Analysis on the corrosion failure of U-tube heat exchanger in hydrogenation unit

Unscheduled shutdown often occurs in diesel hydrogenation unit due to the corrosion leakage of heat exchanger. After a series of analyses of technological and flow processes, failure causes of the U-tube heat exchanger were investigated. The inside and outside mediums of heat exchanger tubes were hot high-pressure separation (HHPS) gas and cold low-pressure separation oil, respectively. A detailed examination shows that the corrosion occurs in shell side and was caused by under-deposit corrosion of NH4Cl. Through the numerical simulation, it is found that the leakage location is at the place where water tends to accumulate. Thus, in order to prevent the corrosion of heat exchanger, the water content carried in the cold low-pressure separation oil should be reduced.