Epoxy resins meet the requirements for drag-reducing inner coatings in long-distance natural gas pipelines

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Epoxy resins meet the requirements for anti-friction inner coatings in long-distance natural gas pipelines. 1. The coatings used for anti-friction inner layers in pipelines should possess the following characteristics: 1. The coating surface should be smooth and even. That is, the surface roughness of the coating should be low, so that the coating can provide an effective drag-reduction effect. “The \"West-to-East Gas Transmission\" project requires the average roughness of the coating surface to be less than 10μm. 　　 2. Wear resistance and hardness. Since drag-reducing coatings are relatively thin, typically only 38–80 μm, their good wear resistance and hardness ensure that they can withstand the wear caused by sand and cleaning devices inside the pipeline. 　　 3. Adhesion. Good adhesion ensures that the coating does not peel off during storage and transportation, bending, laying and line cleaning, as well as during operation. 　　 4. Voltage resistance. It can withstand repeated changes in air pressure and water pressure. 　　 5. Easy to paint. It can be applied using conventional spraying techniques under normal temperature and humidity conditions. 　　 6. Heat resistance. Since the application of the epoxy powder outer anti-corrosion coating to pipes requires a high temperature of around 240°C, if the \"inner first, then outer\" construction method is used, the inner coating must be able to withstand short-term high temperatures. II. Epoxy resin is the best film-forming base material for producing drag-reducing coatings. Epoxy resin is the ideal material for this purpose, and for gas transmission pipelines it possesses the following characteristics: 1. Excellent adhesion. The molecular structure of epoxy resins contains a large number of polar groups such as hydroxyl and ether groups. Additionally, during the curing process, the reactive epoxy groups can react with the metal atoms at the interface to form extremely strong chemical bonds, thereby enhancing the adhesion between the coating and the substrate. 　　2. Excellent wear and corrosion resistance. The benzene rings in the epoxy resin, along with the high cross-linking density of the cured coating, contribute to a coating that is hard, flexible, resistant to penetration, and durable against water and solvents. Furthermore, the high chemical stability of the ether bonds in the main chain structure contributes to the coating’s excellent resistance to acids and alkalis. 　　3. Able to withstand changes in pressure. Due to its low volume shrinkage rate of around 2% during curing, as well as its low coefficient of thermal expansion, the epoxy coating can withstand changes in temperature and stress. Additionally, the rigid benzene rings and flexible hydroxyl groups in its molecules ensure that the coating remains hard yet flexible after curing, resulting in excellent physical and mechanical properties.