Abstract: In order to explore the reasons for the corrosion failure and leakage of the high-pressure heat exchanger tube bundles of a hydrogenation unit, the dew point temperature, ammonium chloride crystallization temperature, ammonium chloride deliquescent temperature and relative humidity of the cold low pressure separator oil phase stream were calculated by Aspen Plus process simulation software when the water mass fractions were 1%，2% and 3%. It is found that compared with the empirical dew point temperature prediction method, the method of judging the corrosion risk area under ammonium chloride scale by introducing the deliquescent point and dividing the "wet environment" temperature range is more suitable for actual corrosion cases. The "wet environment" areas are determined as 50-103 ℃, 50-161 ℃ and 50-176 ℃ in the case of 3 kinds of oil phase water content,respectivily. In addition, with the increase of water content in the oil phase, the corrosion area in the "wet environment" will gradually migrate to the high temperature part,and the ammonium chloride salt corrosion is expected to become more severe.

Key words: cold low pressure separator, oil phase, NH4Cl, deliquescence, corrosion, relative humidity