Underdeposit Corrosion in Crude Tower Overheads

摘要

Ammonium chloride (NH4CI) corrosion is an aggressive form of localized, underdeposit corrosion commonly found in overhead equipment and piping associated with crude units. This happens when ammonia (NH3) and hydrochloric acid (HCI) in the vapor react to form NH4CI salt. Being hygroscopic, NH4CI absorbs moisture, leading to severe localized attack. Given the unpredictable nature of this damage mechanism, appropriate operational, materials, and chemical controls should to be set in place. This article summarizes case studies where this form of corrosion was observed, along with mitigation strategies.