Scheme Research On The Regional Cathodic Protection Of The Oil Tank Farm

As a kind of station,the corrosion of oil tank farms,especially the corrosion of tank bottom is becoming more and more serious since the difficulty of regional cathodic protection is increased due to the complex protection object,the serious interference shielding and the huge grounding system.Therefore,the establishment of oil tank farm regional cathodic protection potential distribution model for studying on the potential distribution of tank bottom and pipeline plays an important role in oil tank farm to improve the effect of cathodic protection.Based on the actual situation of tank farm and environment,a physical model for the three-dimensional and semi-infinite regional cathodic protection system is established by reasonable assumption and simplification.And according to the same principle of constant electric field and electrostatic field,the governing equation of cathodic protection potential distribution is derived.The polarization characteristics of bottom plate and pipe are measured in laboratory experiments,and the piecewise linear fitting method is used to deal with polarization curves.Finally,the regional cathodic protection potential distribution mathematical model of the oil tank farm is established.Several common numerical algorithms are compared,and the three-dimensional boundary element method is used to solve the model considering the actual situation of the problem and ensuring the accuracy of the calculation results.The basic solution of the mathematical model for three dimensional semi-infinite domain is derived by using the mirror method and electric field superposition principle,and the isoperimetric linear quadrilateral element and the pipe element are used to separately the bottom plate and pipe as well as the auxiliary anode is treated as a point source,which make the mathematical model changed as an algebraic equation.The non-singular coefficient matrix and the singular coefficient matrix are calculated by using the Gauss integral method and the degenerate element method respectively.The solver program for the regional cathodic protection potential distribution of the oil tank farm is designed,and using this program the simulation calculation of the bottom plate potential of an actual storage tank is carried out.The results of the calculation are in good agreement with the measured results,which verifies the accuracy and reliability of the program.The indoor simulation experiment device for regional cathodic protection is established,which can achieve the measurement of the protective potential on the tank bottom and the pipeline.By using the method of self-made needle type bridge,the effect of soil resistance drop is avoided in the process of potential measurement.And a series of laboratory experiments are conducted to determine the soil resistivity.The effects of various factors,that include the anode parameters,such as anode well distance,depth and quantity,and soil resistivity,on the potential distribution of single tank bottom plate and multi tank bottom plate are studied by comparing the results of laboratory experiments and the simulation results,and the variation law of various factors on the potential is obtained,which provides theoretical support for the improvement of regional cathodic protection design and tank.