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

摘要： 某炼化企业常减压装置在停工检修时发现，原油-常顶（常压塔塔顶）油气换热器E-301A/B/C管板隔板槽附近区域存在密集蚀坑，蚀坑连接成片，腐蚀较重。从E-301A/B/C管板腐蚀形貌、常减压原油性质、常顶酸性水性质等方面出发，通过计算常顶露点和结盐点等手段，推断出发生露点腐蚀的区域在常顶至E-301A/B/C出口。由于E-301A/B/C为并联设置，注水量分布不均，尤其在注入系统水流量较小或注水总量不足时更加明显。氯化铵无法被水充分溶解并被气相介质带走，沉积在隔板槽等死区部位，导致垢下腐蚀风险增大，因此判断造成E-301A/B/C管板隔板槽腐蚀的主要原因是氯化铵垢下腐蚀。建议通过适当提高常顶操作温度、停用或减少塔顶冷回流流量、改善塔顶注水等措施来减缓氯化铵垢下腐蚀。

关键词: 常减压, 常顶换热器, 腐蚀, 氯化铵