有涂层缺陷的X70管线钢在模拟包头土壤溶液中的腐蚀行为

Corrosion Behaviour of X70 Pipeline Steel Under Coating Holiday in Simulated Solution of Baotou Soil

测定了内蒙古包头地区土壤的基本理化性质,制作了占试样总面积分别为0.39%、1.57%和6.28%的破损涂层缺陷试验,测定了涂层缺陷试样在不同浸泡时间内在包头模拟溶液中的交流阻抗谱,并连续测定了试样的自腐蚀电位Ecorr。试验结果表明:交流阻抗谱的Nyquist曲线显示为典型的具有扩散控制的双容抗弧,并且随浸泡时间的延长,曲线的容抗弧先增加而后缩小,说明在破损涂层缺陷状态下,试样的腐蚀程度随着浸泡时间先减小后加剧。分析后认为,模拟溶液向涂层内部的渗透以及涂层缺陷附近的涂层与钢基体间的缝隙腐蚀是导致涂层缺陷下X70管线钢腐蚀的主要原因。

Basic physical and chemical properties of Baotou soil were evaluated. The samples of breaking coating holiday were made by controlling the ratio of the breaking coating holiday to the tota area of the sample at 0. 39%, 1. 57% and 6.28% , respectively. X70 pipeline steel samples under different coating holiday were soaked in simulated solution of Baotou soil. The natural corrosion potential of the specimens was determined, and the E1S of samples in different time (2,14 days and 30 days) were measured. The experiments showed that the Nyquist curve of AC impedance spectroscopy had typical twinned arc of diffusion controlled, and the arc of capacitor and resistor was increased firstly and reduced later with increasing the soaking time. These explain that the corrosion of samples under breaking coating holiday increases firstly and reduces later as increasing time. It was proposed that penetration of soils simulation solution into coating and the crevice corrosion between coating holidays and surface of steel matrix were main reasons to corrosion on X70 pipeline steels with coating holidays.