Computer Program And Numerical Experiment On Boundary Element Method Of Cathodic Protection Based On Pipe Element

Numerical simulation can accurately predict the effect of cathodic protection design, so numerical simulation has been extensively applied in field of corrosion and protection because it makes up for the deficiency of traditional cathodic protection. The regularity of potential distribution was calculated based on the boundary element method(BEM) and its extended work was researched.Potential distribution accords with Laplace differential equation in steady corrosive field based on Gauss divergence theorem and Green formula. Boundary integral equation was derivated by means of weighted residual method and fundamental solution of governing equation as trial function. Boundary integral equation was dispersed to obtain system of linear equations containing unknown potential and current density values using pipe element. Besides, this thesis discussed the advantage of less unknown values and workload and avoiding dealing with boundary non-continus points and singular integral of pipe element method. The application program of SKLBEM was written by C#to caculate the potential and current density distribution with piecewise linear fitting treating nonlinear boundary condition. The caculated result of SKLBEM meets the result of finite element software of ANSYS and experimental measurement.Potential distribution of cathodic protection is influenced by resistivity of electrolyte, size of protected device, type and arrange of anode and option of boundary condition. The influence of pipe diameter, electrical resistivity, distance between anodes and polarization curve on potential distribution was discussed in this research. With pipe diameter increasing, the protection distance largened and the calculated protection radius accords with classical cathodic protection theoretical formula. The regularity of potential distribution of electrical resistivity stated potential shifted to the negative direction in case of low electrical resistivity. The caculated potential value with polarization curve of high polarization resistance rate was more negative.The max scan rate was confirmed according to its influnce on polarization curve by analysing alternating-current impedance of electrodes in practical system. The max scan rate of correct polarization curve was proportional to relative error of polarization current and scan range of voltage and inversely proportional to resistance and capacitance of reaction. The scan rate reduced proportionately with resistance and capacitance increasing. The reaction impedance of Q235steel firstly increased.then reached the maximum at a certain potential and reduced at last with protective potential moving negatively. When reaction impedance reached to the max value, the potential was optimum protection potential changed due to surface states of electrode and moved positively when calcium and magnesium salt deposited.