Severe corrosion of the shell and tube exchangers in the vacuum distillation units of the petrochemical industry
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The image below shows the shell and tube box of the vacuum distillation unit in petrochemical industries, specifically the overhead vacuum pre-condenser. Model: FLB1200-395-16-4, Material: 10# steel. This heat exchanger shell has been in operation for nearly 5 years. Operating conditions: Shell side: oil, vapor, and water vapor, temperature 55°C, pressure negative. Process conditions: medium, deep well water, temperature 23°C, pressure 0.2 MPa. During maintenance, when the condenser was opened, it was found that the surface of the tube bank on the oil, vapor, and steam side was severely corroded, with some partitions already perforated.
The main reasons for the severe corrosion of the tube sheet in this heat exchanger shell may be as follows: 1. Condensation corrosion – During operation, a mixture of oil, steam, and water vapor condenses on the tube sheet side under negative pressure at 55°C, resulting in acidic condensate (such as condensate containing H_2S, CO_2, and organic acids). This acidic fluid causes severe corrosion to the 10# steel material. 2. Poor corrosion resistance of the material: The currently used 10# carbon steel has low inherent corrosion resistance, and it is prone to erosion or localized perforation corrosion in environments containing acidic components. 3. Unstable operating conditions of the heat exchanger lead to the continuous accumulation of acidic dew. Prolonged low-temperature conditions (around 55°C) along with negative pressure facilitate the condensation and deposition of corrosive substances, which then remain in contact with the metal surface and accelerate corrosion. Suggestions for improvement measures: 1. Replace with corrosion-resistant materials, such as 316L stainless steel or composite steel plates. 2. Optimize operating conditions during use to reduce acidic dew formation. 3. Apply anti-corrosion coatings or linings to minimize corrosion damage. 4. Conduct regular inspections and monitoring, or carry out periodic cleaning, to prevent the accumulation of corrosion products.