超深井高强度油套管钢环境断裂的细观力学参数表征研究

During the exploration and exploitation of ultra-deep, high pressure, high temperature and high sulfur gas filed, the high-strength steel resistant from sulfur corrosion will have to be used for well construction to avoid disastrous accidents resulting from hydrogen brittleness fracture of tubing and casing. However, there is a problem to be solved urgently, how to evaluate the fracture properties of high-strength steel in the H2S environment. At present, there is not yet quantitative relation between the microstructure of material and its fracture properties, and only experiment study is applied to judge whether it will fracture at specified conditions. This project will firstly set up the constitutive relationship and fracture toughness and tension model of the high-strength steel in the H2S environment according to experiment data. Then, the microstructure information of steel will be observed by the means of Environmental Scanning Electron Microscopy (ESEM) and Transmission Electron Microscope (TEM). With the help of computer image recognition technique and statistics methods, microstructure model will be built up with irregular size and statistical distribution of inclusion and the third phase intercrystalline sediments. Based on the Mesomechanics theory, Representative Volume Element (RVE) of high-strength steel will be built up, which research on the impact with microstructure information to material macroscopic strength and fracture toughness. Applying eXtended Finite Element Method (XFEM) theory, the process of cracking and crack growth of Representative Volume Element RVE) in the H2S environment will be reproduced. Comparative analysis of the results of simulation and experimental data, the representation model of material Mesomechanics parameter to the macroscopic properties will be built up. The result of this project will create a great and direct value to improve performance of anti-sulfur steel properties and form a new method to research on fracture criterion.

“超深三高”气田的勘探开发必须采用高强度抗硫钢油套管建井以避免由于H2S环境断裂造成灾难性事故，如何评价高强度钢环境断裂和开发满足超深井抗硫油套管是当前亟待解决的问题,然而目前只能通过实验判定其断或不断，没有建立材料微观结构与其H2S环境断裂性能的定量关系。本项目首先借助ESEM和TEM研究不同钢材细观结构，建立钢材夹杂物、晶体缺陷和微裂纹的含量、尺寸和不规则分布等参数的统计细观力学模型和细观尺度代表性体积单元力学数学模型；然后应用TEM研究高强度钢慢应变速率拉伸应力腐蚀的细观尺度变化过程，在此基础上开展代表性体积单元在H2S环境断裂数值试验，再现其开裂和裂纹扩展过程，分析影响钢材环境断裂的细观尺寸临界值和分布函数；最后对比分析实验数据和数值模拟结果，建立材料晶体缺陷等细观参数对宏观环境断裂性能的表征模型。研究成果为更高强度抗硫钢研发和形成新的H2S环境断裂判据研究具有重要理论意义。

本项目针对含夹杂物和微裂纹的高强度钢开展了大量宏观、细观实验和数值试验断裂失效研究，认识到了高强度钢夹杂物和微裂纹等细观结构及其在外力作用下影响宏观断裂性能的机理，明确了微裂纹和杂质在考虑氢压的H2S环境的断裂失效过程，建立了细观结构参数与宏观环境断裂性能的关系，为H2S环境高强度钢断裂评价和应用奠定了理论基础。通过项目研究在国内外发表学术文章29篇，其中SCI 收录14 篇，授权发明专利和实用新型专利20件，参与出版专著1部，参加国际学术会议10次，培养硕士5人和博士3人，资助4名研究人员赴国外访问及联合培养。研究成果为更高强度抗硫钢研发和形成新的H2S环境断裂判据研究具有重要理论意义。

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