牙哈装车南站储罐底板阴极保护电位分布研究

发布时间：2018-05-20 04:28

本文选题：储罐底板 + 阴极保护　；参考：《西南石油大学》2015年硕士论文

【摘要】：储罐底板一旦发生腐蚀穿孔,会带来巨大的经济损失,影响整个站场正常的生产秩序,还会对环境造成严重的污染。本文以牙哈装车南站1#储罐底板为研究对象,从储罐运行现状出发,对储罐底板发生腐蚀的机理进行了研究,分析得到储罐底板有腐蚀穿孔的风险,验证了1#储罐底板采用外加强制电流阴极保护防止罐底板外侧发生腐蚀的必要性。同时在储罐底板阴极保护系统有效性检测过程中发现1#储罐的长效参比电极安置在罐底板周围,罐底板中心的保护电位难以通过测量获得,罐底板中心保护效果的预知性差,增加了罐底板腐蚀穿孔的风险。因此建立储罐底板阴极保护的电位分布数学模型,运用数值计算方法模拟计算储罐底板的电位分布,对于提高阴极保护效果,确保储罐底板的安全具有非常重要的意义。针对储罐底板深井阳极强制电流阴极保护系统构成的特点,建立了三维半无限域物理模型,深井阳极简化为列状集中点源。基于恒电流理论,推导得到Poisson方程为电位分布的控制方程。根据实际情况,考虑罐底板金属的极化特性,对边界条件进行研究,最终建立了储罐底板阴极保护电位分布数学模型。分析比较有限差分法、有限元法和边界元法三种方法的优点和缺点,选取边界元法作为该数学模型的求解方法。根据边界元法的求解原理,推导得到了三维半无限域模型的基本解,采用等参四边形单元对罐底边界进行离散,电位场的数学模型经过边界离散后化为代数方程,阴极保护电位分布问题变为求解代数方程组的数学问题。采用高斯积分法与退化单元法计算不含源点单元影响系数和含源点单元影响系数。为了求解模型,采用分段拟线性化法对阴极极化曲线进行了处理。编制了基于边界元法的储罐底板阴极保护电位分布仿真程序,并采用COMSOL软件模拟验证计算结果,模拟结果与储罐底板阴极保护电位分布程序计算结果基本吻合,验证本文建立的数学模型及计算方法可以用来预测储罐底板的阴极保护效果。计算结果表明,1#储罐整个底板外侧的电位值都在保护范围之内,电位大小在-0.971V～-1.115V之间,电位最正值在罐底板中心附近。罐底板边缘的电位负于罐中心的电位,且近阳极点的电位负于远阳极点的电位。在运用边界元法计算储罐底板阴极保护电位分布的基础上,分别研究了包括阳极设置参数、土壤电阻率等因素对储罐底板阴极保护电位分布的影响。研究发现：随着深井阳极埋深增加,阳极井长度增长,或是增加深井阳极距储罐的距离,储罐底板电位向正方向偏移；随着深井阳极输出电流增大,阳极井数量增多,储罐底板电位向负方向偏移,电流大小应保持在6A～8A之间,实际工程应用中单个储罐一般设置1～2口阳极井为宜；土壤电阻率增大,储罐底板电位均向正方向偏移,电流大小和土壤电阻率影响电位分布最为显著。
[Abstract]:Once the tank floor is corroded and perforated, it will bring huge economic loss, affect the normal production order of the whole station and cause serious pollution to the environment. This paper takes the 1# storage tank floor of the South Station of yazakhstan loading car as the research object. From the running status of the tank, the mechanism of the corrosion of the tank floor is studied, and the storage is analyzed and stored. The tank floor has the risk of corrosion and perforation, which proves the necessity of preventing the corrosion of the bottom plate of the tank floor by the forced current cathodic protection of the 1# storage tank. At the same time, it is found that the long effect reference electrode of the 1# storage tank is placed around the bottom plate of the tank in the process of the effectiveness detection of the cathodic protection system of the tank floor. The protection potential of the tank bottom center is difficult. Through the measurement, the prediction of the center protection effect of the tank bottom is poor, which increases the risk of corrosion perforation of the tank floor. Therefore, a mathematical model of potential distribution for the cathodic protection of the tank floor is established, and the potential distribution of the tank floor is simulated and calculated by the numerical calculation method, so as to improve the protection effect of the negative pole and ensure the safety of the tank floor. It is often important.
In view of the characteristics of the Fukai Yogoku forced current cathodic protection system of the tank floor, a three-dimensional semi infinite field physical model is established. The deep well anode is simplified as the column central point source. Based on the constant current theory, the control equation of the Poisson equation as the potential distribution is derived. According to the actual situation, the polarization characteristics of the metal in the tank floor are considered, and the boundary is considered. The conditions are studied, and the mathematical model of the cathodic protection potential distribution in the tank floor is established, and the advantages and disadvantages of the three methods, finite difference method, finite element method and boundary element method are analyzed and compared, and the boundary element method is selected as the solution of the mathematical model.
According to the principle of solving the boundary element method, the basic solution of the three-dimensional semi infinite domain model is derived. The isoparametric quadrilateral element is used to discrete the boundary of the bottom of the tank. The mathematical model of the potential field is transformed into an algebraic equation after the boundary is discrete. The problem of the distribution of the cathodic protection potential becomes the mathematical problem of solving the algebraic equations. The Gauss integral method is used. In order to solve the model, a piecewise quasi linearization method is used to deal with the cathodic polarization curve. A simulation program for potential distribution of cathodic protection in tank floor based on boundary element method is developed, and the simulation results are simulated and verified by COMSOL software. The results are in good agreement with the calculation results of the cathodic protection potential distribution program of the tank floor. The mathematical model and calculation method established in this paper can be used to predict the cathodic protection effect of the tank floor. The calculation results show that the potential value of the whole floor of the 1# tank is within the range of protection, and the potential is between -0.971V and -1.115V. The potential is most near the center of the tank floor. The potential at the edge of the tank plate is negatively related to the potential of the tank center, and the potential near the anode is negative to the potential of the far Yang pole.
On the basis of using the boundary element method to calculate the cathodic protection potential distribution of the tank floor, the influence of the parameters of the anode setting and the soil resistivity on the cathodic protection potential distribution of the tank floor is studied. The study shows that the length of the anode well grows with the depth of the deep well anode increase, or the distance of the deep well anode tank. The potential of the tank bottom is shifted to positive direction; with the increase of the output current of the deep well anode, the number of anode wells increases, the potential of the tank bottom is shifted to negative direction, and the current size should be kept between 6A and 8A. In actual engineering applications, 1~2 anode wells are generally set in a single storage tank; the soil resistivity increases and the potential of the tank floor is to the square. The distribution of potential is most significant to offset, current size and soil resistivity.
【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】：TE972

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