Petrochemical industry is the downstream industry of the petroleum industry. It is a complex and huge industrial system, mainly including oil refining and production of ethylene , propylene, styrene, polyester, synthetic rubber, etc., as well as various chemicals that are further downstream. Corrosion in petrochemical industry includes electrochemical corrosion, chemical corrosion and local corrosion caused by it, atmospheric corrosion, soil corrosion, seawater corrosion and high temperature corrosion. Therefore, the petrochemical industry has various requirements for anti-corrosion coatings, which need to have excellent resistance to chemical atmosphere , salt spray erosion, soil corrosion, high temperature corrosion and acid and alkali resistance.
The coatings traditionally used in petrochemical industry are mostly alkyd resin coatings, chlorosulfonated polyethylene coatings, high chlorinated polyethylene coatings , epoxy coal tar pitch coatings, etc. Although the traditional anti-corrosion coating products have satisfactory anti- corrosion , the content of volatile organic compounds (VOC) is too high, red lead paint containing toxic heavy metals, and asphalt paint containing carcinogens are still widely used .
Now the petrochemical industry has put forward a new concept of heavy anti-corrosion: time saving, environmental protection and safety. Under this new concept, a series of new heavy corrosion coating products that are completely different from traditional anticorrosion coatings, such as epoxy zinc-rich, inorganic zinc silicate, epoxy cloud iron, aliphatic polyurethane , glass flake coatings, etc., have begun to be mass-produced. application. The new heavy-duty anti-corrosion coating has the characteristics of no heavy metal, no asphalt, low VOC, fast drying, low surface treatment, and thick film construction.
The application of low-VOC coatings such as solvent-free, high-solid and water-based heavy-duty anti-corrosion coatings can effectively solve the safety hazards caused by traditional solvent-based coatings in the current petrochemical industry coating process while . When painting a new steel structure workshop, the fast-drying paint system and thick-film construction coating can greatly shorten the painting time, speed up the painting of steel structures, the turnover of sites, and the transportation and installation of steel structures. The rapid coating of petrochemical plants during maintenance of anti-corrosion coating means shorter shutdown time and less painting man-hours, and the painted facilities can be restored to use in the shortest time.
Resistance to high-low temperatures is a common requirement in petroleum refineries. The temperature on the surface of the equipment may be the ambient temperature, or it may be the operating temperature of the equipment itself. Atmospheric temperature may range from minus tens of degrees Celsius in the north to over 40 degrees Celsius in the south. The operating temperature may range from -20°C to 538°C, such as the low temperature of the refrigeration system, or the high temperature on the boiler. Coating options in this range include epoxy, modified epoxy, phenolic, acrylic silicone, polyurethane, inorganic zinc, silicone, thermal induction, glass-filled inorganic, and more. For surfaces subject to rapid changes, the coating must also withstand thermal shock. If the paint cannot withstand the temperature, obvious damage will occur.
Painted surfaces are subject to erosion and erosion by airborne substances such as sand, charcoal or other media containing particulate matter. In the routine maintenance process, it will be squeezed by newly installed pipelines or valves, or the drop of other tools such as wrenches will also damage the coating. Slings can also cause damage to the coating when installing painted parts. The coating of inorganic zinc silicate coating is relatively hard. In the environment of pH=6~9, it can be used alone without topcoat; if topcoat is required, epoxy, acrylic, polyurethane, etc. are commonly used coatings.
Strong winds, temperature differences or pressure during processing can deform and bend components. For example, the floating roof of a large floating roof tank will deform up to 25.4cm under high-speed wind. During processing operations, the thin walls of containers expand and contract when heated and cooled. Therefore, the coefficient of thermal expansion should also be considered when choosing different coatings.
UV resistance and temperature extremes vary widely among different coatings. Coatings near the equator must be able to withstand strong radiation, and near the Arctic Circle, coatings must be able to withstand severe cold. Epoxy coatings are not resistant to ultraviolet rays and are easy to powder, so they are not easy to use as outdoor topcoats . Acrylic topcoats and aliphatic polyurethane topcoats are better choices.
The water resistance and solvent resistance of different coating films are very different, which has a great influence on the service life of the coating in a humid environment . In a high-humidity environment, the penetration of water will become greater. Hydrocarbon resin modified epoxy coatings, inorganic zinc silicate primers, polyamide epoxy coatings and aliphatic polyurethane topcoats are commonly used coating systems, and the dry film thickness is 150~200m . Radiation becomes very important. Coatings can be used to reduce or increase heat transfer to save energy. The heat reflectance of black is close to 0, the aluminum color and medium gray are between 40% and 50%, and the white is more than 80%.