The wide application of steel in the construction field is self-evident. It has the advantages of high strength, plasticity, durability, etc., and is widely used in important structures such as high-rise buildings, bridges, and industrial facilities. However, although steel itself is not flammable, in a high-temperature fire environment, the mechanical properties of steel will rapidly decrease, its bearing capacity and stability will be seriously threatened, and even cause structural collapse. Therefore, the surface of steel needs to be painted with fire retardant paint to ensure additional protection for buildings and facilities in the event of a fire.
This article will explore in depth why steel needs to be painted with fire retardant paint, as well as related issues such as the service life of fire retardant paint.
What is the weakness of steel in fire?
The melting point of steel is about 1500℃, so it seems that steel will not melt easily due to fire. But in fact, the performance of steel will be significantly reduced in a fire, especially when the temperature reaches above 500℃, its strength and stiffness will rapidly weaken. At the beginning of a fire, the steel structure in a building may appear intact, but as the temperature continues to rise, the steel's load-bearing capacity gradually decreases, resulting in a significantly increased risk of collapse of the building or structure.
The key weaknesses of steel in fire are mainly reflected in the following aspects:
1. Temperature sensitivity of steel: Although steel has good durability and strength, its high temperature resistance is poor. When the temperature rises to 300℃, the strength of steel begins to decrease, and when the temperature reaches 500℃ to 600℃, the load-bearing capacity of steel is reduced by about half. Continuous high temperature can cause steel to lose its structural function, causing partial or complete collapse of buildings or facilities.
2. Thermal expansion effect: The high temperature in a fire causes thermal expansion of steel, and the steel structure deforms due to thermal stress, which may cause the entire structure to become unstable or partially fractured. This effect is particularly dangerous in the case of a rapidly spreading fire.
3. Heat transfer of the structure: Steel has good thermal conductivity, which means that flames and high temperatures can be quickly transferred through the steel to other adjacent components, accelerating the spread of the fire and causing more extensive damage.
Therefore, although steel performs well at room temperature, its fragility is exposed in a fire environment. This is why fire retardant paint has become a vital protective measure in the design and construction of steel structures.
What is the mechanism of action of fire retardant paint?
The main function of fire retardant paint is to delay the impact of fire on steel and ensure that the steel structure maintains its bearing capacity and structural stability for a long enough time in a high temperature environment. Fire retardant paint can form a heat-insulating protective layer through physical and chemical reactions, reducing the heat conduction and temperature rise rate on the surface of the steel.
1. Heat-insulating effect
Fire retardant paint can effectively isolate the contact between flames and steel in a fire and delay the direct ablation effect of the flame. In particular, intumescent fire retardant paint will rapidly expand under high temperature to form a dense foam layer or carbonized layer. This protective layer can not only effectively isolate heat, but also prevent steel from contacting oxygen in the air, thereby inhibiting further combustion reactions.
2. Expansion effect
Intumescent fire retardant paint is the most common type of steel structure protection. Its working principle is that when encountering high temperature, the components in the paint will react chemically, the coating will expand rapidly, the volume will increase several times or even dozens of times, and a thick insulation layer will be formed. This carbonized layer can absorb and isolate a large amount of heat, slow down the temperature rise of steel, and buy precious time for personnel evacuation and rescue.
3. Reduce the temperature rise rate of steel
The most critical role of fire retardant paint on the surface of steel is to reduce the temperature rise rate. By controlling the speed at which heat is transferred to steel, the stability of steel structures in fires can be effectively extended. Different types of fire retardant paint have different fire resistance limits, which can generally provide protection time ranging from 30 minutes to 2 hours, ensuring that the steel structure will not fail due to excessive temperature rise in the early stage of the fire.
What are the types of fire retardant paint?
According to their different components and functions, fire retardant paint can be roughly divided into expansion fire retardant paint and non-expansion fire retardant paint.
1. Intumescent fire retardant paint
Intumescent fire retardant paint is one of the most common fire retardant paints for steel structures. In the event of a fire, the coating expands rapidly to form a foamy carbonized insulation layer that isolates the heat source and protects the steel. Its advantage is that the coating is thinner but can provide fire protection for a longer period of time.
2. Non-intumescent fire retardant paint
Non-intumescent fire retardant paint relies mainly on its high temperature tolerance to form a dense insulation layer that slows down the direct damage of the flame to the substrate. Although this type of paint does not expand like intumescent paint, it still has a significant fire retardant effect and is generally suitable for industrial facilities and equipment that do not require high appearance.
What is the service life of fire retardant paint?
The service life of fire retardant paint is affected by many factors, including the type of paint, construction quality, environmental conditions, and subsequent maintenance. Generally speaking, the service life of fire retardant paint can reach 10 to 20 years, but the specific time depends on the following key factors:
1. Environmental factors
The environment in which the steel structure is located has a direct impact on the service life of fire retardant paint. If the steel is exposed to moisture, corrosive gases or acid-base environments, the protective effect of fire retardant paint may be greatly shortened. Humid air may cause chemical changes in the composition of fire retardant paint, thereby affecting its fire resistance. In a corrosive environment, the durability of fire retardant paint will also be significantly reduced, and regular inspection and repair are required.
2. Maintenance and care
Fire retardant paint needs to be inspected and maintained regularly, especially for steel structures that are exposed to harsh environments for a long time. The effective life of fire retardant paint can be extended through regular surface cleaning and repair. In addition, during use, if the coating is found to be peeling, cracking, etc., it must be repaired in time, otherwise the fire resistance will be greatly reduced.
3. Construction quality
The construction quality of fire retardant paint is also crucial to its service life. During construction, it is necessary to strictly follow the relevant standards and specifications to ensure that the coating has uniform thickness and good adhesion to achieve the best fireproofing effect. If the construction is improper, the coating may not fully exert its fireproofing effect and its service life will be shortened accordingly.
4. Types of coatings
Different types of fire retardant paints have different service lives. Intumescent fire retardant paints have a relatively long service life and strong environmental resistance, while some non-intumescent coatings may have weaker durability in harsh environments. Therefore, when choosing fire retardant paints, it is necessary to comprehensively consider factors such as the fireproofing requirements and environmental conditions of the building.
What are the construction precautions for fire retardant paints?
The construction quality of fire retardant paints directly affects its service life and fireproofing effect. In the actual construction process, the following precautions need to be followed:
1. Surface treatment: Before applying fire retardant paint, the steel surface needs to be strictly cleaned and treated to ensure that there are no impurities such as oil stains, rust spots, and dust to ensure the adhesion and fireproofing effect of the coating.
2. Coating thickness: The thickness of the coating is crucial to the fire retardant performance. During construction, the coating thickness should be uniform and meet the requirements of the design specifications. Generally speaking, the thicker the coating thickness, the better the fire retardant performance.
3. Environmental requirements: The construction environment should be kept dry, and construction should be avoided in humid and rainy weather to prevent the coating from absorbing moisture and causing failure.
4. Preservation and preparation of the paint: Fire retardant paint should be prepared according to the product instructions before use to prevent the paint from failing due to environmental factors during storage.
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