There are various factors that cause corrosion of steel structures, mainly electrochemical corrosion. Once the steel structure is corroded, it will become more and more serious. In this way, the cross-sectional area of the component will be reduced, the bearing capacity will be reduced, and it will gradually lose its use value and be scrapped. Although the corrosion of steel structures in use is not always avoided, the rate of corrosion can be controlled, which requires effective anti-corrosion measures for steel structures.

Corrosion characteristics of steel structure: After the steel structure is shot blasting, press forming, electric welding assembly and other processes, the thermal stress distribution of the steel structure is uneven or grain deformation is caused, which causes the difference in the internal electric potential of the steel structure, which is the cause of corrosion of the steel structure. "Hidden danger", which is the reason why the electric weld of steel structure is particularly prone to rust.

Metal surface treatment is caused by various internal and external factors. To sum up, the main factors affecting metal corrosion are as follows.

The influence of the metal material itself

Different metals have different electrical potentials and different metallographic structures, and their stability (that is, corrosion resistance) is different, and steels with the same chemical composition have different corrosion resistance due to different heat treatment processes. In addition, the uneven distribution of thermal stress in the process of forging, casting, electric welding, or the deformation of grains in the process of thermal processing, etc., may cause differences in the electric potential inside the metal and accelerate the corrosion of the metal itself.

Metal surface finish state

It also has a significant effect on the corrosion rate. Especially in the initial stage, the smoother the metal surface, the better the corrosion resistance. The rough metal surface becomes positive because the deep concave part is not easily accessible to oxygen, and the surface becomes negative, resulting in corrosion of the oxygen concentration cell.

Influence of ambient temperature

- In general, as the temperature increases, the corrosion rate of metals in the electrolyte solution increases. For example, for every 10°C rise in seawater temperature, the corrosion rate of steel will double, because the electrical reaction strengthens as the temperature rises. In addition, in areas with continental climates, the temperature difference between day and night is large, and the relative humidity in the atmosphere at night increases again, and the moisture in the air will condense on the metal surface in the form of condensation, providing conditions for the metal to rust.

The effect of the composition and concentration of the solution

For example, seawater is a natural electrolyte solution with various salts, which also contains organisms, sediment, dissolved gas, corrupt organic matter, and the like. However, the important factor affecting the corrosion rate of steel is the salinity of seawater, high salinity, high electrical conductivity, the corrosion current intensity of the macro battery becomes larger, and the corrosion of steel is intensified. In addition, the large amount of chloride ions in seawater will hinder or even destroy the passivation of metals and promote the corrosion of metals.

Corrosive media and other factors

Various corrosive media and other factors will also accelerate the corrosion of metals. Because in addition to O2 and H2, the atmosphere also contains N2 and various sundries, such as salt spray near the ocean, SO2, H2S in the chemical industry, and various soot, metal compounds and other salt particles, etc. These corrosive Once the medium falls on the metal surface, it will condense with moisture, accelerating the corrosion of the metal.