In the flue system of power plant, metallurgy, chemical industry and other industries, the expansion joint skin, as the core component of non-metallic compensator, has been in the high temperature flue gas environment for a long time. Its fire-proof performance is directly related to equipment safety and personal safety. So, is the flue expansion joint skin fireproof? The answer is yes-the flue expansion joint skin produced by regular manufacturers has excellent flame retardant performance, and some products can reach Class A fire protection standard. This paper will systematically analyze the fire resistance grade, flame retardant mechanism and selection points of skin materials.
1. Flame retardant properties of skin materials
Is the flue expansion joint skin fireproof depends on the composition of its composite material. The skin of non-metallic expansion joint is mainly made of multi-layer soft composite materials, which has many advantages such as wide temperature resistance range, high pressure resistance, strong corrosion resistance, good flame retardancy, sound absorption and shock absorption, good flexibility, etc。
1.1 Fire resistance of base fabric material
The main substrate of the skin is glass fiber cloth, and glass fiber itself is a non-combustible material. The fiberglass cloth maintains good fire resistance after being coated with silicone rubber or fluororubber. The flame retardant grade of silicone cloth material can reach fire resistance grade A, which meets the requirements of GB8624-2006 and German DIN4102 A1。 Glass fiber cloth is used as a base cloth to produce silicone gel cloth by coating or calendering. It is a high-performance and versatile composite material that can be used for a long time between low temperature-70℃ and high temperature 230℃。
1.2 Combustion performance of silicone rubber coating
The fiberglass cloth coated with high temperature curing silicone rubber has the following behaviors after combustion: smokeless, odorless, quick extinguishing, ash whitening, and longer service life。 This feature makes the skin not burn continuously when encountered with open flame, and has self-extinguishing ability.
1.3 Fire protection requirements in actual procurement
Judging from the actual procurement technical specifications, the power plant has clear requirements for the fire resistance performance of the skin. It is clearly stipulated in the procurement technical conditions of a large power group that the fire retardant grade of the expansion joint skin should reach UL94-V0 (the highest grade)。 This grade requires the material to self-extinguish within 10 seconds of leaving the fire in a vertical combustion test without combustion drips.
2. Multi-layer structure and fire protection design of skin
The answer to whether the flue expansion joint skin is fireproof also depends on the design of its multilayer composite structure. A typical skin consists of the following functional layers:
| Structural layer | Commonly used materials | Fire Prevention Contribution |
|---|---|---|
| Outer/Sealing Layer | Silicone/fluororubber coated fiberglass cloth | Surface flame retardant, self-extinguishing off fire |
| Reinforcement layer | Alkali-free glass fiber cloth | Non-combustible substrate, structural support |
| Thermal insulation | Ceramic Fiber Blanket/Aluminum Silicate Needle Felt | Heat insulation and fire prevention, blocking heat conduction |
| Inner anti-corrosion layer | Fluororubber/PTFE film | Chemical corrosion resistance and excellent flame retardancy |
Taking the non-metallic expansion joint of the rear flue of a power plant as an example, its skin adopts 8-layer composite structure, which clearly requires flame retardant, high temperature resistance of 200℃, acid corrosion resistance and good seal。 The fireproof and flame retardant grade of zirconium-containing aluminum silicate needle blanket also reaches UL94-V0 standard。
2.1 Special configuration for high temperature operating conditions
For high-temperature flues with temperatures exceeding 400℃, silicone rubber coating alone is no longer enough to guarantee long-term fire safety. At this time, it is necessary to set a heat insulation layer inside the expansion joint, and use high-temperature composite materials such as fluororubber cloth, polytetrafluoroethylene membrane, glass fiber cloth and ceramic fiber cloth in combination to achieve high-temperature resistance, aging prevention and heat insulation。 The ceramic fiber material can withstand high temperatures above 800℃ and is completely non-flammable。
| Temperature range | Recommended configuration | Fire protection characteristics |
|---|---|---|
| ≤250℃ | Silicone rubber coated fiberglass cloth + fiberglass cloth | Flame retardant surface, economical and applicable |
| 250~400℃ | Fluorine rubber cloth + multi-layer glass fiber cloth + stainless steel wire mesh | High temperature resistance and high flame retardant grade |
| >400℃ | Fluorine rubber + ceramic fiber cloth + zirconium-containing thermal insulation cotton | Non-flammable structure, ultra-high temperature protection |
3. Comparison of fire resistance performance of different types of skins
When answering whether the skin of the flue expansion joint is fireproof, you need to distinguish between different materials:
3.1 Silicone rubber skin
- The long-term working temperature is ≤250℃, and it can reach 350℃ in a short time
- Flame retardant grade up to Class A, self-extinguishing off fire
- Good economy, suitable for conventional flue
3.2 Fluororubber Skin
- Temperature resistance 200~300℃, better corrosion resistance than silicone rubber
- Also have excellent flame retardant properties
- Especially suitable for corrosive environment such as desulfurization system
3.3 Composite high temperature resistant skin
- Contains ceramic fiber layer, and the fire resistance temperature can reach 800~1200℃
- Optimum fireproof performance, suitable for high temperature sections such as boiler outlet
- When the flue gas temperature is 1000℃, the outer skin can still work normally
4. Practical significance of skin fire prevention
Whether the skin of flue expansion joint is fireproof is not only a problem of product performance, but also related to:
4.1 Preventing the spread of fire
In the case of a fire in the flue system of power plants and chemical plants (such as carbon deposit combustion and combustible gas deflagration), the non-flammable or flame-retardant skin can effectively prevent the fire from spreading along the flue and buy time for emergency response.
4.2 Eliminate the risk of combustion drip
The UL94-V0 rating requires the material to burn without dripping. Ordinary plastic materials will drip molten matter when burning, which may ignite the equipment below or cause people to burn. However, the silicone rubber/fluororubber composite material is carbonized and does not drip during combustion, which is more safe。
4.3 Meet fire acceptance requirements
The fire protection acceptance of industrial buildings has clear provisions on the fire protection grade of pipeline insulation and sealing materials. The selection of flame-retardant skin is a necessary condition for enterprises to pass fire inspection.
V. Suggestions on selection and use
In order to ensure that the flue expansion joint skin is fireproof to get a positive answer, attention should be paid to the following in the selection and use:
5.1 Confirmation points when purchasing
- Verify that the temperature requirements of the operating condition are met
- View product structure layers and material description
5.2 Installation Precautions
- The skin surface coating shall not be damaged during installation
- When welding the end pipe, cover the skin with asbestos cloth to prevent burning by welding slag
- Ensure that the guide tube is installed correctly to avoid high-temperature smoke directly washing the inner layer of the skin
5.3 Operation and Maintenance
- Check the skin surface regularly for any signs of carbonization, cracking and burning
- If the flame retardant coating is found to be aging and falling off, it should be replaced in time
- Over-temperature operation will accelerate material aging, smoke temperature should be strictly controlled
VI. SUMMARY
Is the skin of flue expansion joint fireproof-regular products have excellent flame retardant properties. The core conclusions are as follows:
- Material is the key: silicone rubber/fluororubber coated glass fiber cloth as the base material, glass fiber is non-flammable, the coating layer is self-extinguishing off fire
- High temperature requires composite structure: working conditions above 400℃ need to be equipped with non-combustible insulation layer such as ceramic fiber, and the fire resistance temperature can reach 800-1200℃
- Required inspection report for procurement: Suppliers shall be required to provide fire rating inspection report during model selection to ensure that products meet fire protection specifications
Therefore, as long as you choose the products produced by regular manufacturers and meet the relevant fire protection standards, the flue expansion joint skin has reliable fire protection performance. However, it should be noted that long-term overtemperature operation will accelerate the aging of materials, resulting in the decline of flame retardant performance. In daily operation, the flue gas temperature should be strictly controlled within the allowable range of the skin, and the aging products should be regularly inspected and replaced.