Anti-corrosion scheme for steel structures

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There are a wide variety of steel structure types and the environments in which they find themselves. Even for the same steel structure facility, the anti-corrosion measures adopted vary depending on the conditions in different parts of it. Common large-scale steel structures include offshore oil platforms, bridges, television towers, high-voltage transmission towers, gates for large reservoirs, control panels, pipelines, and steel framework structures. These structures are exposed for long periods to corrosive environments such as chemical gases, industrial air, marine atmosphere, acidic water, and soil; therefore, to ensure their long-term use without the need for extensive repairs, it is necessary to apply appropriate anti-corrosion coatings to them. The specific coating scheme must be determined based on the corrosion environment and the properties of the media involved. Here, we provide recommendations for anti-corrosion coating schemes considering the operating environment of large-scale steel structures, the medium conditions in various parts of these structures, the requirements for surface treatment, and their operating conditions. A. Outdoor steel structures (chemical industrial atmosphere): For components that require sandblasting: BF-7005 epoxy zinc-rich primer (applied in 2–3 coats, with a thickness of 80–100 microns) + BF-7003 epoxy ferrochrome intermediate coat (applied in 2–3 coats, with a thickness of 100–120 microns) + BF-10005 fluorocarbon anti-corrosion topcoat or BF-4002 aliphatic polyurethane acrylic topcoat (applied in 2–3 coats, with a thickness of 80–100 microns); all of these products are two-component types. This coating system is designed for long-term corrosion protection in outdoor environments, and it represents an efficient anti-corrosion coating method recognized internationally. The BF-7005 primer provides excellent cathodic protection; the electrons generated during its use can effectively prevent the formation of iron oxide and stop the substrate from rusting ； The BF-7003 provides excellent shielding properties; chemical agents cannot penetrate vertically through this coating. Components coated with this material cannot have water or other substances penetrate to the underlying substrate, even when they remain submerged in water throughout their useful life ； The BF-10005 fluorocarbon coating is currently the one with the best weather resistance; this coating can be used on steel structures in harsh environments such as oil platforms, towers, and bridges. BF-4002 has weather resistance second only to that of BF-10005, but its service life still ranges from 10 to 15 years. BF-7005 epoxy zinc-rich primer (applied 2–3 times by brushing or spraying, with a thickness of 80–100 microns) + BF-7003 epoxy ferrochrome intermediate coat (applied 2–3 times by brushing or spraying, with a thickness of 100–120 microns) + BF-10002 high-chlorinated polyethylene heavy-duty anti-corrosion topcoat, or BF-10007 chlorinated rubber anti-corrosion coating, or BF-10012 chloroether anti-corrosion topcoat (applied 2–3 times by brushing or spraying, with a thickness of 80–100 microns). All of the topcoats BF-10002, BF-10007, and BF-10012 possess good acid resistance, especially in acidic industrial environments. These coatings can be used when the surface finish requirements for sandblasted steel structures are not particularly high, and there is no significant impact or friction involved. These coatings are single-component and easy to apply, but their aging resistance is lower than that of BF-4002 when evaluated solely through weathering tests. Additionally, BF-10012 being a new product, it has superior overall performance compared to the traditional BF-10002 and BF-10007. For components that are not sandblasted: BF-7025 two-component, fast-drying epoxy iron oxide rust-inhibiting primer (applied by brushing or spraying 2–3 times, with a thickness of 80–100 microns) + BF-7003 epoxy limonite intermediate coat (applied by brushing or spraying 2–3 times, with a thickness of 100–120 microns) + BF-4002 acrylic aliphatic polyurethane topcoat or BF-10005 fluorocarbon anti-corrosion topcoat (applied by brushing or spraying 2–3 times, with a thickness of 80–100 microns); all of these are two-component products. Alternatively, BF-7025 two-component, fast-drying epoxy iron oxide rust-inhibiting primer (applied by brushing or spraying 2–3 times, with a thickness of 80–100 microns) + BF-7003 epoxy limonite intermediate coat (applied by brushing or spraying 2–3 times, with a thickness of 100–120 microns) + BF-10002 high-chlorinated polyethylene heavy-duty anti-corrosion topcoat, or BF-10007 chlorinated rubber anti-corrosion topcoat, or BF-10012 chloroether anti-corrosion topcoat; all of these topcoats are single-component products (applied by brushing or spraying 2–3 times, with a thickness of 80–100 microns). Sandblasting has a very significant effect on enhancing the corrosion resistance of steel structures; the anti-corrosion performance of steel structures that have been sandblasted is significantly better than that of those that have not been sandblasted. However, factors such as processing costs, manufacturing processes, and the shape of the steel structures limit the widespread use of sandblasting. This solution is an outdoor long-term corrosion protection coating system, particularly suitable for corrosion protection coating in conditions without sandblasting. Note: For components that are not sandblasted, if the corrosion type in the atmospheric environment is C3 (moderate) or lower, it is not necessary to use the BF-7003 epoxy limonite intermediate coat. BF-10002 high-chlorinated polyethylene primer + BF-10002 topcoat (2–3 coats of each, applied by brushing or spraying, with a thickness of 80–100 microns; total thickness should be no less than 150 microns). BF-10012 chloroether-based anti-corrosion coating topcoat + BF-10012 topcoat (2–3 coats of each, applied by brushing or spraying, with a thickness of 80–100 microns; total thickness should be no less than 150 microns). These coatings are single-component solvent-based products that offer good resistance to various chemicals and weathering conditions. They are easy to apply and represent high-performance anti-corrosion and decorative coatings. The fluorosilicone rubber contained in these coatings enhances both the toughness of the resin and its resistance to chemicals and weathering. This coating system can withstand strong acids such as high-concentration hydrofluoric acid; however, its durability in outdoor conditions is slightly inferior to that of acrylic aliphatic polyurethane topcoats and fluorocarbon anti-corrosion topcoats. The adhesion of this type of primer to the substrate is inferior to that of epoxy rust-inhibiting primers; it is suitable for steel structures that are not subject to significant vibration, friction, or impact.