The Study Of Cathodic Protection Potential Distribution Modeling Of Titanium Tube Condenser In Coastal Power Plant

In our country, seawater is used to be cooling water in coastal power plants. Because seawater is high corrosive environment, there is a fierce trend of galvanic corrosion in the condenser which is constituted of two kinds of metal, for example carbon steel room and titanium tube. The sacrificial anode cathodic protection (SACP) is main corrosion prevention technique in condenser of power plants. It must be make sure that the potential of joint of steel-room and titanium-tube is at -0.80V during protection course; If the potential is positive more than it, the steel will be under protection and if it is negative more than it, titanium tube will be hydrogen embrittlement. At the same time, for the complex structure of condenser and electro-shield, it will cause steel under-protection and titanium overprotection in the process of protection, too. Therefore, the potential of the metal surface in condenser must be controlled in a certain scale to make condenser under valid protection. In order to design appropriate SACP system, acknowledge of the electrochemical potential across condenser surface is necessary. At the same time, it is the important accordance of the optimization SACP design and evaluation of SACP protection quality.In decade, further comprehension of the theory of CP and the maturing of computer technology enable corrosion engineers to obtain numerical methods for the modeling of CP.This paper inquires into the usage of the finite element method (FEM) in distribution of electrochemical field of power plants condenser water-box model under SACP. Ascertaining boundary conditions is the most critical part of mathematical model, that is, the relationship between the potential and the current density and how this relation changes with time. It will be necessary to obtainboundary conditions that are compatible with the actual state of the structure. In the model cathodic polarization of both specimen and galvanically coupled carbon steel and titanium are studied. To attain boundary condition, main works as follows: 1 .Water-box model is designed according to the structure of actual power plant. The area ratio of carbon steel (Q235B) and titanium (TA2) is 55 to 1.2. In the water-box model, SACP system is designed, moreover one anode or two anodes are used respectively.3. Because the size of model is too small to simulation actual condenser cathodic protection. Seawater and diluted seawater are used as experiment media.4. The boundary condition experiments used for numerical calculation are performed. According to cathodic polarization characterization of two kinds of metal in seawater and diluted seawater, different electrochemical methods are used. First, potentiostatic polarization, polarization by changing polarization potential in different time interval and dynamic potential slow scan polarization are designed in two experiment media for specimen. Dynamic weak polarization techniques, EIS, galvanostatic charge technique, slow scan cyclic voltammetry (CV) curve are introduced. To Q235, invariable current density polarization experiments are designed. Scanning electron microscopy (SEM) is used to observe the surface of Q235B under different time intervals changing polarization potential polarization in seawater.5. The potential distribution and protection current of cathodic protection in water-box model are determined. Meanwhile the electrochemical dynamic parameters of carbon steel in actual sacrificial anode cathodic protection are measured by EIS.Mathematical model of potential distribution of water-box is investigated in this paper. According to the polarization energy balance principle, cathodic protection field mathematical model is set up by the boundary conditions. To solve LAPLACE equation, tetrahedron unit and appropriate function are applied to discrete structure, surface and its environment. Through analysis of each unit and synthesis in the whole area, mathematical model of 3-D for water-box model is constructed.The result which was calculated by FEM is consistent well with the data which were got from the experiments, that is, FEM can calculate and solve cathodicprotection potential distribution of complex structure such as carbon steel room and titanium tube condenser. The physical model and mathematical model the paper brings forward are available.