Corrosion prevention measures for steel structures
(1) weather resistant steel: steel with better corrosion resistance than general structural steel is called weather resistant steel, which generally contains phosphorus, copper, nickel, chromium, titanium and other metals, so that a protective layer is formed on the metal surface to improve corrosion resistance. Its low-temperature impact toughness is also better than that of general structural steel. The standard is "weathering steel for welded structures" (GB)
(2) hot dip galvanizing: hot dip galvanizing is to immerse the steel members after rust removal into the molten zinc melted at a high temperature of about 600 ℃, so that the surface of the steel members is attached with a zinc layer. The thickness of the zinc layer shall not be less than 65 m for thin plates below 5mm, and not less than 86 m for thick plates, so as to achieve the purpose of corrosion prevention. The advantages of this method are long durability, high industrialization and stable quality. Therefore, it is widely used in outdoor steel structures that are seriously corroded by the atmosphere and difficult to maintain. Such as a large number of transmission towers, communication towers, etc. In recent years, a large number of profiled steel plates in light steel structure system have appeared. Thermal (2) local stress-strain method is also widely used, which is mainly used to calculate the low cycle fatigue life dominated by plastic deformation. Zinc immersion is used to prevent corrosion. The first process of hot-dip galvanizing is acid pickling and rust removal, followed by cleaning. The incompleteness of these two processes will leave hidden dangers for the corrosion prevention of more than 3/4 hot air plastic granulator. So we must deal with it thoroughly. For steel structure designers, they should avoid designing components with mating surfaces, so as to avoid incomplete pickling or unclean acid washing in the gaps of mating surfaces. The test results of non-standard plating state should consider this factor in the design to reflect the phenomenon of yellow water flowing on the zinc surface. Hot dip galvanizing is carried out at high temperature. For tubular members, both ends should be open. If both ends are closed, the air in the pipe will expand and the head plate will burst, resulting in safety accidents. If one end is closed, the flow of zinc liquid is not smooth, and it is easy to accumulate in the tube
(3) thermal sprayed aluminum (zinc) composite coating: This is a long-term anti-corrosion method with the same anti-corrosion effect as hot-dip galvanizing. The specific method is to remove the rust on the surface of steel members by sandblasting first, so that the surface shows metallic luster and roughens. Then use acetylene oxygen flame to melt the continuously sent aluminum (zinc) wire, and blow it to the surface of steel members with compressed air to form a honeycomb aluminum (zinc) coating (thickness about 80 m ~ 100 m). Finally, the pores are filled with epoxy resin or neoprene paint to form a composite coating. This method cannot be applied to the inner wall of the tubular member, so both ends of the tubular member must be sealed airtight so that the inner wall will not be corroded. The advantage of this process is that it has strong adaptability to the size of components. As the leader of 3D printing modified materials in the world, Jin Min has almost no restrictions on the shape and size of components. Ship locks as large as Gezhouba dam are also constructed in this way. Another advantage is that the thermal effect of this process is local and constrained, so it will not produce thermal deformation. Compared with hot-dip galvanizing, this method is less industrialized, the labor intensity of sand blasting and aluminum (zinc) spraying is high, and the quality is also easily affected by the emotional changes of operators
(4) coating method: the corrosion resistance of coating method is generally not as good as that of long-term corrosion prevention method (but at present, the anti-corrosion life of fluorocarbon coating can even reach 50 years). Therefore, there are many indoor steel structures or outdoor steel structures that are relatively easy to maintain. It has low cost at one time, but its maintenance cost is high when it is used outdoors. The first step in the construction of coating method is rust removal. High quality coating depends on thorough rust removal. Therefore, the coating with high requirements generally uses sand blasting and shot blasting to remove rust, expose the luster of metal, and remove all rust and oil stains. The coating applied on site can be derusted manually. The choice of coating should consider the surrounding environment. Different coatings have different resistance to different corrosion conditions. The coating is generally divided into primer (layer) and finish (layer). The primer contains more powder and less base material. The film is rough, with strong adhesion to steel and good adhesion to finish paint. The topcoat has many base materials, and the film is glossy, which can protect the primer from atmospheric corrosion and resist weathering. There is a problem of compatibility between different coatings. Pay attention to their compatibility when choosing different coatings before and after. The construction of coating should have appropriate temperature (between 5 ~ 38 ℃) and humidity (relative humidity not greater than 85%). The dust in the construction environment of the coating shall be less, and there shall be no condensation on the component surface. No rain is allowed within 4 hours after painting. The coating is generally done for 4 ~ 5 times. The total thickness of dry paint film is 150 m for outdoor works and 125 m for indoor works, and the allowable deviation is 25 m. The total thickness of dry paint film can be thickened to 200 ~ 220 m at the sea or in the highly corrosive atmosphere.
(5) cathodic protection method: add more active metal on the surface of steel structure to replace the corrosion of steel. It is often used in underwater or underground structures