Brenna Andrea, Beretta Silvia, Ormellese Marco
Dipartimento di Chimica, Materiali e Ingegneria Chimica "Giulio Natta", Politecnico di Milano, Milan, Italy.
Materials (Basel). 2020 May 7;13(9):2158. doi: 10.3390/ma13092158.
Cathodic protection (CP), in combination with an insulating coating, is a preventative system to control corrosion of buried carbon steel pipes. The corrosion protection of coating defects is achieved by means of a cathodic polarization below the protection potential, namely -0.85 V vs. CSE (CSE, copper-copper sulfate reference electrode) for carbon steel in aerated soil. The presence of alternating current (AC) interference, induced by high-voltage power lines (HVPL) or AC-electrified railways, may represent a corrosion threat for coated carbon steel structures, although the potential protection criterion is matched. Nowadays, the protection criteria in the presence of AC, as well as AC corrosion mechanisms in CP condition, are still controversial and discussed. This paper deals with a narrative literature review, which includes selected journal articles, conference proceedings and grey literature, on the assessment, acceptable criteria and corrosion mechanism of carbon steel structures in CP condition with AC interference. The study shows that the assessment of AC corrosion likelihood should be based on the measurement of AC and DC (direct current) related parameters, namely AC voltage, AC and DC densities and potential measurements. Threshold values of the mentioned parameters are discussed. Overprotection ( < -1.2 V vs. CSE) is the most dangerous condition in the presence of AC: the combination of strong alkalization close to the coating defect due to the high CP current density and the action of AC interference provokes localized corrosion of carbon steel.
阴极保护（CP）与绝缘涂层相结合，是一种用于控制埋地碳钢管道腐蚀的预防系统。通过在保护电位以下进行阴极极化来实现对涂层缺陷的腐蚀防护，对于充气土壤中的碳钢，该保护电位相对于铜 - 硫酸铜参比电极（CSE）为 -0.85 V。尽管满足了潜在的保护标准，但由高压电力线（HVPL）或交流电气化铁路引起的交流电流（AC）干扰的存在，可能对涂层碳钢结构构成腐蚀威胁。如今，存在交流电流时的保护标准以及阴极保护条件下的交流腐蚀机制仍存在争议并有待讨论。本文对关于存在交流干扰的阴极保护条件下碳钢结构的评估、可接受标准和腐蚀机制的文献进行了叙述性综述，其中包括精选的期刊文章、会议论文集和灰色文献。研究表明，交流腐蚀可能性的评估应基于与交流和直流（DC）相关参数的测量，即交流电压、交流和直流电流密度以及电位测量。文中讨论了上述参数的阈值。过保护（相对于CSE < -1.2 V）是存在交流电流时最危险的情况：由于高阴极保护电流密度导致靠近涂层缺陷处强烈碱化，再加上交流干扰的作用，会引发碳钢的局部腐蚀。
