Failure of Magnesium Anodes in Alkaline Solution

Pitting corrosion has been observed in the internal of a tank after only three years of service in a petrochemical plant. The tank was protected by sacrificial magnesium anodes suspended from the roof. The corrosion occurred as a result of the failure of internal cathodic protection (CP) through the fast consuming and self corrosion of the magnesium anodes.  The analysis of the tank content indicated alkaline electrolyte with pH 9.85 at 60 ⁰C and high conductivity.  The main objective of this paper is to study the magnesium anode corrosion behavior in the same solution of the tank by the polarization behavior of the magnesium anode in the same solution and Simulation of the entire CP system using commercial boundary element analysis software BEASY, and calculate the corrosion rate of the anode. The possibility of using aluminum anodes in the tank solution was also investigated. 

High conductivity of the solution and relatively high temperature accelerate the self dissolution of magnesium anodes. Aluminum anodes are recommended as replacement for the magnesium anodes.