Study On Cathodic Protection Potential Distribution Of Bottom Slab Of Storage Tank In North Station

Once the storage tank bottom corrosion perforation occurs, bringing huge economic losses, affecting the whole station normal production order, causing serious pollution to the environment. This paper takes Yaha loading south station1#tank bottom cathodic protection system as the research object. Based on the storage tank operational status, the actual tank bottom corrosion mechanism is studied. There are risks of corrosion perforation for tank floor.1#tank bottom plate is verified using impressed current cathodic protection to prevent corrosion from occurring on external tank bottom is needed. At the same time, in the process of the tank bottom cathodic protection system effectiveness testing finds that1#tank long-term reference electrode placed around the tank bottom. It is difficult to measure the center of the tank bottom cathodic protection potential. The protective effect of the center tank bottom is difficult to predict, increasing the risk of the tank bottom corrosion perforation. Therefore, the establishment of mathematical model of cathodic protection potential distribution on tank bottom, and using numerical simulation to calculate the potential distribution of tank bottom, having great significance in improving the effectiveness of cathodic protection and ensuring the safety of the tank bottom.Based on the characteristics of the storage tank structure of deep well anode impressed current cathodic protection system, three-dimensional semi-infinite domain physical model is established. Deep well anode is simplified as pointes source column shape set. From the theory of constant current, Poisson equation is derived as the potential distribution control equation. According to actual situation, the polarization properties of metal tank bottom is considered, the boundary conditions are studied, and the mathematical model of cathodic protection potential distribution on the exterior of tank bottom is established. Comparing the advantages and disadvantages of finite difference method(FDM), finite element method(FEM) and boundary element method(BEM), BEM is chosen as a method for solving the mathematical model.According to the principle of BEM, the fundamental solution of three dimensional semi-infinite domain model is derived. Using isoparametric quadrilateral element to discrete tank bottom boundary. Mathematical model of the potential field becomes algebraic equation, and cathodic protection potential distribution question becomes mathematical problems of solving algebraic equations. Influence coefficient of source point units and non-source point units is calculated with gauss integral method and degradation element method. In order to solve the model, piecewise linear match is induced to fit cathodic polarization curve. Establishing tank bottom cathodic protection potential distribution simulation program based on BEM, and comparing COMSOL calculation results, the calculation results are in good agreement. So this paper establishes mathematical model and calculation method can be used to predict the cathodic protection effect of tank bottom. Calculation results show that1#tank across the bottom of the lateral potential values are within the scope of protection, the size of the potential between-0.971V and-1.115V. The most positive potential is on the center of the tank bottom. The potential of the edge of the tank bottom is more negative than the potential of the center of the tank bottom. The potential of the point near the anode is more negative than the potential of the point far from the anode.On the basis of calculation of potential distribution on tank bottom under cathodic protection by using BEM, the influence of the difference of setting parameters of anode and soil resistivity on tank bottom cathodic protection potential distribution are studied. Studies show that with the increase of deep well anode buried depth, length of anode well or the distance away from the storage tank, tank bottom potential shift in the positive direction. With deep well anode output current increases and the number of deep well anode increases, tank bottom potential shift in the negative direction, the current size should be maintained at between6A and8A. A single tank is generally set1-2deep well anodes in practical engineering applications is appropriate. Soil resistivity increases, tank bottom potential shift to positive direction. Current size and soil resistivity are the most main factors that influence the potential distribution.