Functions and requirements of the anti-corrosion coating on carbon steel water coolers

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This post was last edited by Wang Wei2 on 2023-11-24 at 12:43. Functions and requirements of the anti-corrosion coating for carbon steel water coolers 1. Background Carbon steel cooling equipment is one of the essential devices in petrochemical enterprises. Corrosion and scaling in carbon steel heat exchangers, as well as the resulting decline in heat transfer efficiency and tube bundle leakage, severely affect the normal production and profitability of enterprises. 2. The function of the anti-corrosion coating on carbon steel water coolers: Corrosion and scaling of carbon steel water coolers have always been problems that are difficult for petrochemical companies to resolve. There are many methods to prevent corrosion, such as proper material selection, rational design, electrochemical protection, surface coatings, improving operating conditions, the use of corrosion inhibitors, and scientific management. Using stainless steel tube bundles is too costly, and the Cl‑ ions in the medium will damage the passivation film, resulting in poor performance. The application technology of electrochemical protection in heat exchange equipment in refineries is not yet mature. Considering both the comprehensive protection effects and economic benefits, using a non-metallic coating (paint) is a better approach. 3. Coating requirements: The anti-corrosion principle of non-metallic coatings is to isolate metal equipment from corrosive agents; it not only improves corrosion resistance but also helps to save a large amount of precious metals and alloys. Coatings should meet the following requirements: (1) The coating itself must be resistant to corrosion in the surrounding medium. (2) It has a tight structure, is completely pore-free, and cannot be penetrated by the medium. (3) It has a strong bonding force with the base metal. (4) It is evenly distributed over the entire protective surface and has a certain thickness. (5) For the heat exchanger core, it should also have little impact on heat transfer efficiency and possess scale-inhibiting properties. 4. Application of coating protection for carbon steel cold exchange equipment: The painting process for the cores of carbon steel water coolers is carried out in strict compliance with two standards issued by Sinopec Corporation: the \"Interim Provisions on Anti-corrosion Coatings for Carbon Steel Water Coolers\" and the \"Interim Provisions on Quality Inspection of Anti-corrosion Coatings for Carbon Steel Water Coolers\". By strictly controlling the quality of paint production and coating processes, the average service life of the water cooler cores has been increased from two years in the past to over four years, with excellent results and stable operation over the past few years. The following is a comparison of the performance of carbon steel coolers TH-847 with coated protection and those without coating: (1) Coolers without any protection: After one production cycle, severe corrosion and scaling occur on the inner walls of the tubes, with the scale thickness exceeding 3 mm; even after maintenance, they can only be used for another cycle. The corrosion and scaling of carbon steel coolers pose a range of difficulties in production and maintenance, while also affecting the economic efficiency of enterprises. a. Corrosion leads to perforation and leakage; a single tube bundle can only be used for two cycles (22 months), resulting in a short service life for the equipment. b. Corrosion and leakage affect the stability of production and product quality. c. Scaling affects the cooling efficiency of the medium, resulting in a decrease in product yield. d. When scaling is severe, the coolant cannot circulate, preventing the medium from being cooled; as a contingency measure, cooling water is often used to spray the cooler housing for cooling. It not only causes corrosion of the casing but also affects the on-site environment of the equipment. When scaling is particularly severe, it can even affect the normal progress of production. e. Severe scaling makes maintenance difficult; manually passing through the areas affected is not only dirty and labor-intensive but also often hinders the progress and quality of maintenance work. (2) The water-cooler cores protected with a TH-847 coating remained in good condition after one production cycle, showing no defects, corrosion, and maintaining excellent performance. Coating protection offers the following benefits: a. It provides good cooling effects, ensures smooth process operation, and enhances the economic efficiency of enterprises. B. The inner wall of the pipe has slight scaling, which can be removed using water at a pressure of 6 kg/cm2. Maintenance is time and labor-saving, with high quality. b. It extends the service life of the equipment; the coated tube bundles can be used for at least four years. Taking a Ф900 cooler as an example: the price of the tube bundle is 7,000 yuan per ton × 4.7 tons = 32,900 yuan; over a period of two years, this amount is spread out to 16,450 yuan per year. The cost of coating protection is 85 yuan/m2 × 240 m2 = 20,400 yuan. Assuming the protection lasts for four years, the annual cost is 13,325 yuan. In comparison, installing a Ф900 cooler saves the enterprise an average of 3,135 yuan per year, which is equivalent to 14 yuan per m2 per year. The indirect economic benefits resulting from reduced downtime for repairs, shorter maintenance times, improved product quality, and higher product yields are also considerable.