Corrosion Failure Reason of the Heat Exchange Tube of a Acrylonitrile Reaction Gas Cooler

Severe defects such as severe localized corrosion of tubesheets and heat transfer tube bundle ports were found in a reaction gas cooler of an acrylonitrile production unit in a petrochemical company after only a few months of operation. Samples were collected on the spot, and the corrosion morphology and products at the defects were analyzed using optical microscope, scanning electron microscope (SEM), and energy spectrometer (EDS),and the chemical properties of the process media were comprehensively analyzed. Finite element simulation was used to analyze the temperature field of the tube sheet and the heat exchange tube. The results show that the inner wall of the heat transfer tube was severely corroded and thinned at a distance of about 17 to 25 cm from the tube sheet, and the mechanism was H₂SO₄ dew point corrosion. H₂SO₄ originated from sprayed solid particles. The (NH₄)₂SO₄ contained in the interior of the particles decomposed to generate SO₂ in a high-temperature environment (about 440 ℃), which further reacted with residual O₂, H₂O (gas) to generate H₂SO₄.