Effect of Temperature on CO2-induced Corrosion Behavior of 5Cr Steel in a Simulated Oilfield Produced High-temperature and High-pressured Water
The CO2-induced corrosion of 5Cr steel in a magnetically driven autoclave with a simulat-ed oilfield produced water at different temperatures and pressures was assessed by means of XRD,SEM and EDS as well as electrochemical measurement and wire beam electrode(WBE)technique.The re-sults show that with the increasing temperature,the corrosion potential of the electrode as a whole has different degrees of negative shift,the corrosion tendency and the corrosion rate of 5Cr steel all increase;meanwhile,the capacitive impedance arc with a large radius emerged in the electrochemical impedance spectrum of 5Cr steel,the film coverage degree and compactness of the corrosion product increase,the charge transfer resistance tends to increase,and the resistance of the electrochemical reaction increases significantly.The formation and expansion of the local anode area on the surface of 5Cr steel has the ten-dency to cause pitting corrosion,which may be preferred to form at defects on the film formed in the early stage of corrosion.The corrosion products are gradually deposited on the inner wall of the pit,then a pro-tective surface layer with obvious Cr enrichment is formed on the inner wall of the pit,thereby,the original pitting corrosion area is transformed from the active sites on the original anode to the cathode area,there-fore,the pitting expansion is inhibited.The polar transformation phenomenon of the corrosion current of the local sites of the 5Cr steel beneath the corrosion product film occurs,namely,from cathodic ones turn to anodic ones,and the defects in the corrosion product film make the 5Cr steel substrate corroded,re-sulting in the appearance of anodic current.
5Cr SteelCO2corrosionhigh temperature and high pressure electrochemistryelectro-chemical impedance spectroscopywire beam electrode
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