<p>This paper presents a comprehensive failure analysis performed on a shell nozzle of an ammonia rectifier tower heat exchanger belonging to the sour water treatment unit of an oil refinery, which failed in operation. The study investigates the main causes of the failure using ultrasonic thickness measurement techniques, visual inspection, chemical composition, microstructure analysis, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and optical profilometry analysis. Potentiodynamic polarization electrochemical corrosion tests were also performed to select materials that are more resistant to the operating environment. The results indicated that HS⁻ ions react with the iron in carbon steel, promoting metal oxidation and forming corrosion products such as insoluble iron sulfides that deposit on the surface, causing corrosion in the equipment nozzle. This ammonium disulfide corrosion process was the main cause of equipment failure, and as a countermeasure, the nozzle was replaced at this time.</p>