What are steel structure anticorrosion methods?

(1) Weathering steel:

    The steels with better corrosion resistance than the normal structural steels are called weathering steel, usually containing phosphorus, copper, nickel, chromium, titanium and other metals, which will form a protective layer on the metal surface to improve corrosion resistance. The low-temperature impact toughness of weathering steel is better than the normal structural steel as well. The standard should meet the "weathering steel welded structure" (GB4172-84).

(2) Hot dip galvanizing:

     Hot dip galvanized steel is a kind of steel after being immersed in rust about 600 ℃ melting zinc solution, so there will be a coating of zinc attached to the steel components’ surface, and the thickness of zinc coating can’t be less than 65μm, in order to play the purpose of anti-corrosion. The advantage of this approach is that can be durable and the quality will be guaranteed. So they have been used a lot in the outdoor steel structures which are corroded seriously and difficult to do atmospheric corrosion maintenance, such as large transmission towers, communication towers and so on.

(3) Thermal spray aluminum (Zn) composite coating:

    This is a long-term effect of anti-corrosion method like hot-dip zinc corrosion. You should first do the sand-blasting for steel components on the surface, to expose the metallic luster. Then using acetylene - oxygen flame to make aluminum (zinc) wire melt, and blowing them with compressed air attached to the steel member surface to form a honeycomb of aluminum (zinc) coating layer (thickness of about 80μm ~ 100μm). Finally, filling the pores with epoxy paint and other coatings or neoprene, to form a composite coating. The advantage of this process is that the adaptability of the components’ size and shape are almost unlimited.

(4) Coating method:

    The anti-corrosive coating method is generally not as good as long-term corrosion protection method (but the lives of fluorocarbon anti-corrosion coating can even up to 50 years). So this uses most for indoor steel structures or the outdoor steel structures which are easy to maintain. The first step of the coating method construction is to remove the rust. The quality of the coating depends on removing rust. So it is usually demanded that the high-quality coating should use blasting abrasive blasting, exposing metallic luster, to remove all rust and oil. The coatings usually need to be done for 4~5 times. The total dry film thickness of the outdoor works are 150μm, while the interior works are 125μm, and the tolerances can be allowed between 25μm. At the beach or at sea, or in a strong corrosive atmosphere, the total dry film thickness can be thickened to 200 ~ 220μm.

(5) Cathodic protection method:

    It is a method that attaching the more reactive metal on the steel structure surface to replace corrosion, which is used in underwater or underground structures mostly.