accelerated the corrosion of carbon steel L245. The weld zone was more sensitive to SRB-induced corrosion. This study revealed the corresponding relationships among bacterial growth trend, biofilm growth process and pitting development. The composition, metallographic structure deference between weld and base metal zone and electrical activity of SRB were the main factors that caused more serious pitting corrosion on weld zone compared to the base metal zone.