Large steel structures are an important part of a large amount of infrastructure. Bridges, power stations, oil and water pipelines, oil and gas storage tanks, large production devices, ships, offshore structures, towers and many large buildings are widely used in steel structures. Although the carbon steel and some low alloy steel have good mechanical properties and reasonable price, they have serious electrochemical corrosion problems. Due to the characteristics of large dosage and long life requirements, the anti-corrosion means required are also special. Among various corrosion control methods, different surface treatments and anti-corrosion coatings are mainly used to protect large steel structures. So far, it should be said that in most cases, the protective effect is far from ideal, mainly due to the existence of chemical and mechanical failure caused by the life of the coating. Therefore, it is an important task to develop surface modification technology and anti-corrosion products with high performance, long life and meeting the requirements of environmental protection under the new situation. To solve such problems, it is inseparable from high technology and new ideas and adoption.

At present, the application of nanotechnology in steel structure heavy-duty anti-corrosion products is still in its infancy. The application of rare type products at home and abroad is reported. But it is widely believed that the adoption of nanotechnology will undoubtedly bring great gains to the field. The reason is very simple, because the nature of the surface materials and self-protection corrosion products involved in the protection is mainly determined by their microstructure, which involves interface problems, changes in electrochemical history, transmission behavior, changes in the strength and plasticity of surface materials, etc. For example, the introduction of certain types of nanoparticles into organic coatings can increase their resistance to gall, and the plasticity of inorganic coatings can be improved due to the nanosizing of their structure.

Main Technology and Characteristics of Large Steel Structure Anticorrosion

Due to the complexity and diversification of corrosion systems, corrosion control methods are diversified. The most used anti-corrosion technology in industry can be roughly divided into the following points:

(1) reasonable material selection: according to the medium and use conditions, select the appropriate material;

(2) Cathodic protection: the use of electrochemical principle, the components of the additional cathodic polarization to slow down corrosion;

(3) Anodic protection: the passivated system uses an impressed anodic current to blunt the surface of the component to slow down corrosion;

(4) Medium treatment: remove harmful components that promote corrosion, adjust PH value, etc;

(5) Add corrosion inhibitor: add a small amount of material to the medium to slow down the corrosion;

(6) metal surface coating: spray, lining, infiltration, plating, coated with a layer of corrosion-resistant metal or non-metallic (organic or inorganic) substances and metal phosphating, oxidation treatment, in order to reduce the corrosion rate of components;

(7) Anti-corrosion design and improvement of production process.

For a specific corrosion system, should be based on corrosion causes, effects, construction difficulty and economic benefits such as comprehensive consideration. For large steel structures, the solutions that can be used are also diverse. However, in view of their use characteristics, the main use of material selection control and surface coverage for protection, and sometimes often combined with cathodic protection. Taking anti-corrosion coatings as an example, the annual dosage in China may have reached about 200000 tons, accounting for about 10% of the total amount of coatings, and they have a wide variety and different functions.

Nanotechnology in corrosion protection of large steel structures

Nanotechnology has a wide range of applications in various surface modification layers and coatings for different purposes. Only the special requirements for corrosion control of steel structures are discussed here.

(1) the main structure of inorganic coating nano: in the case of inorganic anti-corrosion coating or surface treatment layer, the use of some special methods, can make the coating layer present nano structure, resulting in a series of changes in the properties of the film layer. In general, the covering layer is always chemically inert with respect to the steel substrate. If you want to achieve good anti-corrosion effect and long-term failure, it is required to have high bonding strength with the matrix, complete coverage, less porosity and defects, good uniformity, impact resistance, high strength and certain toughness. Among them, toughness and certain deformation ability are important. In many cases, the main reason for the failure of inorganic coatings is their poor toughness. And of course the total amount of binding. The nanostructure will undoubtedly improve the strength of the inorganic coating, thereby enhancing its resistance to failure. Due to the increase of deformation coordination, it will also improve the bonding strength with the steel surface. It should also be noted that the general anti-corrosion of the coating depends on its effect on the transmission of the medium and the interface bonding, sometimes through the addition of suitable components, it can also have passivation and cathodic protection. Layering nanocrystallization also inevitably has beneficial or unbeneficial effects on these effects.

(2) the performance of traditional organic coatings: by adding some kinds of nano-particles to the coating to form a nano-composite coating, can lead to a substantial improvement in performance. Such as TiO2, SiO2, ZnO, Fe2O3 and other nanoparticles through the scattering of ultraviolet light, can improve the aging resistance of organic coatings. In addition, it can also be used to improve the rheology, adhesion, mechanical strength, hardness, smoothness, light resistance and weather resistance of some kinds of coatings. The role of nanoparticles in these aspects is essentially no different for steel structure anticorrosive coatings and coatings for other uses. There is relatively more work in this area, but there is still a way to go before it is effectively applied in heavy anti-corrosion.

(3) Steel structure self-protection corrosion product form control: weathering steel has better atmospheric corrosion resistance than carbon steel, and generally has corrosion resistance without surface treatment, so it is widely used. The reason is that the corrosion products formed on the surface hinder the entry of the corrosive medium, thereby protecting the substrate. But it also has the problem of corrosion failure. In recent years, it has been found that more dense corrosion product layer can be obtained by surface repentance treatment, so that the corrosion resistance can be greatly improved. The results show that the product has a nano structure. The key here is how to effectively control the morphology of corrosion products artificially.