关键词: 常减压, 常顶换热器, 腐蚀, 氯化铵

Abstract: When the atmospheric and vacuum distillation unit of a refining and chemical enterprise is shut down for maintenance, it was found that there are dense pits corrosion near the E-301A/B/C tubesheet diaphragm groove of crude oil-atmospheric top oil gas heat exchanger. The corrosion pits are connected into pieces with heavy corrosion. From the aspects of E-301A/B/C tubesheet corrosion morphology, atmospheric and vacuum crude oil propertiess, and atmospheric and vacuum acid water properties, it is inferred that the dew point corrosion area is from the atmospheric tower top to the outlet of E-301A/B/C by calculating the atmospheric top dew point and salt deposition point. As E-301A/B/C is set in parallel, the water injection is unevenly distributed, especially when the water flow of the injection system is small or the total amount of water injection is insufficient. Ammonium chloride cannot be fully dissolved by water and is taken away by the gas-phase medium. It is deposited in the “dead zone” such as the diaphragm groove, resulting in an increased risk of corrosion under the scale. Therefore, it is judged that the main reason for the corrosion of E-301A/B/C tubesheet diaphragm groove is the corrosion under the scale of ammonium chloride. It is suggested to reduce the corrosion under the scale of ammonium chloride by appropriately increasing the operating temperature of the atmospheric tower top, stopping or reducing the cold reflux flow at the tower top, and improving the water injection at the tower top.

Key words: atmospheric and vacuum unit, atmospheric tower top oil gas heat exchanger, corrosion, ammonium chloride