Latest advances in the understanding of acid dewpoint corrosion: corrosion and stress corrosion cracking in combustion gas condensates

Corrosion failures due to condensing flue gases containing H₂O, SO₃, NO_x and HCl still occur more often than might be expected. The corrosion failures can be of several types: general corrosion, pitting attack and stress corrosion cracking (SCC). The chemistry of condensing gases is discussed, and some examples of corrosion in large‐scale installations are presented, including blast stoves for steel production, heat recovery steam generators, and waste incineration boilers. The use of thermal insulation inside boiler casings can result in nitrate SCC when the flue gas contains high concentrations of NO_x. Nitric acid from flue gas can react with carbon steel and insulation material forming ammonium nitrate and calcium nitrate. Both materials have hygroscopic properties and are very corrosive, even above the water dewpoint of the gases.