【作者】 张伯君；

【导师】 苏义脑； 郑津洋； 刘鹏飞；

【作者基本信息】 浙江大学 ， 化工过程机械， 2013， 博士

【摘要】 随着全球经济的快速发展和工业化进程的不断加快,世界各国对天然气和石油等能源的需求量日益增加。埋地管道因为在长距离输送的效率和经济性方面具有明显优势,目前已经成为该类介质的重要输送手段。长输埋地管道跨越的地域范围很广,由于各地区的地质环境复杂多变,管道在服役过程中不可避免的会受到来自周边环境的潜在威胁。近年来,随着地质灾害和极端天气数量的增多,由于山体滑坡引起的管道失效事故不断发生。现阶段,学术界和工程界都在关注两个问题：即如何准确预测山体滑坡作用下埋地管道的极限承载能力,以及判断已发生偏移的管道是否依然能够安全运行。为了解决以上两个问题,本文在两项国家质检公益性行业科研专项课题(项目编号：200910096-2和201210242)的资助下,对山体滑坡作用下埋地管道的强度失效模式开展深入研究,主要的研究内容和成果如下(1)在考虑材料、几何和接触非线性的基础上,建立了山体滑坡区域内埋地管道发生偏移的全过程仿真模型。模型中的滑坡过程采用位移载荷控制,施加位置选择在距离管道不远的土体表面上；管道与土体之间采用有限滑移接触属性模拟两者介面上的相互作用；管道力学性能采用真实的应力.应变曲线描述,并遵循Bridgman方法进行修正以保证计算结果的准确性。(2)基于弹塑性力学理论,运用弧长法和非线性稳定算法预测了山体滑坡作用下管道进入塑性垮塌和应变软化阶段的承载能力,获得了不同偏移程度下埋地管道的力学响应。文中分析了各类参数包括内压、径厚比、滑坡区宽度、土体性能以及管材性能对管道自由偏移能力的影响,指出管道进入塑性垮塌阶段时的最大主应变只与管材和土体的性能有关,该应变可以作为工程许用应变的选取依据之一。(3)基于弹塑性断裂力学理论,运用扩展有限元技术,通过材料试验模拟、无偏移直管爆破模拟和山体滑坡区域内偏移管道的断裂过程模拟三个层面,描述了不同载荷工况下管道材料上的裂纹从萌生、扩展直至断裂的整个过程。首先,通过网格敏感性分析得到了裂尖区域附近单元的临界尺寸；接着,探讨了初始损伤的最大主应力和临界能量释放率对管道上的裂纹特征和力学响应带来的影响,指出前者主要控制材料何时发生损伤,后者主要控制材料发生损伤后何时扩展和最终断裂；最后,通过对内压、径厚比、滑坡区宽度、土体性能以及管材性能等关键参数的分析,得到了裂纹发生扩展和管道最终断裂时的最大主应变。考虑到该应变同样只与管材和土体的性能有关,故将其作为工程许用应变的另一选取依据。(4)提出了基于应变判断的山体滑坡区域内埋地管道的强度失效准则,并结合有限元计算结果和相关国外标准,给出了适合于我国的埋地管道工程许用应变的选取方法。分析时将管道分为无缺陷和含缺陷两类：对于无缺陷管道,其许用应变参考塑性垮塌时的应变、最终断裂时的应变和ASME B31.8的极限应变给出;对于含缺陷管道,本文给出了XFEM和API579两种评价方法的对比结果。(5)以近期我国某地区因山体滑坡引起的管道事故为案例背景,通过材料性能检测、断口分析测试和现场地质勘测,验证本文中提出的有限元模型和工程可接受准则的合理性,为我国今后的埋地管道设计和基于风险的检测工作提供技术支撑。更多还原

【Abstract】 With the development of global economy and industrialization process, demand for resources such as natural gas and oil grows rapidly around the world. At present, buried pipes have become one of the significant ways to transport these resources from remote area for the advantages of high transport and economic efficiency. Because the long-distance buried pipes have to pass through vast territory with complex geology, it will inevitably suffer from the adverse effects from surrounding environment. With increasing frequency of geological disaster and extreme weather, accidents of buried pipes caused by landslide, which is one of the typical permanent ground deformation actions, has roused wide attention in recent decades. So far, there are two significant problems that are urgent to be solved in the academics and engineering:the first one is how to predict the limit load-bearing ability of buried pipe caused by landslide actions accurately and effectively; the second one is to evaluate whether the buried pipe that suffers from deflection load during landslide process can still service in safety without substitution.In order to solve the two problems mentioned above, research on the strength behavior of buried pipes under landslide action is given in this paper. This paper is supported by two special funds for quality supervision research in the public interest (Grant No.200910096-2and201210242). The main contents are given as follows:(1) A3D numerical model is established to predict the mechanical and deformation response of buried pipe due to deflection during landslide process. In the model, the nonlinear effects of material, geometry and contact problems are comprehensively considered. First, the external loads arising from the deformed soil during landslide process are controlled by deflection displacement, and the loading location is applied on the surface of surrounding soil that is close to the buried pipe; Second, the contact pairs with finite sliding property is used to simulate the interaction between the pipe and soil. Third, the true stress-strain curve of pipe material is corrected properly according to the Bridgman law, which ensures the accuracy of finite element analysis.(2) Based on the theory of elastic-plastic mechanics, the limit load-bearing ability of buried pipes under landslide action is predicted using the arc-length algorithm and non-linear stabilization algorithm, and the stress-strain responses of buried pipe at plastic collapse and strain softening stages are obtained. Besides, effects of internal pressure, D/t ratio, width of landslide, mechanical properties of soil and pipes on the flexible deflection ability are investigated. It is revealed that the maximum value of1st principle strain only depends on the mechanical properties of soil and buried pipe when the structure comes into the plastic collapse stage. Thus, this strain can be used as a reference value to determine the allowable strain in engineering later.(3) Based on the theory of elastic-plastic fracture mechanics, the whole fracture process of buried pipe such as crack initiation and propagation under complex loads are demonstrated using the extended finite element method. The simulation contents include:(a) material performance tests of tensile and three-point bending;(b) Burst tests of straight pipe without deflection;(c) Fracture process of buried pipe due to deflection arising from landslide actions. According to the finite element analysis, some conclusions can be obtained:First, the limit value of mesh size near the crack-tip field is obtained which can ensure the computational efficiency and accuracy; Second, σmaxps and Gc are two significant parameters to affect the crack behavior and limited load-bearing ability of buried pipes. The former one represents great influence on the damage initiation property, while the latter one mainly controls the fracture toughness to resist crack propagation; Third, effects of internal pressure, D/t ratio, width of landslide, performances of soil and pipes on the crack behaviors are also investigated. Finally, the values of1st principle strain as crack propagates unstably and pipeline fractures are obtained. Since the two strains only depend on the mechanical properties of soil and buried pipe, they can be used as another reference values to determine the allowable strain later. (4) A common strength failure criterion based on the1st principal strain is proposed to determine the safe properties of buried pipeline under this special failure issue. In the criterion, the value of allowable strain is determined by the results of finite element analysis and limited values in the corresponding standards. For the buried pipe without defects, the allowable strain is given by the strain as buried pipe comes into plastic collapse stage, the strain as buried pipe ultimate fractures, and the strain constrained in the ASME B31.8standard. For the buried pipe with crack-like defects, the results evaluated by XFEM and FAD in API579standard are compared.(4) A typical accident of buried pipeline arising from landslide actions is used to verify the finite element model and strength failure criterion provided in this paper. The contents of failure analysis consist of the base metal/welding mechanical testing, fractographic testing and site inspections, which can provide technical support for the design and risk-based inspection of buried pipes.更多还原