Large steel structures are an important component of a large amount of infrastructure. Bridges, power plants, oil and water pipelines, oil and gas storage tanks, large production facilities, ships, offshore structures, towers, and many large buildings extensively use steel structures. Although the carbon steel used has good mechanical properties and reasonable prices compared to some low-alloy steels, they have serious electrochemical corrosion problems. Due to the large quantity used and the long lifespan requirements, the necessary anti-corrosion measures are also special. Among various corrosion control methods, different surface treatments and the application of anti-corrosion coatings are mainly selected to protect large steel structures. So far, it can be said that in most cases, the protective effect is still far from ideal, mainly due to the lifespan issues of the covering layer caused by chemical and mechanical failures. Therefore, developing high-performance, long-lifespan surface modification technologies and anti-corrosion products that meet environmental protection requirements under new conditions is an important task. Solving such problems relies on high technology, new ideas, and adoption.

Currently, the application of nanotechnology in heavy anti-corrosion products for steel structures is still in its infancy. There are few reports on the application of such products both domestically and internationally. However, it is generally believed that the adoption of nanotechnology will undoubtedly bring significant benefits to this field. The reason is simple: the properties of the surface materials involved in protection and the self-protective corrosion products are mainly determined by their microstructure, which involves interface issues, changes in electrochemical processes, transport behavior, and changes in the strength and plasticity of surface materials, etc. For example, introducing certain types of nanoparticles into organic coatings can increase their resistance to aging, and the plasticity of inorganic coatings can be improved due to the nanostructuring of their structure.

Main technologies and characteristics in the anti-corrosion of large steel structures

Due to the complexity and diversity of corrosion systems, the means of corrosion control have also diversified. The most commonly used anti-corrosion technologies in industry can be roughly divided into the following points:

(1) Reasonable material selection: Choose suitable materials based on the medium and usage conditions;

(2) Cathodic protection: Use electrochemical principles to apply external cathodic polarization to components to slow down corrosion;

(3) Anodic protection: For passivated systems, apply external anodic current to make the surface of components passive to slow down corrosion;

(4) Medium treatment: Remove harmful components that promote corrosion, adjust pH, etc.;

(5) Add inhibitors: Add a small amount of substances to the medium to slow down corrosion;

(6) Metal surface coating: Spray, line, infiltrate, plate, or coat a layer of corrosion-resistant metal or non-metal (organic or inorganic) material, and perform phosphating or oxidation treatment on the metal to reduce the corrosion rate of components;

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

For a specific corrosion system, comprehensive consideration should be given to the causes of corrosion, effects, construction difficulty, and economic benefits, etc. For large steel structures, there are also various schemes that can be adopted. However, based on their usage characteristics, the main protective measures are material selection control and surface coating, which are often used in conjunction with cathodic protection. Taking anti-corrosion coatings as an example, the annual usage in our country may have reached about 200,000 tons, accounting for about 10% of the total amount of coatings, and they come in various types with different functions.

Nanotechnology in the anti-corrosion of large steel structures

Nanotechnology has broad application prospects in various surface modification layers and coatings for different purposes. Here, we will discuss the special requirements for corrosion control of steel structures.

(1) Nanostructuring of the main structure of inorganic coatings: In the case of inorganic anti-corrosion coatings or surface treatment layers, using certain special methods can make the coating present a nanostructure, thereby bringing a series of changes in the properties of the film layer. Generally, the coating is relatively inert in chemical properties compared to the steel substrate. To achieve good anti-corrosion effects and long-lasting effectiveness, it requires high bonding strength with the substrate, complete coverage, low porosity and defects, good uniformity, impact resistance, high strength, and certain toughness. Among these, toughness and a certain ability to deform are important. In many cases, the main reason for the failure of inorganic coatings is their poor toughness. Of course, there is also the total bonding force. Nanostructuring will undoubtedly improve the strength of inorganic coatings, thereby enhancing their resistance to failure. Due to increased deformation coordination, it will also improve the bonding strength with the steel surface. It should also be noted that general coating anti-corrosion relies on its ability to slow down the transport of the medium and the effect of interface bonding. Sometimes, through the addition of suitable components, it can also have passivation and cathodic protection effects. For these effects, layer nanostructuring inevitably brings beneficial or detrimental impacts.

(2) Improvement of the performance of traditional organic coatings: By adding certain types of nanoparticles to the coatings to form nanocomposite coatings, significant improvements in performance can be achieved. For example, nanoparticles such as TiO2, SiO2, ZnO, Fe2O3 can enhance the aging resistance of organic coatings through their scattering effect on ultraviolet light. In addition, they can also improve the rheology, adhesion, mechanical strength, hardness, smoothness, light resistance, and weather resistance of various coatings. The role of nanoparticles in these aspects is essentially no different for anti-corrosion coatings for steel structures and coatings for other purposes. There has been relatively more work in this area, but there is still a long way to go before effective applications in heavy anti-corrosion.

(3) Control of the morphology of self-protective corrosion products of steel structures: Weathering steel has better atmospheric corrosion resistance compared to carbon steel and generally does not require surface treatment to have corrosion resistance, thus it is widely used. The reason is that the corrosion products formed on its surface hinder the entry of corrosive media, thereby protecting the substrate. However, it also has corrosion failure issues. Recent studies have found that through surface treatment, a denser layer of corrosion products can be obtained, significantly improving anti-corrosion performance. Research shows that the resulting products have a nanostructure. The key here is how to effectively control the morphology of corrosion products artificially.