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Corrosion prevention measures for steel structures
Time：2018-05-15 12:39 Click：
Corrosion prevention measures for steel structures
(1) weathering steel: corrosion resistance is better than the general structure of steel, called "weathering steel", generally contains phosphorus, copper, nickel, chromium, titanium and other metals, so that the metal surface forming protective layer, to improve corrosion resistance. Its low temperature impact toughness is better than that of general structural steel. Standard for weather resistant steel for welded structures (GB4172-84).
(2): the liquid zinc hot dip galvanized hot-dip galvanized steel rust after immersed in 600 DEG C melting, the steel member is attached to the surface of the zinc coating, zinc layer thickness on the 5mm plate shall not be less than 65 m, the thickness of less than 86 M. So as to prevent corrosion purposes. The advantages of this method are long endurance, high production industrialization and stable quality. Thus, the utility model is widely used in outdoor steel structures which are seriously corroded and difficult to be repaired. Such as a large number of transmission towers, communications towers and so on. In recent years, a large number of light steel structural systems such as profiled steel plate. More also use hot-dip zinc corrosion resistance. First process of hot dip galvanizing is pickling, then cleaning. These two processes are not complete, will be hidden corrosion prevention. So it must be dealt with thoroughly. For steel structural designers, it is necessary to avoid the design of a component with a joint surface so as to avoid incomplete pickling or acid washing in the gap of the joint surface. Cause galvanized surface flow yellow water phenomenon. Hot dip galvanizing is done at high temperature. For tubular members, both ends should be open. If the two ends are closed, the air in the pipe is inflated and the head plate is burst, thereby causing a safety accident. If one end is closed, the zinc liquid is not free and easy to store in the pipe.
(3) thermal spraying aluminum (zinc) composite coating: This is a long-term corrosion protection method and corrosion protection effect of quite hot galvanizing. The concrete method is to make sand blasting and rust removing on the surface of the steel structure so as to expose the surface of the metal. Acetylene and oxygen flame are used to melt the continuous aluminum (zinc) wire and blow it to the surface of the steel member with compressed air to form a cellular aluminum (zinc) spraying layer (thickness about 80 m~100 m). Finally, the pores are filled with epoxy or neoprene paint to form a composite coating. The method can not be applied to the inner wall of the tubular member so that the two ends of the tubular member must be hermetically closed so that the inner wall does not corrode. The advantage of this process is that it is adaptable to the size of the component, and the shape and size of the component are almost unlimited. The ship locks, such as Gezhouba Dam, were also constructed in this way. Another advantage is that the thermal effects of the process are local and restrained, resulting in no thermal deformation. With the hot galvanizing of this method compared to the degree of industrialization is low, sandblasting spray aluminum (zinc) with high labor intensity, quality is also susceptible to emotional changes of the effects of the operator.
(4) coating method: coating method is generally better than long-term anti-corrosion anti-corrosion method (but at present, fluorocarbon coating anti-corrosion even up to 50 years). So there are more outdoor steel structures for indoor steel structures or relatively easy to maintain. It costs less at one time, but has higher maintenance costs for outdoor use. The first step in the construction of the coating method is rust removal. Premium coatings depend on thorough rust removal. Therefore, the high coating generally use sand blasting, shot blasting, rust, exposing the luster of the metal, remove all rust and oil. Field construction of the coating can be removed by hand. The choice of coating shall take into consideration the surrounding environment. Different coatings have different tolerance to different corrosion conditions. Coatings usually consist of primers (layers) and finishes (layers). Primers contain lots of powder and less base. The film is rough and has good adhesion with steel, and it has good adhesion to the finish coat. Topcoat is based on many materials, film luster, protective primer, free from atmospheric corrosion, and resistance to weathering. Compatibility between different coatings, and before and after the choice of different coatings should pay attention to their compatibility. The construction of the coating shall be of proper temperature (between 5~38 degrees C) and humidity (relative humidity not greater than 85%). Coating construction environment, less dust, the surface of components can not be condensation. No rain should be allowed within 4 hours after painting. Coatings are usually done over 4~5 times. The total thickness of the dry paint film is 150 m outside the room, and the indoor engineering is 125 m, and the allowable deviation is 25 mu m. At the sea or at sea or in a highly corrosive atmosphere, the total thickness of the dry paint film can be thickened to 200~220 M.
(5) cathodic protection: adding more active metal to the surface of steel structure to replace the corrosion of steel. Often used in underwater or underground structures.