油气开采用钛合金石油管材料耐腐蚀性能研究

An Investigation of Anti-corrosion Properties of Titanium Alloy OCTG Used in Oil and Gas Exploration

摘要:

钛合金因为具有高强低密、低弹性模量、优异的韧性、疲劳性能和耐蚀性,已经成为严酷工况环境下油井管和海洋开发工具的热门可选材料。由于我国油气开发工况更为恶劣,部分钛合金材料制备的油井管在服役时会发生一定的腐蚀问题,特别是缝隙腐蚀问题最为明显,严重者会导致钛合金油井管在服役过程中的接头密封失效而带来巨大的经济损失。本文选取5种油气开常用钛合金材料(Ti-6Al-4V、Ti-6Al-4V-0.1Ru、Ti-6Al-2Sn-4Zr-6Mo、Ti-3Al-8V-6Cr-4Zr-4Mo和Ti-5.5Al-4.5V-2Zr-1Mo)为研究对象,使用高温高压釜模拟国内典型严酷服役工况环境,研究了不同钛合金材料耐均匀腐蚀、局部腐蚀、点蚀、应力腐蚀开裂及缝隙腐蚀的性能,通过使用扫描电镜和能谱分析等手段对腐蚀形貌和腐蚀产物进行了分析,并使用电化学方法对不同合金的耐腐蚀机理进行了研究。结果显示,在所测试工况条件下,所有钛合金材料腐蚀反应均为阳极控制过程,均匀腐蚀速率均低于0.001mm/a,并且对应力腐蚀开裂均有良好的抗力。Ti-6Al-4V和Ti-5.5Al-4.5V-2Zr-1Mo合金出现明显的点蚀和缝隙腐蚀问题。对腐蚀机理研究表明,在工况条件温度下,随着pH值的降低,所有钛合金均发生的自腐蚀电位降低,极化电阻减小,腐蚀电流增大,耐腐蚀性能下降,其中Ti-6Al-4V耐腐蚀性能下降的最为明显,研究结果为油气开发工况下钛合金石油管的选材和缝隙腐蚀问题防治提供理论基础。

Abstract:

Stem from its high specific strength, low density, low elastic modulus, excellent toughness, fatigue and corrosion resistance, titanium alloy has become a kind of attractive candidate material for oil country tubular goods(OCTG) and offshore components in harsh service environment. Because the oil gas exploration environment of China is more rigorous, certain titanium alloy OCTG will occur corrosion problems especially crevice corrosion, in this service environment, which will lead to the seal failure of titanium alloy OCTG premium connection and cause huge economic losses. In this paper, 5 kind typical titanium alloys materials((Ti-6Al-4V, Ti-6Al-4V-0.1Ru, Ti-6Al-2Sn-4Zr-6Mo,Ti-3Al-8V-6Cr-4Zr-4Mo and Ti-5.5Al-4.5V-2Zr-1Mo))used for oil gas exploration were investigated, the influence of different alloy compositions on anti-corrosion properties of these titanium alloys in China typical service environment were studied by high-temperature high-pressure autoclave simulation test, the corrosion morphology and corrosion products were also analyzed is analyzed and summarized by using scanning electronic microscopy (SEM)and energy dispersive spectrometer (EDS),the corrosion resistance mechanism of different alloys was discussed by electrochemical method. The results showed that the corrosion reactions of all titanium alloy materials were anode controlled under the test conditions, the uniform corrosion rates of all tested titanium alloy were lower than 0.001mm/a, and the resistance to stress corrosion cracking of all titanium alloys were excellent. However, Ti-6Al-4V and Ti-5.5Al-4.5V-2Zr-1Mo alloys had obvious pitting and crevice corrosion problems. The corrosion mechanism results showed that, under the test conditions, the self-corrosion potential, polarization resistance of all titanium alloys decreased and the corrosion current increased with the decrease of pH value, which illustrated that corrosion resistance of titanium alloys were reduced, especially for Ti-6Al-4V. The research results provide a theoretical basis for material selection and crack corrosion prevention of titanium alloy OCTG used in oil and gas exploration.