A Proposal of AC Corrosion Mechanism of Carbon Steel in Cathodic Protection Condition

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• 作者：Andrea BrennaLuciano LazzariMarco Ormellese
• 会议时间：2013-09-01
• 关键词：cathodic protection ; AC interference ; corrosion ; steel pipeline
• 作者单位：olitecnico di Milano Via Mancinelli,7 Milan,20131 Italy
• 母体文献：2013中国国际管道会议暨第一届中国管道与储罐腐蚀与防护学术交流会论文集
• 会议名称：2013中国国际管道会议暨第一届中国管道与储罐腐蚀与防护学术交流会
• 会议地点：廊坊
• 主办单位：中国腐蚀与防护学会
• 语种：chi

摘要

Buried pipelines are provided with corrosion prevention systems, consisting of an insulating coating and a cathodic protection (CP) system which reduces (or halts) corrosion rate.If they run parallel to an AC source, as the high voltage transmission line (HVTL), AC interference can take place causing corrosion corresponding to coating defects, even if the-0.850 V CSE criterion is matched.Electrochemical tests were carried out on carbon steel in soil simulating environment: overprotection (potential lower than-1.1 V CSE) seems to be the most dangerous condition in the presence of AC interference.In this paper, a two-step corrosion mechanism is proposed: 1) AC causes the electro-mechanical breakdown of the passive film formed on steel in CP condition; 2) corrosion occurs if the pH at the metalto-electrolyte interface is close to 14.Tests on passive metals show that AC has a harmful effect on passive condition, reducing the critical chlorides threshold and causing the film breakdown over a critical alternating electric field (in the order of 106 V/cm) within the passive film.After film breakdown, corrosion occurs ifpH is about 14, achievable in overprotection condition and in the presence of AC.