应用电化学极化技术、电化学阻抗谱、模拟浸泡实验, 研究了X70钢在模拟潮湿存储环境中点蚀的发生机制及规律. 结果表明, X70钢在模拟潮湿存储环境中可以发生点蚀, 导致点蚀发生的腐蚀介质来自于层流冷却水中的腐蚀性物质,其中HCO3-和NO3-是致钝剂, 而Cl-和SO42-可破坏钝化膜, 促进点蚀发生. 在0.5 mol/L的NaHCO3介质中当Cl-浓度达到0.02 mol/L时钝化膜即失去保护性. Cl-浓度是影响点蚀的萌生和发展的关键因素, 当其浓度较低时点蚀容易形核, 但仅有少数能够长大; 而当其浓度适中(约0.149 mol/L)时点蚀敏感性最高, 点蚀容易长大; 当其浓度过高时发生均匀腐蚀,点蚀难以长大.
Pitting mechanism and behaviour of X70 pipeline steel in humid storage environments were investigated using electrochemical polarization curves, electrochemical impedance spectrums (EIS), immersing corrosion tests and corrosion morphology observation through SEM. It was demonstrated that pitting of X70 pipeline steel occurred in simulated moist storage environments, for which the corrosive substances came from the residual species in laminar cooling water introduced during steel manufacture processes. HCO3 - and NO3− are passivating agents, Cl− and SO42− would destroyed the passivation layer, which could lead to pitting. In solution with 0.5 mol/L NaHCO3, 0.02 mol/L Cl− was enough to break the passivation layer. Cl− concentration is a key factor for pitting initiation and propagation. When the Cl− concentration was relatively low, pitting could initiate but was hard to grow up. When the Cl− concentration was moderate (about 0.149 mol/L), pitting sensitivity was the highest because pitting was easy to grow up. However, if the concentration of Cl− was too high, uniform corrosion occurred.
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