Abstract: After two operation cycles and two major overhauls of ethylbenzene unit in a company，four corrosion forms were found：wet hydrogen sulfide corrosion，erosion corrosion by medium pressure steam condensate, weak acid corrosion, and low temperature dew point corrosion of air preheater of heating furnace. The causes for these corrosions were analyzed. It was concluded that the wet hydrogen sulfide corrosion, mainly existed in depropene system，was related to the content of hydrogen sulfide in catalytic dry gas; the erosion corrosion of medium pressure steam condensate mainly occurred at the elbow of pipeline，was related to material and process control; the weak acid corrosion in the cooling system on the top of non-aromatic tower，was related to device material and CO2 content of tower top gas; while the low temperature dew point corrosion in flue gas outlet of heat pipe pre-heater was related to process operation. Therefore, it is necessary to strengthen the monitoring of key parts, select material reasonably, and optimize operation conditions. After two operation cycles of the unit, the basic data has been accumulated for the parts prone to corrosion and thinning. Meanwhile, timely attention should be paid to the operation of similar units to ensure the stable long term operation.

Key words: ethylbenzene unit, wet hydrogen sulfide corrosion, condensate scour, weak acid corrosion, dew point corrosion, protection measures