Abstract: During the operation of a 1.5 million tons/year residue hydrotreating unit in a refinery, corrosion leakage occurred in the tee of the high-pressure air cooler inlet of the secondary reaction product, which seriously affected the long-term safe and stable operation of the unit. Analysis indicates that the primary cause of corrosion is insufficient water injection, which results in excessively high concentrations of ammonium hydrosulfide and chloride ions in the reactor effluent system. This condition readily induces ammonium chloride crystallization and deposition, subsequently leading to erosion-corrosion caused by ammonium chloride solutions. Meanwhile, the abrupt changes in flow velocity and flow pattern at locations such as elbows and tees further accelerate the corrosion process. By adjusting the water injection scheme and upgrading the materials, the corrosion rate at susceptible locations has been significantly reduced, while the corrosion of the piping between the first-stage and second-stage high-pressure air coolers has also been effectively mitigated. In addition, the paper proposes several protective measures to address the corrosion issues in the residue hydrotreating unit including strengthening feedstock management, adjusting the water injection scheme, upgrading materials in critical areas, and enhancing corrosion monitoring and inspection.

Key words: residue hydrotreating unitlhigh-pressure air coolerlcorrosion analysislanti-corrosion measures