Analysis on the under deposit corrosion of air cooler tubes: Thermodynamic, numerical and experimental study

Failures of air cooler tubes caused by under deposit corrosion of NH4Cl salts are investigated in this paper. The corrosion mechanism is determined by the analysis on the micro-morphology and chemical composition of corrosion products. Thermodynamics calculation indicates that the corrosion region inside the air cooler tubes is closely correlated to the crystallization temperature of NH4Cl salts and the dew point temperature of water. The numerical simulation demonstrates that the NH4Cl salts tend to deposit on the upper surface of tubes. The maximum concentration of NH4Cl salts locates at 0.65 m-0.73 m away from the tube entrance when the multiphase flow velocity ranges from 3.5 m/s to 5.0 m/s. In the experiments of under deposition corrosion, the similar micro-morphology as the actual localized corrosion is found in the specimens of carbon steel. The anti-corrosion performance of 316 L stainless steel is much better than carbon steel at different temperatures and humidity, which explains why the corrosion of tube liners is not serious as the tube bundles.