杂散电流干扰和阴极保护作用下碳钢腐蚀规律研究

Corrosion Behavior of Carbon Steel in Interference of Stray Current and Cathodic Protection

目的探讨杂散电流和阴极保护二者共同作用对碳钢腐蚀的影响。方法在碳钢管表面手工涂刷涂层并制造小块破损点,研究Q235碳钢在涂层破损后,受单纯直流杂散电流干扰、单纯阴极保护以及二者共同作用时随时间变化的电化学交流阻抗图谱(EIS),通过图谱信息以及图谱数据拟合进行分析。结果所有条件下,Bode图低频阻抗和Nyquist图容抗弧半径都随时间延长而逐渐增加。通过图谱和数据拟合发现,单纯杂散电流条件下,杂散电流越大,电化学阻抗越小,浸泡15天时,20 m A杂散电流条件下的极化电阻达到200 m A条件下的4倍。阴极保护对杂散电流腐蚀具有防护作用,无论是单独施加阴保,还是杂散+阴保共同作用,-1000 m V(vs.CSE)与-850 m V(vs.CSE)横向对比,总是-1000 m V条件下的极化电阻更高。一定程度上,阴保电位越负,极化电阻越大,保护效果越好。结论在一定范围内,不论是单独施加,还是共同作用,总是杂散电流越小,阴极保护电位越负,对碳钢的保护效果越好,腐蚀程度越轻。利用电化学交流阻抗技术监测管道腐蚀状况是可行的。

Objective To investigate the corrosion behavior change of carbon steel with immersion time in the interference of stray current and cathodic protection （CP）. Methods In this paper, man-made small damage points were made on carbon steel pipe which was coated. The electrochemical impedance spectra （EIS） of the Q235 carbon steel with the damaged coating were studied, which were affected by the DC stray current interference, the cathodic protection and the combined action of DC stray and CP over time. The analysis was conducted according to spectral information and spectral data fitting. Results All the low-frequency impedance in Bode diagrams and capacitive reactance arc radius of Nyquist diagrams of EIS spectra under any conditions were gradually increasing over time. Through the spectra and data fitting, it was found that the larger the stray current was, the more serious the corrosion was; when the immersing time reached 15 days, the polarization resistance under the condition of stray current of 20 mA was four times as much as that under the condition of stray current of 200 mA. Cathodic protection had a protective effect on the stray current corrosion. Comparing the conditions of -1000 mV （CSE） and -850 mV （CSE） , the polarization resistances un- der the condition of -1000 mV were higher all the time. Within a certain limits, the more negative the cathodic potential was, the greater the polarization resistance was, and the better protection effect was obtained. Conclusion Within a certain limits, no matter stray current or cathodic protection is applied alone or together, it is always found that with smaller stray current and more negative cathodic protection potential, the protective effect for carbon steel is better and the corrosion degree is less. It is feasible to monitor the corrosion of pipeline by EIS technique.