高含硫环境下镍基合金腐蚀行为研究

发布时间：2018-05-21 19:00

本文选题：镍基合金 + 单质硫　；参考：《西南石油大学》2017年硕士论文

【摘要】：镍金合金由于其优异的耐腐蚀性能而被广泛地应用于酸性油气田,在酸性气井的开发过程中,由于元素硫的析出沉积会产生严重的局部腐蚀,使得镍基合金在服役过程中经受严峻的考验。因此针对硫对镍基合金的腐蚀行为,研究硫沉积腐蚀发生的根本原因,正确认识元素硫所引起的局部腐蚀机制是高含硫气田开发过程中必须要解决的问题。本论文参照国内外关于硫腐蚀研究成果,通过研究不同硫状态下镍基合金的腐蚀行为,探究高含硫环境下的腐蚀规律和局部腐蚀机制,以期为高含硫油气生产输送时的腐蚀与防护提供理论参考。本文首先对镍基合金825在模拟不同温度高含H2S/CO2及不同状态单质硫条件下的腐蚀规律以及腐蚀行为特征进行了研究。结果表明,温度和硫状态是影响镍基合金825腐蚀行为的重要因素;在温度较低条件下,镍基合金825的腐蚀轻微表现出均匀腐蚀的特征,随着硫状态的变化腐蚀速率发生小幅的增大;当温度升高到90℃时,镍基合金825的腐蚀速率升高,出现明显的点蚀现象表现出局部腐蚀的特征;随着腐蚀时间的延长,蚀坑逐渐增大,熔敷硫状态下的合金尤为明显,出现了晶间腐蚀裂纹。在温度升高的条件下,腐蚀介质中的硫的活性增大,镍基合金825产物膜的稳定性随着温度的升高而逐渐减弱,使得腐蚀速率逐渐增大。对高温不同硫状态条件下腐蚀后的镍基合金825进行X射线衍射(XRD)分析表明,在温度较低的情况下,在无单质硫条件和熔敷条件下产物膜主要是Cr203,而悬浮硫情况下由于硫的沉积使得基体表面出现了硫化物;当温度升高到90℃时,在无单质硫条件下产物膜成分仍为Cr203,但是衍射峰峰高降低,温度升高使得产物膜稳定性下降;在悬浮硫和熔敷硫条件下镍基合金825腐蚀产物膜的结构由硫化物和氧化物组成,膜层结构由氧化物向硫化物的转变,成为镍基合金825腐蚀加深加重的主要原因,特别是熔敷硫条件下由常温条件下的均匀腐蚀转变成了局部腐蚀。其次,对在模拟不同温度高含氏H2S/CO2及不同状态单质硫条件下腐蚀后的镍基合金825进行了极化曲线、交流阻抗测试及扫描电化学显微镜(SECM)测试,结果与宏观腐蚀所得结果基本一致。极化曲线结果表明,在温度升高及硫状态变化的条件下,镍基合金825表面自腐蚀电流密度随之发生显著增大,钝化区间相应变窄,由钝化溶解逐渐转化为活性溶解,钝化膜稳定性下降,保护性能变差。交流阻抗曲线的拟合结果也表明,在温度升高及硫状态变化的情况下,双电层电容有升高的趋势,使得极化电阻减小,活性离子穿过钝化膜所产生的阻力下降,保护性能降低,硫的加入使得合金表面稳定性明显减弱。SECM结果表明,在硫状态变化和温度升高的条件下,镍基合金825基体表面的活性增强,基体表面的电流峰峰高和峰频增大,点蚀敏感性升高,抗腐蚀能力下降。最后,对镍基合金825进行了晶界工程处理,通过电子背散射衍射(EBSD)分析表明,退火后的镍基合金825特殊角度晶界比例明显提高。镍基合金825特殊角度晶界∑3、∑9、∑27等随机分布在一般大角度晶界构成的晶界网络上,破坏原有的晶界网络的连通性,有效阻断材料沿晶界的腐蚀开裂以及其他失效形式的扩展,从而使得镍基合金825在高含硫环境下的抗腐蚀能力增强。通过极化曲线、交流阻抗曲线和扫描电化学显微镜分析发现晶界工程处理过后的镍基合金825具有更好的耐蚀性和更低的点蚀敏感性。
[Abstract]:Nickel gold alloys are widely used in acid oil and gas fields because of their excellent corrosion resistance. In the process of developing acid gas wells, the precipitation of elemental sulfur will produce serious local corrosion, which makes nickel base alloys undergo severe tests during service. Therefore, the sulfur deposition of sulfur on nickel base alloys is studied. The root cause of corrosion and the correct understanding of the local corrosion mechanism caused by elemental sulfur are the problems that must be solved in the development of high sulfur gas fields. In this paper, the corrosion behavior of nickel based alloys under different sulfur States is studied by reference to the results of sulfur corrosion research at home and abroad, and the corrosion laws and local decay in high sulphur environment are explored. Corrosion mechanism is expected to provide a theoretical reference for corrosion and protection of high sulphur oil and gas production and transportation. The corrosion law and corrosion behavior characteristics of nickel base alloy 825 under the condition of simulating different temperatures and high H2S/CO2 and different state sulfur are studied. The results show that temperature and sulfur state are the 825 corrosion of nickel base alloy. Under the low temperature conditions, the corrosion of nickel base alloy 825 slightly showed the characteristic of uniform corrosion, and the corrosion rate increased slightly with the change of sulfur state. When the temperature rose to 90, the corrosion rate of the nickel base alloy 825 increased, and the obvious pitting phenomenon showed the characteristic of local corrosion. The corrosion crater increases gradually, and the alloy under the state of the deposited sulfur is particularly obvious, and the intergranular corrosion cracks appear. The sulfur activity in the corrosion medium increases with the temperature rising. The stability of the 825 product film of the nickel base alloy gradually decreases with the increase of temperature, which makes the corrosion rate increase gradually. The X ray diffraction (XRD) analysis of the nickel base alloy 825 after corrosion shows that under the condition of low temperature, the product film of the product is mainly Cr203 under the condition of no single sulfur and cladding, while the sulfur deposition makes the sulfide on the surface of the matrix under the condition of suspended sulfur, and when the temperature rises to 90, the product under the condition of no single sulfur is under the condition of the temperature rise. The composition of the membrane is still Cr203, but the peak height of the diffraction peak decreases and the temperature increases, the stability of the product film decreases. The structure of the 825 corrosion product film of the nickel base alloy is composed of sulfide and oxide under the suspended sulfur and the deposited sulfur, and the main reason for the aggravation of the 825 corrosion of the nickel base alloy is that the structure of the film is changed from oxide to sulfide. Second, the polarization curve, AC impedance test and scanning electrochemical micromirror (SECM) test are carried out for the nickel base alloy 825 after corrosion at different temperatures with high H2S/CO2 and different state elemental sulfur conditions, and the results are with macro corrosion. The results of polarization curves show that the corrosion current density of the 825 surface of Ni based alloy increases significantly at the temperature rise and the change of the sulfur state, and the passivation interval becomes narrower, and the passivation solution is gradually converted to active dissolution. The stability of the passivation film decreases and the protection performance becomes worse. The fitting result of the AC impedance curve is the result of the passivation film. It is also shown that in the case of temperature rise and the change of sulfur state, the electric double layer capacitance is rising, the polarization resistance decreases, the resistance of active ions passing through the passivation film decreases and the protection performance is reduced. The addition of sulfur makes the surface stability of the alloy weaken obviously.SECM results show that the condition of the change of sulfur state and the temperature increase. At the same time, the activity of the nickel base alloy 825 substrate was enhanced, the peak current peak and the peak frequency of the matrix increased, the pitting sensitivity increased and the corrosion resistance decreased. Finally, the nickel base alloy 825 was treated with grain boundary engineering. The EBSD analysis showed that the grain boundary ratio of the annealed nickel base alloy 825 was obviously improved. The 825 special angle grain boundary sigma 3, sigma 9, and sigma 27 of the nickel base alloy are randomly distributed on the grain boundary network formed by the general grain boundary, which destroys the connectivity of the original grain boundary network, effectively blocks the corrosion cracking along the grain boundary and the expansion of other failure forms, thereby increasing the corrosion resistance of nickel base alloy 825 in the high sulfur content environment. Strong. Through the polarization curve, AC impedance curve and scanning electrochemical microscopy, it was found that the nickel base alloy 825 after the grain boundary engineering treatment had better corrosion resistance and lower pitting sensitivity.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG178

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