In industrial flue gas treatment system, fabric expansion joint skin is the core and most critical flexible component of non-metallic expansion joint. It is like the "heart" of the expansion joint, which determines the tightness, displacement compensation ability and service life of the whole compensator. Different from metal bellows, fabric expansion joint skin is made of multi-layer high-performance non-metallic materials, which has unique advantages such as large compensation, corrosion resistance and no reverse thrust. So, what is the structure of fabric expansion joint skin? How to select a model? This paper will systematically analyze the technical knowledge of fabric expansion joint skin from the structure composition to the key points of type selection.
First, the definition and core function of fabric expansion joint skin
Fabric expansion joint skin, also known as non-metallic skin and desulfurization ring belt, is a flexible sealing body made of a variety of high-performance non-metallic materials laminated and compounded by special technology. It is the main telescopic body of non-metallic expansion joint, which can absorb the thermal displacement, mechanical displacement and installation error of pipeline system, at the same time isolate vibration and noise, and act as an important barrier to bear the working pressure of system medium.
Compared to traditional metal expansion joints, fabric expansion joint skins have the following significant advantages:
| peculiarity | Specific Description |
|---|---|
| Large amount of compensation | Can absorb three-dimensional displacement up to 30%-40% of the effective length |
| Multidirectional compensation | Can compensate axial, lateral and angular displacements simultaneously |
| No reverse thrust | The main body is fiber fabric, weak transmission, which can simplify the design of the stent |
| Strong corrosion resistance | Fluoroplastics and silicone materials have natural resistance to acid, alkali and smoke |
| Noise and vibration isolation | Fiber fabric and thermal insulation cotton have sound absorption and vibration isolation function |
| Easy maintenance | Local damage can be repaired online without the need for overall replacement |
2. Structure and material composition of fabric expansion joint skin
Fabric expansion joint skin is not a single material, but a typical composite structure. Its classical structure typically comprises the following functional layers from top to bottom (outward from the media side):
| Structural hierarchy | Materials | function |
|---|---|---|
| Sealing/temperature resistant layer (inner layer) | Fluorine rubber (FPM), Silicone rubber (Silicone), PTFE coated fiberglass cloth | Direct contact with media, high temperature resistance, corrosion resistance, aging resistance, ensure no leakage |
| Thermal insulation | Ceramic fiber blanket, glass fiber needle blanket | Blocks heat transfer at high temperatures and protects external structures |
| Structural reinforcement layer | High-strength glass fiber cloth, polyester fiber cloth; Basalt fiber cloth or aramid fiber cloth for special occasions | The "skeleton" of the skin, which bears the positive and negative compressive stresses of the system |
| Stainless steel wire mesh | 304 stainless steel wire mesh | Inner lining protection to prevent debris from entering and prevent insulation material from scattering |
| Outer protective layer (outer layer) | Fiberglass cloth coated with fluororubber or silicone rubber | Protection against external environment (UV rays, rain, wind erosion, mechanical wear) |
According to the actual working conditions, the total thickness of the skin is generally 2-10mm, the tensile strength is ≥15Pa, and the service life can reach more than 10 years under normal working conditions.
3. Material classification and temperature resistance grade of fabric expansion joint skin
Fabric expansion joint skin is mainly divided into two categories according to different core materials: silicone skin and fluorine skin:
1. Silicone skin
The base cloth of silicone skin is glass fiber cloth, which is coated or rolled by silicone rubber. It is suitable for working conditions with temperature resistance ≤600 ℃, has good weather resistance and flexibility, and has high cost performance.
2. Fluorine rubber skin
The fluorine rubber skin uses fluorine rubber (FPM) as the coating material, and the content of fluorine rubber can reach more than 76%. It is suitable for extreme high temperature environment, with temperature resistance up to 1200℃, and excellent acid and alkali resistance and oil resistance.
3. Examples of typical skin composite structures
Taking Class III ring belt (highest grade) as an example, its typical seven-layer structure is:
| Sequence | Materials |
|---|---|
| Level 1 (surface layer) | Silicone rubber glass fiber fabric cloth |
| Level 2 | Industrial canvas |
| Level 3 | Aluminum silicate fiberglass cloth |
| Level 4 | Asbestos cloth |
| Level 5 | Zirconium-containing fiberglass blanket |
| Level 6 | Wire-filled fiberglass cloth |
| Layer 7 (inner layer) | Stainless steel wire mesh |
4. Core Performance Parameters of Fabric Expansion Joint Skin
Understanding and mastering the performance parameters of fabric expansion joint skin is the basis of correct type selection:
| parameter | Typical Value/Range |
|---|---|
| Fabric thickness | 2-10mm |
| Heat-resistant temperature | 50℃-1200℃ (depending on the material) |
| Working pressure | ≤0.3MPa |
| Compensation amount | 50-300mm |
| Three-dimensional displacement compensation | Up to 30%-40% of effective length |
| Tensile strength | ≥15Pa |
| Sealability | N/50mm 3300 |
| Service life | ≥10 years (normal operating conditions) |
| Outer skin temperature | Long-term ≤250℃, short-term ≤350℃; External surface temperature ≤50℃ after installation (with thermal insulation filler) |
5. Key points of selection of fabric expansion joint skin
The working condition parameters must be considered comprehensively in the selection of fabric expansion joint skin. The selection of skin directly determines the use effect of expansion joint.
1. Determining Media Temperature and Corrosivity
- ≤600℃ and average corrosivity: silicone skin
600℃ or strong acid and strong alkali environment: fluorine glue skin
2. Calculate working pressure and displacement
- Calculation of thermal displacement based on pipe diameter, length, and temperature changes
- The skin needs to absorb three-way displacement (axial, transverse, angular)
- Structural reinforcement layer needs to be added in high pressure or high negative pressure environment
3. Drainage design
When the desulfurization flue is installed horizontally, drainage holes must be installed on the expansion joint to avoid the accumulation of acidic condensate and corrosion of the skin.
4. Installation and fastening requirements
- The skin of the non-metallic expansion joint is made of soft fabric material, and the fixing bolt needs to be tightened repeatedly
- During installation, fix the skin on one side and tightly seal on the other side to prevent acid water from penetrating and corroding the screws
VI. Frequently asked questions and maintenance suggestions
Common causes of damage to fabric expansion joint skin include:
- Improper selection: Misuse of silicone skin when fluorine skin should be selected, resulting in insufficient corrosion resistance
- Loose mounting bolts: not repeatedly tightened according to specifications, resulting in acid water infiltration and corrosion
- Horizontal installation without drainage hole: condensate accumulation corrodes skin
Maintenance recommendations:
- Regularly check the skin surface for damage and aging
- Check the tightening state of the bolts and tighten them again in time
- Small holes can be repaired with special glue, and the skin needs to be replaced if serious damage is found
- Dredge drainage holes regularly to prevent clogging
sum up
The skin of fabric expansion joint is the core flexible element of non-metallic expansion joint. Its selection and construction quality directly determine the overall performance and service life of expansion joint. The following principles should be followed in the correct selection:
| gist | Core Content |
|---|---|
| Structural cognition | The skin is a composite structure comprising a sealing layer, an insulating layer, a reinforcing layer, and an outer protective layer |
| Material selection | The temperature resistance of silicone skin is ≤600℃, the temperature resistance of fluorine skin is ≤1200℃ and the corrosion resistance is better |
| Execution standards | Ministry of Machinery Standard JBT 12235-2015, National Standard GB/T 12777-2019 |
| Drainage design | Horizontal flue must be equipped with drainage holes to prevent acid accumulation |
| Installation Points | The bolts are repeatedly tightened and regularly tightened after commissioning |
| Life expectancy | Normal working conditions ≥5 years (technical requirements of power plants), some can be more than 10 years |
The fabric expansion joint skin with reasonable design and standard selection can run stably for a long time under harsh working conditions such as high temperature and corrosion, and provide reliable flexible connection guarantee for flue gas system. It is recommended to clarify the working condition parameters in the design stage, and make customized selection by professional manufacturers, and strictly accept according to standards.