The aim of this work is to investigate the level of damage to the heat exchanger in a Sulfur Recovery Unit (SRU) of a petroleum refinery. The by-products of oil refining are submitted to special treatment in order to meet technical specifications of corrosivity, sulfur content, acidity, formation of pollutant compounds, and color alteration. Sulfur is removed from the by-products in the form of H2S, which is an acid gas that is sent to the SRU for sulfur production. The gases in the SRU are H2S, CO2, SO2, and SO3, which are corrosive to the mild steel equipment. The Unit is frequently forced to paralyze its activities due to the corrosion of its heat exchangers and pressure vessels, and the acid gas load is burnt causing the release of SOx into the atmosphere. The above occurs when generalized corrosion damages SRU equipment. The importance of this work is to emphasize that the leakage of acid gas and sulfur into the atmosphere is a direct result of corrosion, which causes economical and environmental damage. This study may be used to improve the control of The Claus Process and to minimize corrosion damage. The SRU does not, at present, carry out any corrosion prevention methods. The corrosion of mild steel is controlled by correct air admission to oxide H2S, and to produce SO2, which is the reagent in the reaction of sulfur production. (C) 2006 Elsevier Ltd. All rights reserved.