The Establishment And Application Of Mathematical Model In Cathodic Protection Of Submarine Pipeline With Damaged Coating

With the rapid growth of marine economy, the sea industrial activities are becoming more and more frequent, today is the day of rapid development of global economic integration, the demand for marine energy of the world continues to expand. It makes the development of offshore oil and gas resources climax. With the rapid development and production of offshore oil and gas field development. As the link between production and transportation of the offshore oil and gas, submarine pipeline plays an important role. The submarine pipelines are always in a harsh marine environment, it seriously affects the service life and the safety of submarine pipeline. Because most of the pipelines are buried in the seabed sediment environment, it brings difficulties to the detection maintenance and repair of pipelines. Through the cathodic protection potential distribution of pipelines running under the sea, we can master the damage of coating, discover the corrosion tendency, in order to take measures to repair, eliminate the hidden trouble of safety and extend the service life of the tube.At present, the numerical simulation has been widely used in the field of cathodic protection. The mathematical model has been succeed to calculate the potential distribution of cathodic protection and become an important means for the optimization design of cathodic protection. It has been well actualized in the cathodic protection of offshore platform and land oil (gas) pipelines. But in the cathodic protection of submarine oil and gas pipelines, especially for the cathodic protection potential distribution of underwater submarine pipelines with damaged coating, the mathematical model and numerical calculation method are needed to be further studied. Therefore, it is necessary to do research on the cathodic protection of submarine pipelines with damaged coating and establish a mathematical model which is applicable to the cathodic protection of submarine pipelines damaged coating. To get the potential distribution of cathodic protection by the correct calculation. It is very important for master the coating damage of the real operation, discover the corrosion tendency in order to take measures to repair, eliminate safety hazards and extend the service life of the tube.In this paper, according to the breakage of coating in real operation of submarine pipelines, based on the similarity theory and dimensional analysis theory, use the (?)273mmx 12000 mm actual submarine pipeline, install an Al-Zn-In-Si bracelet sacrificial anode to form a cathodic protection system, design the experimental device of cathodic protection of submarine pipeline under water. A large scale simulation experiment is carried out. To get the potential distribution of cathodic protection and the polarization parameters of the cathodic protection system. In order to obtain the required boundary conditions of the mathematical model for numerical calculation. The potential distribution data can be used to verify the rationality and correctness of the mathematical model. The boundary conditions can further provide basic conditions for the calculation of pipeline coatings with different degree damage, and provide data support for the subsequent establishment of mathematical model database.Based on the combination of Laplace equation and the boundary conditions, establish the mathematical model of the cathodic protection of the submarine pipelines with damaged coating. Take different values for the apparent resistivity of boundary conditions and use the finite element method. When the apparent resistivity of coating is equal to 2000 kΩ·cm2, The FEM calculation results are reasonable. The potential distribution of the actual experimental measurement and numerical calculation are in good agreement. To prove the correctness of the mathematical model. It can be used to evaluate the effect of cathodic protection. Based on the analysis of the anode, the cathode, the apparent resistivity and the FEM, to solve the error generated by calculating.The actual experimental measurements and numerical results are in good agreement, it can fully explain the correctness of the mathematical model. According to the parameters of the actual sea pipe and boundary conditions, through the finite element calculation to get the potential distribution of the coating different damage rate, different damage shape and compare the calculation results. To get the effect of cathodic protection and potential distribution in different boundary conditions. Provide the data base for the further database of mathematical model in cathodic protection of submarine pipeline with damaged coating.