拉应力作用下X80管线钢预制长槽缺陷周围局部腐蚀行为

Local Corrosion Behavior around Artificial Groove Defect of X80 Pipeline Steel under the Tensile Stress

目的评价在应力作用下,土壤中管道长槽缺陷周围的腐蚀速率。方法采用有限元方法分析了100%屈服应力下,X80管线钢垂直于应力方向的长槽形人造缺陷周围的应力分布。采用扫描电化学显微镜技术(SECM)测试了100%屈服应力下,库尔勒土壤模拟溶液中预浸40天的X80管线钢试件人造缺陷附近的腐蚀电化学活性,通过电流场模型和法拉第定律计算并估计了人造缺陷端部应力集中区和缺陷两侧在库尔勒土壤中的腐蚀速率。结果外加应力下,长槽形预制缺陷端部产生应力集中,缺陷两端局部应力达到试件所施加应力的2～3.4倍。在土壤模拟溶液中,缺陷端部应力集中区为阳极区,缺陷两侧低应力区为阴极区。预制缺陷端部应力集中区域作为阳极,有腐蚀加速的趋势,存在点蚀倾向。结论在拉应力作用下,库尔勒土壤模拟溶液中X80钢缺陷端部平均腐蚀速率可达0.12 mm/a,点蚀速率可达0.9～1.7 mm/a,分别为自然腐蚀速率的1.25倍和9.4～17.7倍,即在应力集中位置更易发生点蚀。

The work aims to evaluate the corrosion rate around the artificial groove defect of pipeline in soil under the tensile stress.The stress distribution around the long groove artificial defect of the X80 pipeline perpendicular to stress direction under 100%yield stress was analyzed by finite element.The electrochemical activity around the artificial defect of X80 pipeline steel samples after immersed in the pre-prepared Korla soil simulated solution for 40 days was measured with the Scanning Electrochemical Microscopy(SECM).The corrosion rate of the stress concentration area at the artificial defect ends and both sides of defects was calculated and estimated by the model of current field and the Faraday's law.The ends of long grooved prefabricated defects had stress concentration under external stress and local stress on both ends of defects reached 2~3.4 times of external stress on samples.In the soil simulation solution,the stress concentration area at ends of defects was anodic area,while the low stress area at both sides of defects was cathodic area.The stress concentration area at the end of prefabricated defects as anodic area could accelerate the corrosion and tended to appear pitting.Under tensile stress,the average corrosion and pitting rates of defect ends of X80 steel in Korla soil simulation solution are 0.12 mm/a and 0.9~1.7 mm/a respectively,being 1.25 and 9.4~17.7 times of natural corrosion rate.Therefore,the stress concentration area is easy to generate pitting.