Which anti-corrosion steels are used in general steel structures?

In fact, in the steel structure, in addition to the hardness, there are also high requirements for the anti-corrosion performance of the selected materials. Let's briefly talk about the common anti-corrosion steel building materials used in steel structure houses.

(1) Weathering steel: Steel whose corrosion resistance is better than general structural steel is called weathering steel. It generally contains phosphorus, copper, nickel, chromium, titanium and other metals to form a protective layer 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 (GB4172-84).

(2) Hot-dip galvanizing: Hot-dip galvanizing is to immerse the rust-removed steel components in a molten zinc solution at a high temperature of about 600 °C, so that the surface of the steel components is attached with a zinc layer, and the thickness of the zinc layer is less than 5mm. The thin plate shall not be less than 65μm, and the thick plate shall not be less than 86μm. So as to achieve the purpose of anti-corrosion. The advantages of this method are long durability, high degree of industrialization of production and stable quality. Therefore, it is widely used in outdoor steel structures that are severely 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 the light steel structure system have appeared. Hot dip galvanizing is also used to prevent corrosion. The first process of hot dip galvanizing is pickling and rust removal, followed by cleaning. Incompleteness of these two processes will leave hidden dangers to corrosion protection. So it has to be dealt with completely. For the steel structure designer, it should be avoided to design components with a mating surface, so as to avoid incomplete pickling or acid cleaning in the gap of the mating surface. Causes the phenomenon of yellow water flowing on the galvanized surface. Hot dip galvanizing is carried out at high temperature. Tubular elements should be left open at both ends. If both ends are closed, the air in the pipe will expand and the head plate will burst, resulting in an accident. If one end is closed, the zinc liquid will not flow smoothly and easily accumulate in the tube.

(3) Thermal spray aluminum (zinc) composite coating: This is an anti-corrosion method that has a long-term effect with the anti-corrosion effect of hot-dip galvanizing. The specific method is to first blast the surface of the steel component to remove rust, so that the surface is exposed to metallic luster and roughened. Then, the continuously sent aluminum (zinc) wire is melted with acetylene-oxygen flame, and blown onto the surface of the steel member with compressed air to form a honeycomb-shaped aluminum (zinc) sprayed layer (thickness of about 80μm~100μm). Finally fill the capillaries with paint such as epoxy or neoprene paint to form a composite coating. This method cannot be constructed on the inner wall of the tubular member, so both ends of the tubular member must be airtightly sealed so that the inner wall will not corrode. The advantage of this process is that it has strong adaptability to the size of the components, and the shape and size of the components are almost unlimited. Ship locks as large as Gezhouba are also constructed in this way. Another advantage is that the thermal impact of this process is localized and constrained, so no thermal deformation occurs. Compared with hot-dip galvanizing, this method is less industrialized, sandblasting aluminum (zinc) is labor-intensive, and the quality is also easily affected by the operator's emotional changes.

(4) Coating method: The anti-corrosion method of the coating method is generally not as good as the anti-corrosion method with a long-term effect (but the anti-corrosion period of the current 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 is low cost once, but higher maintenance when used outdoors. The first step in the construction of the coating method is rust removal. Better coatings rely on complete rust removal. Therefore, the coatings with high requirements generally use sandblasting and shot blasting to remove rust, reveal the luster of the metal, and remove all rust and oil stains. Coatings applied on site can be rust removed by hand. The choice of coating should consider the surrounding environment. Different coatings have different resistance to different corrosion conditions. Coatings are generally divided into primers (layers) and topcoats (layers). The primer contains more powder and less base. Rough film formation, strong adhesion to steel, and good combination with topcoat. The topcoat has many base materials, and the film is glossy, which can protect the primer from atmospheric corrosion and 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 the coating should have proper temperature (between 5~38℃) and humidity (relative humidity not more than 85%). The construction environment of the coating should be less dusty, and there should be no condensation on the surface of the components. Do not expose to rain within 4 hours after painting. The coating is generally done 4 to 5 times. The total thickness of dry paint film is 150μm for outdoor projects and 125μm for indoor projects, and the allowable deviation is 25μm. At the seaside or sea or in a strong corrosive atmosphere, the total thickness of the dry paint film can be thickened to 200~220μm.

(5) Cathodic protection method: add more active metal to the surface of the steel structure to replace the corrosion of the steel. Often used in underwater or underground structures.

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