Discussion on the corrosion problem in the top reductor of an atmospheric pressure distillation tower
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It is the tube bundle of the top fractionator in an atmospheric pressure distillation tower; the inner wall of this tube bundle is severely corroded. Circulating water flows around the outer wall of the tubes, while an oil-based fluid containing about 0.5% water flows inside them. The operating conditions are as follows: the temperature at the top of the tower is 170–180°C, the temperature at the top of the fractionator is 110–120°C, and the pressure on the inner wall of the tube bundle is at atmospheric pressure. The tube bundle material is S2205, with a tube diameter of DN32*2.5. After being in use for about 2 years, the inner wall of the tubes suffered from grooved corrosion or erosion-induced thinning, with the thinned areas located 300–1000 mm from the bottom of the reducer. See the figure below for details:
The possible reasons for corrosion on the inner wall of the reductor tube bundle are as follows: 1. **Temperature effects**: The temperature at the top of the tower is relatively high, ranging from 170 to 180°C. This can cause water in the oil-based medium to vaporize, and then to condense in areas with lower temperatures (110–120°C), leading to an increase in the concentration of acidic substances locally and thus accelerating corrosion. 2. **Material issues**: Although S2205 duplex stainless steel possesses good corrosion resistance, its resistance to pitting and stress corrosion cracking may decrease in high-temperature environments with the presence of chloride ions. 3. **Medium factors**: The oil medium flowing within the tube bundle contains about 0.5% water, and this small amount of water can easily turn into a corrosive agent at high temperatures, especially when corrosive chemicals such as sulfides and chlorides are present. 4. **Flow velocity and erosion effect**: The flow of oil in pipelines can lead to erosion, especially at bends or changes in pipe diameter; variations in flow velocity can result in more intense erosion, accelerating local wear and corrosion of the material. To address these issues, the following measures are recommended: - **Optimize operating conditions**: Adjust the temperatures at the top of the tower and in the reductor to minimize water evaporation at high temperatures and condensation at low temperatures. - **Improved materials**: Consider using materials with better corrosion resistance, such as higher-grade stainless steel or corrosion-resistant coatings. - **Strengthen monitoring**: Regularly inspect and monitor the corrosion of the tubes, especially in areas prone to corrosion, and carry out repairs or replacements promptly. - **Optimized design**: Improve the piping design to reduce dead zones and lower the likelihood of erosion. .
Thank you for sharing. The circulating water has white foam; the reason is unknown. https://bbs.hcbbs.com/thread-5669817-1-1.html (Source: Haichuan Chemical Industry Forum). The circulating water in the circulating water system is yellow, similar to the color of the Yellow River. https://bbs.hcbbs.com/thread-5667515-1-1.html (Source: Haichuan Chemical Industry Forum)
Can changing the tube bundle material to 904L solve the aforementioned corrosion problem?