Objective Aiming at controlling the risks of processing high-sulfur feedstock in hydrocracking unit, production problems are comprehensively summarized and the corrosion causes of REAC system are emphatically analyzed.

Methods The main parameters affecting the corrosion of REAC system were calculated item by item which was subsequently compared with the design specifications or related studies.

Results It can be seen from the analysis that the increase in the volume fraction of H₂S in circulating gas would result in the increase of the corrosion factor K_p and H₂S partial pressure of REAC system, which ultimately enhance the corrosion of REAC air cooling tube bundle and the outlet elbow.

Conclusions The processing of high-sulfur feedstock has serious adverse effects on the smooth operation of hydrocracking unit in long term. Several suggestions were given as follows: (1) Straight-run diesel with low sulfur content should be added into hydrocracking feedstock when the product diesel demand drops, so as to increase jet fuel and tail oil, reduce diesel-gasoline ratio, and meanwhile reduce sulfur contents of feedstock; (2) The volume fraction of H₂S in circulating gas should be strictly controlled during production operation to ensure the corrosion factor K_p < 0.2.