油气管道上单纯凹坑缺陷的应变评估研究

发布时间：2018-05-02 23:49

本文选题：管道凹坑 + 轮廓拟合　；参考：《西南石油大学》2015年硕士论文

【摘要】：石油和天然气作为可被大量发掘利用的能源,早已成为国家工业体系的血液,为社会各行各业的发展提供了力量。管道运输以其合理利用地下空间、密闭输送、经济环保等优势,逐步成为石油和天然气的主流运输方式。管道运输的安全问题直接关系到能源安全和生命财产安全,需要引起足够的重视。凹坑是管壁受外部挤压或碰撞而产生径向位移形成的缺陷,属于管道机械损伤的一种,它引起的应力和应变集中对管道的安全运行造成了极大地威胁,因此需要对凹坑缺陷进行合理的评价,及时维修和替换损伤严重的管段。本文针对凹坑缺陷的应变评估进行了以下几方面的研究：首先,整理和归纳了油气管道上凹坑缺陷的分类原则、常见类型、检测方式和现有的评估标准,介绍了ASMEB31.8中凹坑缺陷应变评估的具体方法。其次,在对管道凹坑缺陷的材料非线性和几何非线性等分析基础上,建立了平滑型凹坑和曲折型凹坑的有限元模型,得到两种凹坑缺陷的应变分布规律,以及凹坑缺陷在内压作用下发生回弹的应变变化规律。然后,针对现有的应变评估标准做了一系列的改进研究。第一,在内检测数据到应变求解的过程中,缺少噪声消除和轮廓拟合的相关方法。本文提出了采用四阶B-样条最小二乘拟合算法将检测数据进行噪声消除和轮廓拟合,建立了从含有噪声的检测数据到应变求解的轮廓描述模型。第二,提出采用弧长法计算薄膜应变,同时,考虑管道圆柱壳体的几何特点,改进了标准中等效应变的计算方法。将改进的凹坑缺陷应变计算结果、标准计算结果和有限元结果对比,结果显示改进的应变计算模型大大提高了计算精度。第三,采用断裂力学和损伤力学的相关理论,建立了管道凹坑缺陷韧性损伤模型,分析了两种凹坑类型不同区域的损伤程度、管规格对凹坑损伤的影响以及不同内压下的凹坑缺陷损伤程度,得出不同内压下临界失效应变的拟合关系式,为应变评估时许可应变的拟定提供依据。最后,在凹坑缺陷应变计算模型和韧性失效损伤模型的基础上,提出了包含在线检测、缺陷轮廓描述、应变求解和许可应变选取的基于应变的凹坑缺陷评估流程,并且针对约束型和非约束型凹坑分别采用不同的应变标准。对兰成渝管线广元至江油段检测到的凹坑缺陷进行应变评估,工程评估结果显示该流程能够满足工程实际且具有较高的可操作性,同时评估结果能够为安排开挖维修顺序提供指导。
[Abstract]:Oil and natural gas as a large number of energy can be exploited, has become the blood of the national industrial system, for the development of various sectors of society to provide power. Pipeline transportation has gradually become the mainstream transportation mode of oil and natural gas due to its advantages of rational use of underground space, airtight transportation, economic and environmental protection, etc. The safety of pipeline transportation is directly related to the safety of energy and life and property. Pit is the defect of radial displacement caused by external extrusion or collision of pipe wall. It belongs to one kind of pipeline mechanical damage. The concentration of stress and strain caused by it poses a great threat to the safe operation of pipeline. Therefore, it is necessary to evaluate the defect of pit and repair and replace the damaged section in time. In this paper, the strain assessment of pit defects is studied in the following aspects: Firstly, the classification principles, common types, detection methods and existing evaluation standards of pit defects on oil and gas pipelines are summarized and the concrete methods for evaluating pit defects strain in ASMEB31.8 are introduced. Secondly, based on the analysis of material nonlinearity and geometric nonlinearity, the finite element models of smooth and zigzag concave are established, and the strain distribution laws of two kinds of pitches are obtained. And the strain variation law of rebound under the action of internal pressure of pit defect. Then, a series of improved researches are made on the existing strain assessment criteria. First, there is a lack of relevant methods for noise elimination and contour fitting in the process from the inner detection data to the strain solution. In this paper, a fourth-order B-spline least square fitting algorithm is proposed to remove the noise and fit the contour of the detected data, and a contour description model from the noise detection data to the strain solution is established. Secondly, an arc length method is proposed to calculate the strain of thin film. At the same time, the calculation method of standard medium effect variation is improved taking into account the geometric characteristics of cylindrical shell. The results of improved pit defect strain calculation, standard calculation and finite element analysis show that the improved strain calculation model greatly improves the accuracy of the calculation. Thirdly, based on the theory of fracture mechanics and damage mechanics, the ductile damage model of pipe pit defects is established, and the damage degree in different regions of two types of pits is analyzed. The influence of pipe specification on pit damage and the degree of defect damage under different internal pressure are obtained. The fitting formula of critical failure strain under different internal pressure is obtained, which provides a basis for the determination of allowable strain in strain assessment. Finally, based on the calculation model of pit defect strain and the model of ductile failure damage, an evaluation process based on strain is proposed, which includes on-line detection, description of defect profile, strain solution and selection of allowable strain. Different strain standards are adopted for constrained and unconstrained pits. The strain assessment of the pit defects detected in the Guangyuan to Jiangyou section of the Lancheng Chongqing pipeline shows that the process can meet the practical needs of the project and has a high maneuverability. At the same time, the evaluation results can provide guidance for the order of excavation and maintenance.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE973

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