EXTERNAL CORROSION CONTROL OF THE UNDERGROUND STEEL PIPELINES USING CATHODIC PROTECTION SYSTEMS

Abstract

The thesis discusses the cathodic protection technique used for corrosion mitigation of underground steel piping. Since corrosion and cathodic protection are electrochemical processes involving electrical current and an exchange of charged ions, electrical models can be developed. The main objective of the thesis is study of the cathodic protection systems of underground steel piping to develop equivalent electrical models, which can be used in simulation of such systems. These equivalent models can be prepared through the electrical modeling for the electrode/electrolyte interface by Randle’s circuit model. The study herein is based on that the activation (charge-transfer) polarization appears only at the electrode; i.e. in the absence of concentration (mass-transfer) effects, thereby Randle’s circuit model is composed of a double-layer capacitance (Cdl) in parallel with the polarization resistance (Rp). The equivalent models can enable us to validate the design procedures of cathodic protection systems by the knowledge of the polarization amount which can occur for the pipeline potential as a result of applying the cathodic protection. Also through these models, the impact of pipeline polarization resistance on applying the cathodic protection can be simulated. Simulation and results examining are performed by using MATLAB/SIMULINK program and the study assumes that the soil along the pipeline is homogenous.