(1) Corrosion resistance:
Its low-temperature impact toughness is also better than general structural steel. The standard is weathering steel for welded structure.
(2) Hot-dip galvanizing:
Hot-dip galvanizing is to immerse the derusted steel components in a zinc solution melted at a high temperature of about 600℃, so that the surface of the steel components is attached with a zinc layer.
The thickness of the zinc layer should not be less than 65μm for thin plates below 5mm. The board is not smaller than 86μm.
So as to play the purpose of anti-corrosion. The advantages of this method are long durability, high degree of industrialization, and stable quality.
Therefore, it is widely used in outdoor steel structures that are severely corroded by the atmosphere and difficult to repair.
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 systems have appeared. Hot-dip zinc is also used to prevent corrosion.
The first process of hot-dip galvanizing is pickling and rust removal, followed by cleaning. Incomplete two processes will leave hidden dangers to corrosion prevention.
So it must be handled thoroughly. For steel structure designers, it is necessary to avoid designing components with mating surfaces, so as to avoid incomplete pickling in the gaps of the mating surfaces or incomplete acid cleaning.
Causes the phenomenon of yellow water flowing on the galvanized surface. Hot-dip galvanizing is performed at high temperature.
For tubular members, both ends should be open. If the two ends are closed, the air in the pipe will expand and the head plate will burst, which will cause a safety accident.
If one end is closed, the zinc liquid will not flow smoothly and will easily accumulate in the tube.
(3) Thermal spray aluminum (zinc) composite coating:
This is a long-term anti-corrosion method equivalent to that of hot-dip zinc. The specific method is to first sandblast the surface of the steel component to remove the rust to expose the metallic luster and rough the surface.
Then use an acetylene-oxygen flame to melt the continuously sent aluminum (zinc) wire, and blow it with compressed air to the surface of the steel member to form a honeycomb-shaped aluminum (zinc) spray layer (thickness about 80μm-100μm).
Finally, the capillary pores are filled with paint such as 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 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 component, and the shape and size of the component are almost unlimited. Ship locks as large as Gezhouba were also constructed in this way. Another advantage is that the thermal effect of this process is local and constrained, so there is no thermal deformation.
Compared with hot-dip galvanizing, this method has a lower degree of industrialization, and the labor intensity of sandblasting aluminum (zinc) is large, and the quality is also easily affected by the emotional changes of the operator.
The corrosion resistance of the coating is generally not as good as the long-term anti-corrosion method.
Therefore, it is used for indoor steel structures or outdoor steel structures that are relatively easy to maintain. It has low cost once, but high maintenance cost when used outdoors.
The first step of coating construction is to remove rust. A high-quality coating depends on thorough derusting.
Therefore, high-demand coatings generally use sandblasting to remove rust, revealing the luster of the metal, and removing 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 topcoat (layer). The primer contains more powder and less base.
Rough film formation, strong adhesion to steel, and good bonding with topcoat.
The topcoat has many base materials, has a glossy film, can protect the primer from atmospheric corrosion, and can resist weathering. There is a problem of compatibility between different coatings.
When choosing different coatings before and after, pay attention to their compatibility. The construction of the coating should have a 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 component. No rain shall be allowed within 4 hours after painting.
The coating is generally done 4 to 5 times. The total thickness of the dry paint film is 150μm for outdoor projects and 125μm for indoor projects, with an allowable deviation of 25μm.
The total thickness of the dry paint film can be thickened to 200~220μm on the seaside or sea or in a strongly corrosive atmosphere.
Add more active metal to the surface of steel structure to replace steel corrosion. Often used in underwater or underground structures.