Municipal public facilities, such as large exhibition centers, sports venues, airport terminals, TV towers, bridges, etc., all use a large amount of steel, with steel structures being the main structural form. Steel is an important structural material in modern architecture, with high strength, stable performance, good toughness, easy processing and production, suitable for mass production, and easy to control quality and install quickly. Therefore, it is particularly suitable for constructing large-span, super tall, and super heavy buildings.
The exhaust emissions from automobiles, sulfur-containing flue gas emissions from power plants and boiler chimneys in general urban environments; Industrial air pollution in industrial cities and salt spray erosion in coastal cities; The humid and hot conditions in southern cities will inevitably lead to corrosion of steel structures. The use of anti-corrosion coatings for the coating protection of steel structures in municipal public facility buildings is an economically feasible method, and an appropriate coating system can achieve durability of over 25 years.
As a building steel structure, in addition to considering anti-corrosion, another key factor to consider is coating fire prevention, because the fire resistance performance of building steel structures is poor, mainly reflected in two aspects: first, the thermal conductivity coefficient of steel is very high, and steel components heat up quickly under fire; The second reason is that the strength of steel decreases rapidly with increasing temperature, causing the steel structure to collapse due to the inability to withstand external surface loads. The main purpose of fire prevention in building steel structures is to provide sufficient escape time in the event of a fire. Therefore, in order to prevent and reduce the fire hazards of building steel structures, it is necessary to carry out scientific fire protection design for steel structures and adopt safe, reliable, and economically reasonable fire protection measures.
The application of anti-corrosion and fireproof coatings in steel structures of municipal public facilities not only needs to consider long-term durability and aesthetic decoration, but also environmental protection. The heavy-duty anti-corrosion and fireproof coatings used for building steel structures should reflect the best combination of performance, aesthetics, and environmental regulations
The corrosive media faced by steel structure buildings mainly include:
1. Moisture in the atmosphere: In urban environments with high humidity, especially near rivers, lakes, or beaches, water in the air can form a water film on the surface of steel structures, accelerating the corrosion process
2. Oxygen in the atmosphere: Oxygen is a key factor in the oxidation reaction of steel, which combines with the moisture on the surface of the steel to form a corrosive electrolyte
3. Air pollution: Industrial emissions and automobile exhaust in cities contain acidic gases such as sulfur dioxide (SO2) and nitrogen oxides (NOx), which dissolve and exacerbate the corrosion of steel structures
4. Dust and particulate matter: Dust and particulate matter in cities can adsorb onto the surface of steel structures, and these substances may contain corrosive components that accelerate the corrosion process.
5. Salt content: Steel structures in coastal cities are also affected by salt spray, and salt in seawater (mainly sodium chloride NaCl) has strong corrosiveness, which can accelerate the corrosion rate of metals
6. Microorganisms: In humid environments, microorganisms such as bacteria, fungi, etc. may also participate in the corrosion process, especially in warm and humid climatic conditions
7. Chemical substances: Certain chemicals in cities, such as cleaning agents, antifreeze, etc., may also come into contact with steel structures, and the components in these chemicals can promote corrosion
8. Temperature changes: Temperature differences in cities can also affect steel structures, especially in situations where there is a large temperature difference between day and night. Temperature changes can cause condensation on the surface of steel structures, thereby accelerating corrosion
9. Industrial emissions: Steel structures in industrial areas are also affected by specific industrial emissions, such as acidic gases, heavy metal ions, etc
In order to cope with the impact of these corrosive media, urban steel structure buildings usually need to take effective anti-corrosion measures, such as coating high-performance coatings, adopting cathodic protection systems, using corrosion-resistant alloys, etc., to ensure the durability and safety of the structure
Current national standards and regulations, mandatory standard provisions, etc
Code for Construction and Acceptance of Building Anti corrosion Engineering (GB50212-2002)
GB8923-1988 "Standard for Corrosion and Derusting Grades of Steel Surfaces before Coating"
Safety Regulations and Safety Management Rules for Painting Operations (GB6514-1995)
Quality Requirements for Anti corrosion Coatings (GB6514-1991)
Safety Regulations for Paint Operations, Paint Process Safety, and Ventilation Purification (DJ/T6931-1999)
Code for Construction and Acceptance of Industrial Equipment and Pipeline Anti corrosion Engineering (HGJ229-91)
Safety Regulations for Painting Operations - Safety of Pre treatment Processes for Painting (GB7692-87)
Noise Limits for Construction Sites (GB12523-90)
ISO9001 Quality Management System Documents
ISO14001 Environmental Management System Document
GB/T28001 Occupational Health and Safety Management System Documents
The anti-corrosion coating specifications for steel structures are mainly formulated according to ISO12944. ISO12944 is currently a globally recognized authoritative standard compiled by the International Organization for Standardization for owners, designers, consultants, coating contractors, coating production enterprises, and other professionals engaged in coating anti-corrosion work. It provides important references for these personnel, units, and organizations.
ISO12944 comprehensively introduces all requirements for protective coating of steel structures, including design life, corrosion environment, structural design, surface treatment, coating system, coating product performance, construction supervision, and the development of new construction and maintenance supporting plans. When designing anti-corrosion coating systems for steel structures, ISO12944's approach to developing coating systems mainly includes the following aspects.
Analyze the corrosion environment of steel structures and determine their corrosion level (ISO12944-2)
Determine the expected protection period for steel structures (ISO12944-5)
Determine the operating conditions of steel structures, such as temperature, humidity, medium, indoor, and outdoor
Understand the regulations and requirements of national standards related to anti-corrosion coating of building steel structures
Select the coating variety and film thickness based on the best cost-effectiveness, and determine the coating matching system
The Corrosion environment defined in ISO12944-2 is a guide for developing protective coatings. Most of the steel structures used in public facilities, such as sports arenas and convention centers, are located in environments ranging from C2 to C4. Metallurgical and petrochemical enterprises, as well as marine engineering steel structures, are typically exposed to highly corrosive C5 environments. Corrosion environment and status listed in ISO12944-2 (Refer to Table 3-3-93), it cannot cover all situations. Therefore, designers should design coating schemes based on their own research and experience, with targeted approaches
Environmental conditions: The corrosion level of atmospheric environment on building steel structures under long-term action can be determined according to Table 1
| Classification of Atmospheric Corrosivity and Typical Environmental Cases | ||||||
|---|---|---|---|---|---|---|
| Corrosivity level | Loss of mass and thickness per unit area（After the first year of exposure） | Typical environmental cases under warm climate conditions（For reference only） | ||||
| Bottom carbon steel | zinc | outer surface | interior surface | |||
| Mass loss | Thickness loss | Mass loss | Thickness loss | |||
| /g·m2 | /um | /g·m2 | /um | |||
| C1Low content | ≤10 | ≤1.3 | ≤0.7 | ≤0.1 | / | Heated interior of buildings with clean air, such as offices, shops, schools, and hotels |
| C2 Low content | ＞100-200 | ＞1.3-25 | ＞0.7-5 | ＞0.1-0.7 | Low pollution level atmosphere, mostly in rural areas | Unheated buildings where condensation may occur (such as warehouses, gyms, etc.) |
| C3 Moderate contentderate content | ＞200-300 | ＞25-50 | ＞5-15 | ＞0.7-2.1 | Urban and industrial atmospheres, moderate sulfur dioxide pollution, and low salinity coastal areas | In production plants with high temperatures and some air pollution, such as food processing plants, laundry plants, distilleries, dairy factories, etc |
| C4 High content | ＞400-650 | ＞50-80 | ＞15-30 | ＞2.1-4.2 | Chemical plants, swimming pools, coastal ships, shipyards, etc moderate salinity | Chemical plants, swimming pools, coastal ships, shipyards, etc |
| C5 High | ＞650-1500 | ＞80-200 | ＞30-60 | ＞4.2-8.4 | Industrial areas with high humidity and severe weather, and coastal areas with high salinity | Buildings and areas where condensation and high pollution continue to occur and exist |
| CX Extreme | ＞1500-5500 | ＞200-700 | ＞60-180 | ＞8.4-25 | Marine areas with high salinity and tropical subtropical industrial areas with extremely high humidity and aggressive atmosphere | Industrial areas with extremely high humidity and corrosive atmosphere |
| Note: The loss value used to define the corrosiveness level is the same as that given in ISO9223. | ||||||
ISO 12944-1 (2017) divides the design service life of anti-corrosion coating systems into four levels. The design life of steel structure protection refers to the service life of the coating system before the first major overhaul. Before the first major overhaul, it refers to the coating corrosion area reaching Ri3 level of IS04628.3 standard, with a corrosion area of 1% (equivalent to ASTM) D610 level 6), and at this time, the maintenance effect is the best and the most economical. It should be noted that the design life of the coating system is not a guarantee time. Its design life is different from the actual service life. The design life is considered to be the coating system service life when the coating quality, steel structure design, surface treatment, construction standards, construction conditions, coating construction, etc. are fully qualified or meet the requirements, and the exposed corrosion environment after completion is relatively stable. In addition, regular inspections and partial repairs of the coating are essential maintenance work before major repairs. Steel structure buildings require high durability, so for coating systems, high durability is also required. So for the coating design of steel structure buildings, it is a heavy-duty anti-corrosion coating system that has been in use for more than 15 years, or even more than 25 years
In ISO 12944-5, important definitions are provided for the use of existing coatings and coating systems. ISO Tables C.1-C.6 in Appendix C provide examples of primer, intermediate coat, and topcoat coatings used in combination with different binders, anti rust pigments, and dry film thicknesses for carbon steel. Select a rough protective coating system based on the corrosion factors identified in 1S012944.2, and list the protective coating systems that have been proven to be suitable for different corrosion environments and levels.
The application of graphene coatings in steel structure buildings demonstrates its unique advantages: the unique two-dimensional structure of graphene endows the coating with excellent shielding performance, which can effectively prevent moisture, oxygen, and corrosive substances from penetrating the surface of the steel structure, significantly improving the anti-corrosion effect. At the same time, the addition of graphene significantly enhances the mechanical properties of the coating, improves the impact resistance and wear resistance of the coating, and makes the coating more durable. Graphene coating is easy to apply and can quickly form a uniform coating, suitable for various complex steel structure surfaces, simplifying the construction process. In addition, graphene coatings do not contain volatile organic compounds (VOCs), reducing their impact on the environment and meeting the requirements of green buildings. Due to the stability and weather resistance of graphene, graphene coatings can provide longer lasting protection, reducing maintenance frequency and costs. In summary, graphene coatings provide an efficient, durable, and environmentally friendly anti-corrosion solution for steel structure buildings, significantly enhancing their durability and safety.
| Design basis | ISO12944-5：2017 Corrosion Protection of Steel Structures by Paint and Varnish Protective Paint Systems |
| Current environment | C3 moderate; External factors: urban and industrial atmosphere, moderate sulfur dioxide pollution, and low salinity coastal areas |
| Design Life | Mid term M |
| Surface Treatment | ISO 8501-1 Sa2.5：Thoroughly spray or eject rust removal. There is no visible grease, dirt, oxide scale, rust, paint coating or other attachments on the surface of the steel, and any residual traces are only slight color spots in dots or strips. |
| Thoroughly spray rust removal to Sa2.5 level (ISO) 8501-1:2007), when observed without magnification, the surface should be free of visible oil, grease, and dirt, and there should be no oxide scale, rust, coating, or foreign impurities. Any residual traces of pollutants should only appear as slight color spots in the form of dots or stripes. Painting area | Steel structure building, high-speed rail, airport |
| coating | Type of coating | Paint name | Color | Supporting diluent | A: B supporting facilities | Film thicknessμm |
|---|---|---|---|---|---|---|
| Step 1 | KnkaZinc | Graphene zinc foundation make-up KnkaZinc 30 Gns | Graphite grey | Graphene specific thinner KnkaThinner 17 Gns | 30.8:3.2 | 40 |
| Step 2 | KnkaCover | Graphene low surface treatment primer KnkaCover 220 Gns | Gray, light gray, reddish brown, white medium light | Graphene specific thinner KnkaThinner 17 Gns | 25:5 | 120 |
| Step 3 | KnkaDur | Acrylic acid Hardtop AS KnkaDur 550 | Support Ra·l and GB color matching. | Polyurethane diluent KnkaThinner 10 | 21.4:3.6 | 40 |
| Amount to | 200 | |||||
Cold spray zinc technology has brought many advantages to steel structure construction: it not only provides excellent anti-corrosion performance, but also effectively prevents steel structures from being corroded by atmosphere, water or chemicals; And the construction is convenient and efficient, without the need to heat the metal substrate, it can be directly sprayed on site, suitable for already installed steel structures, reducing the cost of disassembly and handling; The coating is uniform and delicate, forming a good coverage even in complex geometric shapes and small gaps, ensuring anti-corrosion effect; Cold spray galvanizing has extremely high adhesion with metal substrates, is not easy to peel off, and can maintain stability in various environments; The coating dries almost immediately and can be quickly put into use or processed, improving construction efficiency; If the coating is locally damaged, it can be repaired through local repair, reducing maintenance costs; There are no harmful gas emissions during the construction process, which has a relatively small impact on the environment and meets the requirements of green buildings. In summary, Cold spray zinc technology provides an efficient, convenient, and environmentally friendly anti-corrosion solution for steel structure buildings.
| Design basis | ISO12944-5：2017 Corrosion Protection of Steel Structures by Paint and Varnish Protective Paint Systems |
| Current environment | C3 moderate; External factors: urban and industrial atmosphere, moderate sulfur dioxide pollution, and low salinity coastal areas |
| Design Life | Mid term M |
| Surface Treatment | ISO 8501-1 Sa2.5：Thoroughly spray or eject rust removal. There is no visible grease, dirt, oxide scale, rust, paint coating or other attachments on the surface of the steel, and any residual traces are only slight color spots in dots or strips. |
| Thoroughly spray rust removal to Sa2.5 level (ISO) 8501-1:2007), when observed without magnification, the surface should be free of visible oil, grease, and dirt, and there should be no oxide scale, rust, coating, or foreign impurities. Any residual traces of pollutants should only appear as slight color spots in the form of dots or stripes. Painting area | Steel structure building, high-speed rail, airport |
| coating | Type of coating | Paint name | Color | Supporting diluent | A: B supporting facilities | Film thickness |
|---|---|---|---|---|---|---|
| Step 1 | KnkaZinc | Cold spray zinc KnkaZinc 96 | Zinc Grey | thinner KnkaThinner 16 AX | 30:0 | 60 |
| Step 2 | KnkaCover | Cold spray zinc sealer KnkaCover 167 | Gray, no light | Epoxy diluent KnkaThinner 17 | 27:4.5 | 100 |
| Step 3 | KnkaDur | Acrylic acid Hardtop AS KnkaDur 550 | Support Ra·l and GB color matching. | Polyurethane diluent KnkaThinner 10 | 21.4:3.6 | 40 |
| Amount to | 200 | |||||
Steel structure buildings have the following advantages: short construction period, good seismic performance, high safety, large prefabrication and design flexibility, suitable for different climate conditions and atmospheric environments. In addition, steel structure construction has low pollution, low noise, and no dust pollution, making it a green and environmentally friendly building. So in the late 1990s, a large number of advanced design theories and ideas, as well as technologies in processing, manufacturing, and installation, were introduced from abroad in China, which led to the rapid development of domestic steel structure buildings, especially in recent years. The use of steel structures in some super high-rise buildings, industrial plant buildings, bridge buildings, elevated overpasses, sports and cultural venues, tower buildings, etc. is becoming increasingly common. However, the widespread application of steel structures has also exposed a series of problems throughout the entire store, and the more serious one is the corrosion of steel structures.
| Design basis | ISO12944-5：2017 Corrosion Protection of Steel Structures by Paint and Varnish Protective Paint Systems |
| Current environment | C3 moderate; External factors: urban and industrial atmosphere, moderate sulfur dioxide pollution, and low salinity coastal areas |
| Design Life | Mid term M |
| Surface Treatment | ISO 8501-1 Sa2.5：Thoroughly spray or eject rust removal. There is no visible grease, dirt, oxide scale, rust, paint coating or other attachments on the surface of the steel, and any residual traces are only slight color spots in dots or strips. |
| Thoroughly spray rust removal to Sa2.5 level (ISO) 8501-1:2007), when observed without magnification, the surface should be free of visible oil, grease, and dirt, and there should be no oxide scale, rust, coating, or foreign impurities. Any residual traces of pollutants should only appear as slight color spots in the form of dots or stripes. Painting area | Column, beam, truss, frame structure |
| coating | Type of coating | Paint name | Color | Supporting diluent | A: B supporting facilities | Film thicknessμm |
|---|---|---|---|---|---|---|
| Step 1 | KnkaZinc | Epoxy Rich Zinc Primer KnkaZinc 80 | zinc grey | Epoxy diluent KnkaThinner 17 | 30:3 | 40 |
| Step 2 | KnkaCover | Epoxy micaceous iron intermediate paint KnkaCover 150 | Light gray mica iron oxide | Epoxy diluent KnkaThinner 17 | 25.2:6.8 | 80 |
| Step 3 | KnkaDur | Acrylic acid Hardtop AS KnkaDur 550 | Support Ra·l and GB color matching. | Polyurethane diluent KnkaThinner 10 | 21.4:3.6 | 60 |
| Amount to | 180 | |||||
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