Two case histories in which high pressure natural gas coolers had failed due to the presence of carbon dioxide are reviewed. CO2 along with CO and H2S are acid gases usually present in natural gas feeds. Carbonic acid can form in aqueous condensate, lowering the pH and locally corroding mild steel tube metal. Stress corrosion cracking (SCC) can occur in tubing containing residual tensile stresses from welding or
manufacturing. Bicarbonates and carbonates concentrated in condensate from CO2 and CO present in natural gas are required to produce SCC. Cathodic depolarizers such as oxygen in conjunction with the presence of carbonic acid will increase the corrosion rate of mild steel. Oxygen also increases the susceptibility of mild steel to carbonate SCC. Keywords: natural gas cooler, carbonic acid, condensate, stress corrosion cracking, residual stress, chemical treatment, zero charge potential, steady state potential