钢板电化学腐蚀声发射机理研究

发布时间：2018-03-19 00:18

本文选题：声发射信号　切入点：有限元仿真　出处：《沈阳工业大学》2015年硕士论文　论文类型：学位论文

【摘要】：石油储罐的建设促进了我国经济的快速发展，但同时也带来潜在的危险，储存介质具有高温、高压、高腐蚀性等特征，特别罐底容易发生因腐蚀而引起的破裂等损伤。声发射检测技术作为一种新型的无损检测方法已经广泛应用于储罐罐底腐蚀检测中。本文主要从罐底腐蚀机理，腐蚀产生的声发射信号特征，如何根据腐蚀产生的声发射信号判断腐蚀进程等几个方面进行研究。本文介绍了声发射信号的产生原理和罐底腐蚀机理。由于罐底长期承受来自油品和自身重量的压力，同时由于底板和地基等变化而变形，造成罐底与雨水、露水或其他电解质直接接触发生电化学腐蚀。针对储罐材料、所处环境及常见腐蚀类型，在此着重研究了钢板的电偶腐蚀声发射机理。综合分析电偶腐蚀机理和腐蚀产生声发射信号的原理，结合电化学腐蚀动力学理论，借助COMSOL有限元仿真软件建立二维有限元模型。模拟了钢板局部腐蚀缺陷的扩展路径和能量分布，直观地描述了在腐蚀过程中交换电流密度，电偶腐蚀速度和电极电势。由于影响电偶腐蚀的因素较复杂，本文针对比较重要的因素，即电偶腐蚀中电极材料的阴、阳极面积比进行仿真研究。结果表明，电极电流在偶接处最大，所以金属的溶解程度在该点最大；阳极交换电流的峰值位于偶接处，由于电极表面存在压降，因此远离偶接处的阳极交换电流密度逐渐减小。随着加载时间的推移，电偶腐蚀电极的各点处的交换电流密度并没有明显的变化；在相同条件下，阴极面积越大造成的电偶腐蚀现象越明显，即单位时间内电偶腐蚀速率越大，但是二者并不成线性关系。分析得到的不同的仿真结果，对比腐蚀原理验证建立的仿真模型的正确性，为实验提供理论依据。根据课题需要使用PIC-2声发射检测系统对钢板分别在空气中，10%氯化钠溶液中以及钢板-铝板在10%氯化钠溶液中发生电偶腐蚀行为进行长时间连续实时检测。结果表明，单位时间内腐蚀越严重的钢板，产生的声发射事件个数越多。通过腐蚀模拟实验数据与电偶腐蚀仿真结果相比，单位时间内检测到声发射事件个数可以对电偶腐蚀速率进行定性的判断，，进一步可根据量值变化推断腐蚀趋势。
[Abstract]:The construction of oil storage tanks has promoted the rapid economic development of our country, but at the same time, it also brings potential dangers. The storage medium has the characteristics of high temperature, high pressure, high corrosion and so on. As a new nondestructive testing method, acoustic emission (AE) detection technology has been widely used in tank bottom corrosion detection. In this paper, the corrosion mechanism of tank bottom is discussed. The characteristics of acoustic emission signals produced by corrosion and how to judge the corrosion process according to the acoustic emission signals produced by corrosion are studied. This paper introduces the generation principle of acoustic emission signal and the corrosion mechanism of tank bottom. The tank bottom and Rain Water are deformed because the bottom of the tank bears the pressure from oil and its own weight for a long time, at the same time, because of the change of bottom plate and foundation, etc. Electrochemical corrosion occurs in direct contact with dew water or other electrolytes. The acoustic emission mechanism of galvanic corrosion of steel plates is mainly studied in view of the environment and common corrosion types of tank materials. The mechanism of galvanic corrosion and the principle of acoustic emission signal generated by corrosion are analyzed synthetically, and combined with the theory of electrochemical corrosion kinetics, The two-dimensional finite element model is established by using the COMSOL finite element simulation software. The propagation path and energy distribution of the local corrosion defects of steel plate are simulated, and the exchange current density during the corrosion process is described intuitively. Due to the complexity of the factors affecting the galvanic corrosion, the anodic area ratio of the electrode material in the galvanic corrosion process is studied by simulation in this paper. The electrode current is the largest at the junction, so the dissolution degree of the metal is the largest at this point, and the peak value of the anode exchange current lies at the junction, because of the voltage drop on the electrode surface. As a result, the exchange current density of the anode away from the coupling site gradually decreases. With the loading time, the exchange current density at each point of the galvanic corrosion electrode does not change significantly; under the same conditions, The larger the cathode area, the more obvious the galvanic corrosion, that is, the larger the galvanic corrosion rate per unit time, but not the linear relationship between the two. Compare the corrosion principle to verify the correctness of the established simulation model, and provide a theoretical basis for the experiment. The galvanic corrosion behavior of steel plate in 10% NaCl solution in air and the galvanic corrosion behavior of steel plate and aluminum plate in 10% sodium chloride solution were detected by PIC-2 acoustic emission detection system for a long time. The results show that, The more seriously corroded the steel plate per unit time, the more acoustic emission events are generated. Compared with the simulation results of galvanic corrosion, the corrosion simulation data are compared with the results of galvanic corrosion simulation. The number of acoustic emission events per unit time can be used to judge the galvanic corrosion rate qualitatively, and the corrosion trend can be further inferred according to the quantity variation.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE988

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