N80油套管钢应力状态下的CO2腐蚀行为研究

利用交流阻抗技术研究了拉伸、压缩和弯曲三种应力状态下N80油套管钢在饱和CO₂地层水中的腐蚀过程. 结果表明, 三种状态下的阳极电化学阻抗谱均出现了高频容抗弧、中低频感抗弧和低频容抗弧三个时间常数, 其中高频容抗弧与双电层电容和传递电阻有关, 感抗弧对应膜的活性溶解, 低频容抗弧与试样表面膜的生成有关. 随着三种状态下应变的增加, 感抗弧逐渐扩大, 而低频容抗弧则逐渐缩小, 表明应力状态下N80钢的CO₂腐蚀会加剧. 三种状态下的阴极阻抗谱高频均由容抗弧组成, 中低频由Warburg阻抗和容抗弧共同组成, 三种状态下随着应变程度的增加, Warburg阻抗增加, 反应电阻减小, 双电层电容减小, 说明应力会加速阴极反应过程的进行, 从而增加N80钢的CO₂腐蚀速率.

Investigation on CO2 Corrosion Behaviors of N80 Tubing Steel Under Stress Conditions

The CO2 corrosion behavior of N80 steel in stratum water with saturated CO2 under tension,compression and bending stress conditions,was investigated by electrochemical impedance spectra. The re-sults showed that the anodic impedance spectra under the three stress conditions all consisted of three time-constants,i.e.,the capacitance at high frequency,inductance at middle frequency and capacitance at low frequency,among which the frequency at high frequency and the capacitance of the double-layer were related to the transfer impedance,the dissolution of N80 steel contributed to the inductance,and the capaci-tance at low frequency was corresponding to the formation of corrosion film on N80 surface. With the stress increment,the inductance increased,and the capacitance at low frequency decreased,meaning that the an-odic reaction rate increased under the stress conditions. The cathodic impedances under the three stress con-ditions all consisted of capacitance at high frequency,Warburg impedance and capacitance at middle and low frequencies,and with the increment of strain under the three stress conditions,the Warburg impedance increased,while the reaction impedance and the capacitance of double-layer decreased,meaning that the CO2 corrosion may be accelerated when N80 steel is under the stress conditions.