A New Understanding of Stress Corrosion Cracking Mechanism of X80 Pipeline Steel at Passive Potential in High-pH Solutions  

作　　者：Lin Fan Zhi-Yong Liu Wei-Min Guo Jian Hou Cui-Wei Du Xiao-Gang Li 

机构地区：[1]Corrosion and Protection Center,University of Science and Technology Beijing [2]State Key Laboratory for Marine Corrosion and Protection,Luoyang Ship Material Research Institute

出　　处：《Acta Metallurgica Sinica(English Letters)》2015年第7期866-875,共10页金属学报（英文版）

基　　金：supported by the National Natural Science Foundation of China (Nos.51471034,51131001 and 51171025)

摘　　要：Susceptibilities to stress corrosion cracking（SCC） of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or p H value at a passive potential of-200 m V vs SCE were investigated by slow strain rate tensile test.In order to explore the SCC mechanism and the evaluation criterion for the SCC susceptibility of the steel in passive state,electrochemical measurements were taken.Potentiodynamic polarization curves were obtained at different potential sweep rates,and electrochemical impedance spectroscopy measurements were taken after fast polarization to the passive potential.The effects of chloride ion and p H on SCC behaviors of X80 steel at the passive potential were also discussed.The results showed that the SCC mechanism of X80 pipeline steel was greatly influenced by the passive film formed in these solutions.The SCC behaviors followed the film suppressed anodic dissolution mechanism in these circumstances,because the filming process accounted for a considerable proportion of the overall electrode process.The criteria for evaluating the SCC susceptibility of the steel at passive potential were proposed and validated.Decreasing in the concentration of chloride ion or increasing in p H value resulted in the reduction in SCC susceptibility.The existence of chloride ion greatly lowered the passivation tendency and the film stability,while its concentration determined the dissolution rate of the steel matrix.Higher p H value was responsible for the stable and tenacious passive films and the high repassivation capability.It was also inclined to lower the anodic dissolution rate at crack tips by retarding the cathodic oxygen reduction.Susceptibilities to stress corrosion cracking（SCC） of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or p H value at a passive potential of-200 m V vs SCE were investigated by slow strain rate tensile test.In order to explore the SCC mechanism and the evaluation criterion for the SCC susceptibility of the steel in passive state,electrochemical measurements were taken.Potentiodynamic polarization curves were obtained at different potential sweep rates,and electrochemical impedance spectroscopy measurements were taken after fast polarization to the passive potential.The effects of chloride ion and p H on SCC behaviors of X80 steel at the passive potential were also discussed.The results showed that the SCC mechanism of X80 pipeline steel was greatly influenced by the passive film formed in these solutions.The SCC behaviors followed the film suppressed anodic dissolution mechanism in these circumstances,because the filming process accounted for a considerable proportion of the overall electrode process.The criteria for evaluating the SCC susceptibility of the steel at passive potential were proposed and validated.Decreasing in the concentration of chloride ion or increasing in p H value resulted in the reduction in SCC susceptibility.The existence of chloride ion greatly lowered the passivation tendency and the film stability,while its concentration determined the dissolution rate of the steel matrix.Higher p H value was responsible for the stable and tenacious passive films and the high repassivation capability.It was also inclined to lower the anodic dissolution rate at crack tips by retarding the cathodic oxygen reduction.

关 键 词：Pipeline steel Stress corrosion cracking （SCC） PASSIVATION Chloride ion pH value 

分 类 号：TG142.15[一般工业技术—材料科学与工程]