Internal corrosion threats of equipment are primarily due to the presence of carbon dioxide (CO2-sweet corrosion) and/or hydrogen sulfide (H2S-sour corrosion). At low temperatures, below ~150ºC, the corrosion reactions require the presence of water to form an electrolyte (dry gases are non- corrosive).

At the higher temperatures, as found in refinery processing and the flame side of boilers, the corrosion reactions involve gas phase reactions, molten salts and diffusion of metallic and sulfur/oxygen ionic species through the corrosion product scales (oxidation processes).