Design Life and Site Survey Data Analysis of Aluminum Alloy Anode for Cathodic Protection
Katsuya MAYUMI and Nobuhiko TAKAGi
Abstract:On the cathodic protection for marine steel structures, total weight demand of aluminum alloy anode is remarkably influenced by the life of anode set up at site, therefore an accurate expected anode life is indispensable factor for the cathodic protection design. The analysis of the site survey data that had been executed in the past was tried to verify the relation to which the potential and the current density decayed according to time in the cathodic protection of steel in seawater. By this analysis, in the protective current density condition below the dissolved oxygen diffusion limiting current density of the examination sea area, it is confirmed that the relationship (slope parameter) of potential vs. current density is certainly linear with the corresponding to the anode potential. In view of a linear relation between the potential and the current, the anode life can be evaluated by the cathode potential because the anode generation current is decided certainly by not the ohmic resistance calculated from anode shape but the cathode potential. That is, it is necessary to review the method of calculating the anode life because the anode generation current is in the relation controlled automatically by not the ohmic resistance of the protection circuit but the cathode potential. This paper describes the outline of the anode design based on slope parameter obtained by the site survey data analysis. Key Words:Marine steel structures, Aluminum alloy anode, Relationship of potential（φ）and current density（ｉ）decay, Slope parameter, Dissolved oxygen diffusion limiting current density