Optimization of Wire Anode Distance from Pipe in Impressed Current Cathodic Protection System

Installing wire anode alongside of a pipe is a common arrangement for impressed current cathodic protection system in complex plant, localized protection and congested areas. The installation cost and difficulties arise by increasing distance of anode as well as uncontrolled closing anode could cause overprotection in the nearest side of the pipe to anode while other part may not in the protection range. Hence optimizing wire anode-pipe distance is a general approach in this technology. For the first time, analytical equation is extracted for the common boundary conditions with general parameters included soil resistivity, pipe diameter and maximum allowable potential difference of the pipe surface. Based on the generated equation by considering 0.35 V maximum potential variation on the pipe, which is a potential difference between protected side with -0.850 V vs. Cu/CuSO4 (CSE) and overprotection limit -1.2 V vs. CSE, in low resistive environment, 20-30 cm distance anode-pipe could produce even potential distribution for common size of pipes. In the same situation but moderate and high soil resistivity, the minimum distance is higher than mentioned value and also common available space in pipe trench. In these cases the minimum distance should be checked based on the extracted equation and obtained graphs or the number of anodes should be increased for reaching to the acceptable asymmetry in potential gradient. Moreover reducing the potential gradient gap will increase the effect of pipe diameter beside soil resistivity. The results approve by mathematical simulation of the system for the selected situations. FEM analysis by considering Butler-Volmer boundary condition for the cathode shows the nonlinearity of the polarized potential and possible hidden under- and over-protection area in wire anode-pipe common arrangement.