Coating treatment method for tube sheet of tubular petrochemical heat exchangers

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Coating treatment methods for the tube sheet of shell-and-tube petrochemical heat exchangers 1. Overview: Shell-and-tube heat exchangers are widely used in chemical production to carry out heat exchange of materials. The materials used for heat exchangers are generally carbon steel, stainless steel, and copper. In the case of carbon steel tube sheets used as coolers, corrosion and leakage at the welds between the tube sheet and the tubes often occur, which severely affects safe production. Leakages into the cooling water system contaminate the environment and cause material waste. Problems of this kind are well resolved by applying polymer coatings to the tube sheet surface, which extends its service life. 2. Corrosion mechanism of tube sheet welds: In the fabrication of shell and tube heat exchangers, the welding of the tube sheet to the tubes is generally carried out using manual arc welding. The welds suffer from various defects to varying degrees, such as depressions, pores, and slag inclusions, and the stress distribution within the welds is also uneven. During use, the tube sheet area is generally in contact with industrial cooling water, and the impurities, salts, gases, and microorganisms present in this water can cause corrosion to the tube sheet and welds. Research shows that industrial water, whether freshwater or seawater, contains various ions and dissolved oxygen; changes in the concentrations of chloride ions and oxygen play an important role in determining the pattern of metal corrosion. Furthermore, the complexity of the metal structure also affects the corrosion pattern. Therefore, the corrosion of the tube sheet and tube sheet-to-tube welds is mainly pitting and crevice corrosion. Visually, the tube sheet surface is covered with numerous corrosion products and deposits, along with rust pits of varying sizes. 3. Coating treatment of the tube sheet surface: An effective way to prevent corrosion at the welds between the tube sheet and the tubes is to isolate the surface of the tube sheet from water, that is, by applying a protective layer to the metal surface. Corrosion-resistant coatings resistant to circulating water such as silicone epoxy and epoxy furan can be used. It is recommended to use materials with a room-temperature curing system.