基于磁记忆的油气管道应力损伤检测机理及应用研究

发布时间：2018-08-26 14:59

【摘要】：油气管道运输具有高效率、低成本及安全可靠等优点,是能源运输的重要方式。目前全世界已建成油气输送管道已超过250万公里,而且这个数据每年仍在增长。我国地域辽阔,油气资源分布不均,油气的管道输送成为关乎国民经济和社会发展的重要产业。由于管道具有高能高压、易燃易爆、有毒有害、连续作业、链长面广、环境复杂等特点,决定了管道安全管理的重要性。石油天然气输送管道所应用的钢铁材料具有良好的强度、硬度、塑性和韧性等机械性能以及良好的铁磁性能,其发生破坏将经历由应力集中导致材料屈服进而发生塑性变形再到破坏的过程。管道在建设和使用过程中,会受到各种应力的作用,当管道局部存在缺陷或其他质量问题时,将会在局部产生应力集中,引起局部应力过大,甚至导致管道发生塑性变形或破坏。应力集中是威胁管道安全性的一个重要因素,由应力集中引起的塑性变形损伤被认为是材料的早期损伤。对管道应力集中及塑性变形的有效检测可以预判危害的发生,并可作为评价管道应力集中程度的依据,对保障管道安全意义重大。磁记忆检测方法作为一种应力检测方法已得到行业的认可,它具有设备简单、操作方便、可实现在线大范围无损检测及对设备危险的早期判断等优点。但目前针对磁记忆信号形成的机理及特征尚无统一的定论,还不能明确在各种条件下的检测信号特征。同时由于微弱的磁记忆信号亦受影响,对实验研究方法的有效性具有较高要求,很多实验方法具有一定局限性,不能有效说明磁记忆现象的真实情况,从而导致该方法在一些工程应用中的有效性受到质疑。铁磁材料的磁性来源于原子磁矩,决定于微观电子体系的运动及相互作用状态。本文从量子力学微观理论出发,以密度泛函理论为基础建立铁磁材料力磁耦合磁记忆效应理论模型,通过第一性原理研究了铁磁体系在力磁耦合过程中磁记忆信号特征,对应力损伤的磁记忆信号特征及检测机理进行深入研究。通过拉伸和管道打压实验对理论研究结果进行了验证。并开展了管道应力损伤磁记忆内检测技术的工程应用,对该检测方法的工程应用可行性和有效性进行了研究。论文对铁磁材料的力学和磁学特性进行了研究,明确了铁磁材料应力损伤形成的微观机理及磁性的微观起源。以体系微观电子密度分布函数为基础,建立铁磁材料力磁效应的量子力学密度泛函理论模型,通过第一性原理仿真软件CASTEP计算了正常铁磁晶体结构和塑性变形铁磁晶体结构两种铁磁体系在不同应力作用下的能带结构、电子态密度分布及原子磁矩。理论研究结果表明,铁磁材料在单向拉伸和三向拉伸两种应力状态下,随着应力的增大,体系能带朝远离费米能级方向移动,费米能级附近的电子分布数量减少,电子自旋态密度峰值逐渐下降,体系电子自旋间的交换相互作用程度减弱,轨道电子分布局域性增强,表明铁磁体系的磁性在应力作用下逐渐减弱。通过原子磁矩的计算定量分析了铁磁体系磁记忆信号的变化特征,得到磁记忆信号随着应力的增大逐渐减小,应力与磁信号间存在线性对应关系。当材料发生塑性变形时,磁记忆信号发生突变,信号变化特征发生改变。塑性变形铁磁体系的磁记忆信号随应力变化的斜率小于正常铁磁体系,表明材料在发生塑性变形后力磁耦合程度减弱。设计制作了不含人工缺陷及形状效应的拉伸试样和长距离实验管道,建立了材料拉伸和管道打压实验平台。实验研究了铁磁材料在单向拉伸和三向应力状态下的磁记忆信号特征,得到铁磁材料的应力与磁记忆信号的对应关系。分析了铁磁材料在应力作用下由弹性变形转变为塑性变形时,磁记忆信号的变化特征。实验研究表明,铁磁材料在地磁和应力作用下将产生磁记忆信号,材料表面得磁感应强度随应力的增大而减小,当材料屈服时,磁记忆信号发生突变,塑性变形后铁磁材料力磁耦合程度减弱,磁记忆信号随应力变化的趋势变缓。实验研究结果与理论研究结果具有一致性,验证了理论研究的正确性。以Φ1219输气管道的磁记忆应力内检测为应用背景,对油气管道应力损伤磁记忆内检测技术的工程应用进行研究。提出管道差异运行压力下的二次应力内检测方法,对检测结果进行分析和评价,对检测到的危害点进行现场开挖验证。研究结果表明了油气管道应力损伤磁记忆内检测技术工程应用的可行性和有效性。
[Abstract]:Oil and gas pipeline transportation is an important way of energy transportation because of its high efficiency, low cost, safety and reliability. At present, more than 2.5 million kilometers of oil and gas pipelines have been built all over the world, and this data is still growing every year. The importance of pipeline safety management is determined by the characteristics of high energy, high pressure, inflammable, explosive, toxic and harmful, continuous operation, wide chain and complex environment. The steel materials used in oil and gas pipelines have good mechanical properties such as strength, hardness, plasticity and toughness, and good ferromagnetism. Performance, the occurrence of failure will undergo a process from stress concentration leading to material yield and then plastic deformation to failure. Pipelines in the construction and use process, will be subjected to various stresses, when there are local defects or other quality problems in the pipeline, will produce local stress concentration, resulting in excessive local stress, or even lead to failure. Plastic deformation or failure occurs in pipelines. Stress concentration is an important factor threatening the safety of pipelines. Plastic deformation damage caused by stress concentration is considered as early damage of materials. Magnetic memory testing method as a stress testing method has been recognized by the industry. It has the advantages of simple equipment, easy operation, on-line large-scale non-destructive testing and early judgment of equipment risk. However, there is no unified conclusion on the mechanism and characteristics of magnetic memory signal formation. At the same time, because the weak magnetic memory signal is also affected, the validity of the experimental research method is highly required. Many experimental methods have certain limitations, and can not effectively explain the true situation of magnetic memory phenomenon, which leads to the method in some engineering applications. The magnetism of ferromagnetic materials originates from the magnetic moments of atoms and is determined by the motion and interaction state of the micro-electronic system. Based on the microscopic theory of quantum mechanics and the density functional theory, a theoretical model of magnetic memory effect in ferromagnetic materials with force-magnetic coupling is established. The characteristics of magnetic memory signal during the coupling process are studied. The theoretical results are verified by tensile and compression tests. The engineering application of magnetic memory inner detection technology for pipeline stress damage is carried out. The feasibility and feasibility of the method are verified. In this paper, the mechanical and magnetic properties of ferromagnetic materials are studied, and the micro-mechanism of stress damage and the micro-origin of magnetism are clarified. Based on the micro-electron density distribution function of the system, the quantum mechanical density functional theory model of ferromagnetic materials is established, and the first primitive is used. The energy band structure, electron density distribution and atomic magnetic moment of two ferromagnetic systems, normal ferromagnetic crystal structure and plastic deformed ferromagnetic crystal structure, are calculated by CASTEP. The theoretical results show that the system of ferromagnetic materials under uniaxial and triaxial tensile stress states increases with the increase of stress. The band moves away from the Fermi level, the number of electrons near the Fermi level decreases, the peak value of electron spin density decreases, the exchange interaction between electron spins decreases, and the locality of orbital electrons increases, indicating that the magnetism of the ferromagnetic system gradually weakens under stress. The variation characteristics of magnetic memory signals in ferromagnetic systems are analyzed quantitatively and numerically. It is found that the magnetic memory signals decrease with the increase of stress and there is a linear relationship between stress and magnetic signals. The slope of stress change is smaller than that of normal ferromagnetic system, which indicates that the coupling degree of force and magnetism decreases after plastic deformation. Tensile specimens and long-distance experimental pipes without artificial defects and shape effects are designed and manufactured. The experimental platform of material tension and pipe compression is established. The uniaxial tension and three-dimensional stress of ferromagnetic materials are experimentally studied. The characteristics of magnetic memory signals under stress state are obtained, and the corresponding relationship between stress and magnetic memory signals of ferromagnetic materials is obtained.The characteristics of magnetic memory signals are analyzed when ferromagnetic materials are transformed from elastic deformation to plastic deformation under stress.The experimental results show that ferromagnetic materials will produce magnetic memory signals under the action of geomagnetic and stress. The magnetic induction intensity on the surface decreases with the increase of stress. When the material yields, the magnetic memory signal mutates, the coupling degree of the ferromagnetic material weakens after plastic deformation, and the magnetic memory signal slows down with the change of stress. Based on the application background of magnetic memory stress detection in gas pipeline, the engineering application of magnetic memory stress damage detection technology in oil and gas pipeline is studied. The secondary stress detection method under differential operating pressure of pipeline is put forward, the detection results are analyzed and evaluated, and the dangerous points detected are verified by field excavation. The feasibility and effectiveness of engineering application of stress memory magnetic memory testing technology for oil and gas pipelines are presented.
【学位授予单位】：沈阳工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TE973.6

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