Design and analysis of the cathodic protection system of oil and gas pipelines, using distributed equivalent circuit model

Abstract

Cathodic protection (CP) method is widely used in the oil and gas industry in order to prevent (or reduce) rust and corrosion of structures and metal pipelines or their associated cost. To guarantee a more effective CP system, an applicable design for the under protected structures is required. The conventional models recommended by the designers are based on the equivalent circuit of the overall CP system, which are lumped model and may be useful for the compact systems like integrated industrial plants, where oil and gas pipelines are installed in kilometers. Since such a lumped model leads to inaccurate results, this study aims at proposing a new distributed model to design a cathodic protection system for oil and gas transmission pipelines, which is extendable and can be useable in other structures. The main difference between the proposed model and the conventional approach is the use of actual measured soil resistance throughout the structure instead of using a fixed mean value. The effectiveness of the proposed model has been demonstrated by analytical analysis and computer-based simulations. The proposed method shows a significant superiority over the conventional lumped models when variation of the soil resistance through the structure is high. Hence, the application of the devised method in design of a CP system of the pipelines improves the quality of the protection. The distributed equivalent circuit model with its distributed parameters is utilized to design and analyze the performance of a real case i.e., the CP protection system of a 20-km transmission pipeline with soil-measured data. To calculate the performance of the designed CP system, the results are compared with those of the conventional model.