高pH值完井液中钛合金管材的腐蚀行为研究

基于高温高压腐蚀速率和原位电化学测试,并结合分子动力学模拟和第一性原理计算,探讨了钛合金(TC4)管材在高pH值完井液中的腐蚀行为,以及钝化膜的热力学稳定性。结果表明:TC4钛合金在180℃的高pH值磷酸盐完井液中的腐蚀极为严重,其均匀腐蚀速率高达0.4429mm/a;在高pH值磷酸盐完井液中,TC4钛合金的腐蚀为阳极反应过程控制,随着温度的升高,其腐蚀电位、腐蚀产物膜的膜阻和极化电阻显著降低,腐蚀反应的热力学驱动力增大、动力学阻力降低,腐蚀电流密度显著升高;在碱性溶液中,TiO_2钝化膜的钛氧键发生不同程度断裂,并且随着温度升高、碱性增强,TiO_2与溶液的界面结合能逐渐增大,钝化膜的热力学稳定性明显降低;在碱性焦磷酸钾溶液中,TiO_2钝化膜均可与K_2HPO_4、K_3PO_4反应生成疏松多孔的KTiOPO_4腐蚀产物膜,但TiO_2与K_3PO_4反应的热力学倾向更大。

Corrosion behavior of titanium alloy OCTG in high pH value completion fluid

Based on the high temperature and high pressure corrosion tests, the corrosion behavior of titanium alloy OCTG (oil country tubular goods) in high pH value completion fluid was studied by in-situelectrochemical measurement, the stability of titanium alloy passivation film was investigated by molecular dynamic simulation of thermodynamic, and the reaction enthalpy was calculated by using first-principles method. The results show the corrosion of TC4 alloy in high pH value phosphate completion fluid is very serious, and the uniform corrosion rate is as high as 0.4429 mm/a.The corrosion reaction of TC4 alloy in high pH value phosphate completion fluid is controlled by anodic reaction process.With the increase of temperature, the corrosion potential, the film resistance of corrosion product scale and the polarization resistance decrease significantly, the thermodynamic driving force of corrosion reaction increases, while the dynamic resistance decreases, and the corrosion current density of TC4 alloy increases significantly. In TiO₂ passivation film, the titanium-oxygen bonds of TiO₂ is tending to break due to the immersion of alkaline solution. Furthermore, the interfacial bonding energy between TiO₂ and aqueous solution increases gradually with the increasing of temperature and alkalinity, so the thermodynamic stability of passivation film decreases. In alkaline potassium pyrophosphate solution, TiO₂ passivation film can react with K₂HPO₄ and K₃PO₄ to form porous KTiOPO₄ corrosion product scale, but the thermodynamic tendency of the reaction between TiO₂ and K₃PO₄ is more obvious.