It is well known that steel structures are easily corroded in humid environment. Oxygen and water in atmosphere are important factors causing corrosion of steel structures in civil buildings. Besides, some industrial gases such as SO2, CO2, NO2 can also cause corrosion of steel structures. The anticorrosion requirements of building steel structure are not only related to its environmental conditions, but also to the concrete material, structure form, use requirements, construction conditions and maintenance and management conditions of building materials. These are all factors that should be considered in anticorrosion design and construction.
Generally speaking, in anticorrosion design, first of all, according to the importance of buildings, environmental corrosion conditions, construction and maintenance conditions and other requirements to determine the reasonable design life of anticorrosion, and then comprehensive consideration of various factors, including economy, according to local conditions, reasonable selection of anticorrosion programs.
It is worth noting that the protection should be strengthened in the parts where the important load-bearing structural components and maintenance are difficult. If they are in the use environment of serious corrosion, isolation measures such as weatherproof steel or encased concrete should be adopted. In the Code for the Design of Steel Structures, there are clear and detailed requirements for the anticorrosion design of steel structures. In recent years, the state has promulgated and implemented more than ten relevant codes and standards for various building forms, different anti-corrosion methods and construction techniques, so that the anti-corrosion design, construction and acceptance of steel structures can be based on.
Anti-Corrosion Scheme for Steel Structures
The existing anti-corrosion schemes for steel structures can be divided into the following categories, which can be used separately or in combination in design:
Weatherproof steel
Weatherproof steel, namely atmospheric corrosion steel, is a series of low alloy steel between ordinary steel and stainless steel. Weatherproof steel is 2 to 8 times of ordinary steel, and its coatability is 1.5 to 10 times of ordinary steel. It has good rust resistance. It is mainly used in railway, vehicles, bridges, towers and other structures exposed to the atmosphere for a long time. Weatherproof steel is also used in building structures, but it is seldom used in residential buildings. Fig. 1 below is the Zhongfa Center of Tongji University. Its exterior walls and sloping roofs are made of weatherproof steel. Fig. 2 is the Chicago City Center. Its giant steel column is made of Cotton steel, which is also a kind of weathering steel.
Cathodic Protection Measures
Cathodic protection measures are based on the principle of electrochemistry, which can replace the corrosion of steel by adding more active metals to the surface of steel structures. They are usually applicable to underwater or underground structures.
Anticorrosive coatings-zinc, aluminium and other metal protective coatings formed by various processes
As you can see, the transmission tower is also steel structure, but never rusted. The steel structure treated by hot-dip galvanizing has a long anti-corrosion life. The methods of long-term corrosion protection include galvanizing, spraying aluminium and zinc, electrophoresis, etc.