温度对N80钢在饱和CO_(2)模拟地层水下腐蚀行为的影响及机理

Effect and Mechanism of Temperature on the Corrosion Behavior of N80 Steel in Simulated Formation with Saturated CO_(2)

目的研究N80钢在饱和CO_(2)模拟油田地层水中于不同温度下的腐蚀行为及腐蚀特征,探究N80钢在饱和CO_(2)模拟油田地层水中的腐蚀规律及机理。方法利用高温高压釜对N80钢在不同温度(60、90、120℃)的饱和CO_(2)模拟油田地层水中浸泡96 h的失重腐蚀进行测试,并用电化学分析仪对其进行相同条件下的宏观电化学测试。采用XRD、SEM、EDS对N80钢腐蚀后的腐蚀产物物相结构、表面形貌、元素组成及腐蚀产物去除后基体表面的腐蚀形貌进行分析。结果N80钢在饱和CO_(2)模拟油田地层水中所形成的腐蚀产物主要由FeCO_(3)和溶液介质中的结晶盐CaCO_(3)组成。温度影响腐蚀产物膜的形貌特征、晶粒尺寸及其致密度变化,导致基体发生不同程度的腐蚀。60℃时,表面生成的腐蚀产物膜均匀覆盖于基体表面,产物膜膜层平整、致密,去除腐蚀产物后,表面有少量点蚀坑;温度升至90℃时,基体表面覆盖的腐蚀产物凹凸不平,晶粒粗大,排列较乱,规则性差于60℃下的腐蚀产物,腐蚀产物去除后,发现基体表面有大片蚀坑群,发生连片腐蚀;120℃时,腐蚀产物晶粒减少,覆盖不均,具有明显蚀孔和裂纹,部分腐蚀产物脱落,去除腐蚀产物后的基体表面出现大面积蚀坑,发生严重腐蚀。N80钢的腐蚀速率由60℃时的0.0210 g/(m^(2)·h)增至90℃时的0.0360 g/(m^(2)·h),至120℃时的0.0444 g/(m^(2)·h)。N80钢的自腐蚀电流密度由60℃时的1.3623×10^(-6)A/cm^(2)增至90℃时的1.4273×10^(-6)A/cm^(2),至120℃时的1.7851×10^(-6)A/cm^(2),但其自腐蚀电位则随温度的增加而减小。结论随腐蚀温度增加,N80钢表面所生成的腐蚀产物膜变得较疏松,且膜层含较多微孔与裂纹,腐蚀速率持续增加,N80钢腐蚀加重。

The corrosion behavior and corrosion characteristics of N80 steel under the different temperature condition in the simulated oilfield formation water with saturated CO_(2)are studied,and its corrosion law and mechanism are explored.The change of the morphology,grain size and density of the corrosion product film occurred because of the temperature.The change furtherly caused the different degrees of corrosion of the substrate.At the temperature of 60℃,the surface of the substrate is evenly covered by the corrosion product film,and the film is flat and dense.A few pits appeared on the surface of the substrate when the corrosion products are cleaned off.When the temperature increases to 90℃,the corrosion products covered on the surface of the substrate are uneven.The crystal grains are coarse and their arrangement is chaotic.The regularity is worse than that of the corrosion products at 60℃.After the corrosion products are removed,large groups of corrosion pits occurs on the surface of the substrate and it occurs the sheet corrosion.At the temperature of 120℃,the grains of the corrosion products reduce.The coverage of film is uneven and it has obvious pits and cracks.Moreover,some of the corrosion products fall off.After the corrosion products are removed,a large area of corrosion pits occurs on the surface of N80 substrate,which showing the substrate with severe corrosion.The corrosion rate of N80 steel increases from 0.0210 g/(m^(2)·h)at 60℃to 0.0360 g/(m^(2)·h)at 90℃to 0.0444 g/(m^(2)·h)at 120℃.The self-corrosion current density of N80 steel increases from 1.3623×10^(‒6)A/cm^(2)at 60℃to 1.4273×10^(‒6)at 90℃,and then to 1.7851×10^(‒6)A/cm^(2)at 120℃.However,the self-corrosion potential decreases with the increase of the temperature.As the temperature rising,the corrosion product film gradually becomes loose,more porous and cracks,and the corrosion rate continues to increase.Therefore,the corrosion degree of N80 steel aggravated.