油水两相界面处缓蚀剂的作用效果及机理

Inhibition effect and mechanism of corrosion inhibitor at oil-water interface region

利用旋转圆柱电极,结合电化学方法(电化学交流阻抗、极化曲线)、激光扫描共聚焦显微镜、扫描电子显微镜和紫外-可见分光光度法研究了流动工况下油水分层介质中缓蚀剂在油水两相界面处的作用效果及机理.结果表明,该工况下,100 mg·L-1十七烯基胺乙基咪唑啉季铵盐缓蚀剂对碳钢在油水两相分层介质中的水区具有良好的缓蚀效果,缓蚀效率高达99%,但在油水两相界面区域,由于油相的大量存在,导致缓蚀剂的有效质量分数降为混合前的31%,缓蚀效率仅为83%,缓蚀效果较差,碳钢腐蚀未得到有效抑制,甚至出现了沟槽腐蚀.因此,在油区试样腐蚀轻微,并且缓蚀剂的加入有效抑制了水区X65钢的腐蚀.

With the development of offshore oil and gas fields,the oil–water two-phase mixing flow-transmission technology has been widely used in subsea pipelines.The high water cut and multiphase flow regime induce harsh and complex corrosion conditions;hence,mild steels combined with corrosion inhibitors are used in the construction of offshore pipelines for corrosion control.However,corrosion failure cases show that severe localized corrosion constantly occurs at the oil–water interface in oil–water mixed transmission pipelines,and the understanding of the mechanism and inhibition effect of corrosion inhibitors is limited.Moreover,laboratory studies on CO2 corrosion problems in oil–water mixed transmission pipelines usually consider only pure-water systems to simulate the corrosive environment.These studies seldom regard the effect of the oil phase on the corrosion process even though the actual production and transportation of fluids often involves multiphase mixed media.The oil phase is one of the important factors that affect corrosion behavior.Studies on the impact of the oil phase on the inhibition effect of corrosion inhibitor are still relatively lacking.Further studies on the inhibition effect of corrosion inhibitor in oily corrosive environments of oil–water mixed transmission pipelines are needed.In this study,the inhibition effect and mechanism of a corrosion inhibitor at the oil–water two-phase interface under flow conditions were investigated using the rotating cylindrical electrode(RCE)technique combined with electrochemical methods(electrochemical impedance spectroscopy and polarization curve analysis),laser scanning confocal microscopy,scanning electron microscopy,and UVVIS spectrophotometry.The results reveal that 100 mg·L-1 of seventeen alkenyl amide ethyl imidazoline quaternary ammonium salt as a corrosion inhibitor in carbon steel for an aqueous phase of the oil–water two-phase stratified medium exhibits significant inhibition effect,and the corrosion inhibition efficiency reachs 99%.However,the effective mass fraction of the corrosion inhibitor decreases to31%before mixing at the oil–water interface because of the presence of oil.As a result,the corrosion inhibition efficiency is only 83%,and the inhibition effect is poor;moreover,the corrosion of carbon steels cannot be effectively controlled.Further,significant groove corrosion is observed at the oil–water interface.Therefore,the corrosion of the sample in the oil area is slight,and the inhibitor can effectively inhibit the corrosion of X65 steel in the water area.