NACE SP0205-2021

Spent sulfuric acid, generated by refinery alkylation units (spent acid), may differ from fresh sulfuric acid (fresh acid) in several ways. The most notable differences between alkylation unit fresh acid and spent acid are the acid concentration, water content, possible contaminants from the alkylation process, temperature of the spent acid entering the tank from the alkylation unit, and the presence of dissolved hydrocarbons and hydrogen. These differences must be taken into consideration when developing inspection strategies, setting inspection intervals, performing an external inspection, and internally inspecting a tank that is in spent sulfuric acid service. This standard was developed to address these differences, as they may have an impact on the integrity of spent sulfuric acid storage tanks.