油套管用Ti6Al4V合金热氧化表面改性及其典型服役行为研究

发布时间：2018-05-20 21:22

本文选题：热氧化 + 钛合金　；参考：《太原理工大学》2016年博士论文

【摘要】：油套管是油气井的重要基础材料,约占整体油井管消费量的四分之三。腐蚀和磨损工况极易导致油套管失效,严重威胁油气井的安全运行。为确保油气田安全、高效地开发与生产,最有效的措施是采用耐蚀合金管材,但耐蚀合金含有价格昂贵的金属元素,大批量使用会使生产成本增加。Ti6Al4V合金比强度高、热稳定性好、耐蚀性优异、生物相容性好,被誉为王牌钛合金,广泛应用于民用和军事领域。目前,已有机构将Ti6Al4V合金-碳钢复合管作为新型套管材料应用于油气开采。以碳钢管材为基体材料,发挥碳钢的良好力学性能和低价优势;以Ti6Al4V合金为内衬,利用其高比强度和优异的耐蚀性,可显著降低原材料采购成本及管道的长期运营成本,具有广阔的应用前景。但是,Ti6Al4V合金导热系数小、摩擦系数大、粘着磨损和微动磨损敏感性高,且表面承载能力低,直接将Ti6Al4V合金作复合管内衬使用将明显影响结构的安全性和可靠性,这也是Ti6Al4V合金作为复合管内衬材料不能回避、也是必须加以考虑的问题。钛与氧的化学亲和性较高,热氧化已被认为是一种能够同时提高钛及钛合金耐磨性和耐蚀性的有效方法。针对Ti6Al4V合金作为复合管内衬材料的工程背景,借助热氧化技术对ti6al4v合金进行表面改性,分别以热氧化温度和热氧化时间为参数,进行了热氧化工艺优化,评价了热氧化层在模拟油田介质中的典型服役行为:冲蚀磨损和腐蚀磨损行为,研究结果可望为拓展ti6al4v合金在石油管材方面的应用提供参考依据。主要研究结果如下:(1)通过研究热氧化温度和热氧化时间对热氧化层的厚度、耐磨性和耐蚀性的影响来优化热氧化工艺,综合评价所获得的优化参数为:热氧化温度973k,热氧化时间30h。在此工艺下制备的热氧化层中的主相为金红石型tio2,热氧化层的厚度超过12μm,表面硬度达868hv。热氧化层由α-al2o3和金红石tio2混晶层+单一金红石型tio2层+tixoy混杂层+o扩散层构成,表现出明显的多层结构特征。(2)对优化参数下所获得的热氧化层分别进行xps分析、截面的硬度和结合强度测试,在co2饱和模拟油田采出液中的mott-schottky曲线,研究热氧化层的半导体特性,探索其耐蚀本质。结果表明:热氧化层的成分呈梯度分布,氧化层至下方基体的硬度分布亦呈梯度,有利于改善材料表面的承载能力和耐磨性能。结合强度测试结果表明,划痕测试中致密贫铝氧化物层和氧的扩散层所对应的临界载荷数值约为6n和10n。ti6al4v合金的mott-schottky曲线可拟合为两段线性特征,且斜率值均为正,表现出n型半导体特性。热氧化层的mott-schottky曲线由两部分组成,段(i)明显的线性特征,且斜率为正,也表现出n型半导体特性;段(ii)呈近线性特征,斜率为负,表现出p型半导体特性。热氧化层的p-n双极性半导体特性既能阻止阳离子从基体中迁移,又能抑制溶液中的阴离子侵蚀基体,使其表现出更好的耐蚀性。(3)在固-液两相流的冲蚀磨损条件下,研究了Ti6Al4V合金和热氧化层的冲蚀磨损行为。固体粒子冲蚀和液相介质腐蚀的协同作用引发了Ti6Al4V合金和热氧化层表面的破坏。低硬度的Ti6Al4V合金的耐冲蚀磨损性能较差,而热氧化层表现出很好的耐冲蚀磨损性能,可以对Ti6Al4V合金起到良好的保护作用,热氧化层在固-液两相流腐蚀介质中优异的冲蚀磨损抗力得益于其表面的高硬度以及其在腐蚀介质中的化学稳定性;(4)Ti6Al4V合金和热氧化层与两种摩擦配副在CO2饱和模拟油田采出液中的腐蚀磨损行为存在差异,该差异在摩擦系数-时间曲线、磨损失重以及磨痕特征中均得到体现。总体上讲,表面热氧化层显著增强了Ti6Al4V合金的抗腐蚀磨损能力。
[Abstract]:Oil and gas casing is an important basic material for oil and gas wells, accounting for about 3/4 of the total oil well pipe consumption. Corrosion and wear conditions are very easy to cause oil and casing failure, which seriously threatens the safe operation of oil and gas wells. In order to ensure the safety of oil and gas fields, the most effective measure is to use corrosion resistant alloy pipes, but the corrosion resistant alloys contain price. The expensive metal elements, which can increase the production cost, increase the production cost of.Ti6Al4V alloy with high strength, good thermal stability, excellent corrosion resistance and good biocompatibility. It is widely used in civil and military fields. At present, Ti6Al4V alloy carbon steel composite tube is used as a new type of casing material in oil and gas exploitation. Carbon steel tube is used as matrix material to give full play to the good mechanical properties and low price advantages of carbon steel. With Ti6Al4V alloy as the inner lining, using its high specific strength and excellent corrosion resistance, the purchase cost of raw materials and the long operating cost of the pipeline can be significantly reduced. However, the thermal conductivity of Ti6Al4V alloy is small, the coefficient of friction is large and the coefficient of friction is big. With high sensitivity to wear and fretting wear, and low bearing capacity of the surface, the direct use of Ti6Al4V alloy as a composite liner will obviously affect the safety and reliability of the structure. This is also a question that Ti6Al4V alloy can not be avoided as a composite liner material. It is also a question that must be considered. It is considered an effective method to improve the wear resistance and corrosion resistance of titanium and titanium alloy at the same time. For the engineering background of Ti6Al4V alloy as a composite tube lining material, the surface modification of Ti6Al4V alloy is carried out with the help of thermal oxidation technology. The thermal oxidation process is optimized and the thermal oxidation process is optimized. The typical service behavior of oxidation layer in simulated oilfield medium: erosion wear and corrosion wear behavior. The results are expected to provide a reference for expanding the application of Ti6Al4V alloy to oil pipes. The main results are as follows: (1) the thickness, wear resistance and corrosion resistance of the thermal oxidation layer are studied by the study of the thermal oxidation temperature and the time of thermal oxidation. The optimum parameters of the thermal oxidation process are optimized: the thermal oxidation temperature 973k, the thermal oxidation time 30h., the main phase of the thermal oxidation layer prepared under this process is rutile TiO2, the thickness of the thermal oxidation layer is more than 12 mu m, the surface hardness of the 868hv. layer is from alpha -al2o3 and rutile TiO2 mixed crystal layer + single rutile. TiO2 layer +tixoy hybrid layer +o diffusion layer, showing obvious multi-layer structure characteristics. (2) XPS analysis of the thermal oxidation layer obtained under the optimized parameters, the hardness and bonding strength of the cross section, the Mott-Schottky curve in the extracted fluid of the CO2 saturated simulated oilfield, the study of the semiconductor properties of the thermal oxidation layer, and the exploration of its corrosion resistance. The results show that the composition of the thermal oxidation layer is gradient distribution and the hardness distribution of the oxide layer below the substrate is also gradient, which is beneficial to improve the bearing capacity and wear resistance of the material surface. The test results show that the critical load corresponding to the dense poor aluminum oxide layer and the diffused layer of oxygen in the scratch test is about 6N and 10n.ti. The Mott-Schottky curve of 6al4v alloy can be fitted with two linear features, and the slope values are all positive, showing the characteristics of N type semiconductors. The Mott-Schottky curve of the thermal oxidation layer is composed of two parts, the segment (I) is obviously linear, and the slope is positive, and the N type semiconductor specificity is also shown. The segment (II) is near linear, and the slope is negative, showing P half. The characteristics of the conductors. The p-n bipolar semiconductor properties of the thermal oxidation layer can not only prevent the migration of the cations from the matrix, but also inhibit the anionic erosion of the matrix in the solution. (3) the erosion wear behavior of the Ti6Al4V alloy and the thermal oxidation layer was studied under the erosion and abrasion conditions of the solid liquid two phase flow. The synergistic effect of the corrosion of liquid phase medium leads to the destruction of Ti6Al4V alloy and the surface of the thermal oxidation layer. The corrosion resistance of low hardness Ti6Al4V alloy is poor, and the thermal oxidation layer exhibits good erosion resistance and wear resistance, which can protect the Ti6Al4V alloy well. The thermal oxidation layer is superior to the solid liquid two-phase flow corrosion medium. The different erosion wear resistance is due to its high surface hardness and its chemical stability in the corrosive medium. (4) the corrosion wear behavior of Ti6Al4V alloy and thermal oxidation layer and two kinds of friction pairs in the production fluid of CO2 saturated simulated oil field is different, and the difference is obtained in the friction coefficient time curve, wear weight loss and wear mark characteristics. Generally speaking, the surface thermal oxidation layer significantly enhanced the corrosion and wear resistance of Ti6Al4V alloy.
【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TE931.2;TG174.451

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