Effect of Corrosion on Steel Storage Oil Tanks

Abstract

Corrosion is one among many degradation mechanisms of steel aboveground oil storage tank structures. Therefore, for tanks in long-term service, a major issue becomes loss of thickness close to, or below, minimum acceptable values, there are many standard and empirical approaches to evaluate the fitness for service of corroded tanks. This study conducted to determine the probabilistic integrity and fitness for service of a bottom plate of an above-ground steel tank by considering the serviceability of the tank as a function of critical thickness profile. The results show that when the coefficient of variation of the measured thickness fall below 10% the fluctuation in thickness through all surface area of the bottom can represent by an averaged value considered the critical thickness. Finite element analysis is conducted to verify the results and, to specify the spots of stress concentration. The remedial action taken is to strengthen the structure by weldment of an annular plates and partial replacement of the plates with minimal thickness. Adopting this procedure result a repair cost saving of 52%, minimizing the downtime to 44.4%, and the rate of return reduced to 49.2%, furthermore a new layout and design basics were made for future construction.