High-temperature flue gases, corrosive media, and mechanical vibration are long-standing challenges in industrial pipeline systems. Traditional metal expansion joints, despite their high strength, are often inadequate when dealing with multidirectional displacements, corrosive environments and vibration isolation. Fabric expansion joints (also known as non-metallic fabric compensators) are becoming ideal for hot air ducts, flue gas desulfurization systems, and ventilation and dust removal with their unique flexible structure. This article will give you a comprehensive analysis of this important pipeline compensation device from structural composition, working principle, performance characteristics to type selection and installation.
I. What is a fabric expansion joint?
Fabric expansion joint is a pipeline compensation device with non-metallic materials such as fiber fabric as the core elastic element. It is mainly used in low-pressure ventilation, dust removal, smoke exhaust and air conditioning heat preservation pipeline system。 Different from the traditional metal bellows expansion joint, it realizes the multi-dimensional displacement compensation caused by temperature change, mechanical vibration and foundation subsidence through the deformation of flexible material。
The product is widely used in steel plants, smelters, petrochemical plants, thermal power plants, cement plants, nuclear power plants and other industrial fields. It is especially suitable for hot air ducts and smoke and dust ducts。
2. Structural composition of fabric expansion joint
Understanding the structure of fabric expansion joints is the basis for proper selection and installation. A complete fabric expansion joint mainly consists of the following parts:
1. Skin (core telescopic body)
The skin is the most critical component of fabric expansion joint, which is composed of multi-layer non-metallic fabric composite materials. Combination design according to working conditions (temperature, medium corrosivity), commonly used materials include:
- Fiberglass cloth: Provides base strength and temperature resistance
- Silicone/Fluorine Tape: Enhanced High Temperature and Corrosion Resistance
- PTFE Film: Provides Excellent Chemical Inertness and Sealing
- Aluminum silicate fiber cotton/ceramic fiber cloth: for high temperature insulation
The number of layers of the skin can be designed as single layer or multiple layers according to the working conditions. The multilayer structure not only enhances mechanical strength, but also enables functional zoning for different environmental conditions: the outer layer resists environmental corrosion, and the inner layer enables heat preservation and sealing。
2. Metal frame (rack)
The metal frame is a contoured bracket for the fabric expansion joint, which guarantees the product to have sufficient strength and rigidity. The frame material is selected according to the medium temperature:
3. Guide tube (baffle)
The guide tube plays the role of deflecting flow and protecting the heat insulation layer. When installing, ensure that the direction of its arrow is consistent with the direction of medium flow in the pipeline. The material shall be compatible with the medium temperature and have corrosion and wear resistance properties。
4. Thermal insulation layer
It is composed of multi-layer ceramic fiber and other high temperature resistant materials, and its thickness is determined by heat transfer calculation according to the medium temperature and thermal conductivity, which is the key to ensure the heat insulation performance of fabric expansion joint。
5. Stainless steel wire mesh
It is used as an inner liner to prevent impurities in the circulating medium from entering the expansion joint, and at the same time to prevent the outward dissipation of the heat insulating material。
3. Working principle of fabric expansion joint
The core working principle of fabric expansion joint can be summarized as "flexible deformation to absorb displacement". Unlike metal expansion joints, which rely on the elastic deformation of metal corrugations, fabric expansion joints achieve displacement compensation through the foldable and stretchable characteristics of fibrous fabrics.
When the pipe is elongated by heat, the skin material produces compression deformation in the length direction; When the pipe shrinks, the skin develops tensile deformation. Because the fabric material has an extremely low elastic modulus (almost zero spring stiffness), it absorbs displacement while transmitting little reverse thrust to the piping system。 This feature allows it to significantly simplify the design of pipe supports, avoid the use of large fixed supports, and save a lot of material and labor。
In terms of sealing mechanism, the outer hermetic membrane of the fabric expansion joint is usually composed of a woven fabric plus an elastomeric coating. The fiber provides strength and flexibility, and the coating protects the fiber from chemical attack and seals the fabric, minimizing media leakage。
4. Core Features of Fabric Expansion Joints
1. Multi-directional compensation ability
Fabric expansion joints can compensate axial, transverse and angular displacements simultaneously, which is greatly superior to metal compensators that can only compensate in one direction。 For example, all-round compensation of ±200mm in the axial direction, ±150mm in the lateral direction, and ±10° in the angular direction can be provided in a smaller space 。
2. No reverse thrust
Because the main material is fiber fabric, weak transmission characteristics. The use of fabric expansion joints can reduce the reverse thrust of the system to less than 1/10 of the metal compensator, thus simplifying the design of pipe support structure。
3. Noise and vibration isolation
Fiber fabric and heat insulation cotton have the functions of sound absorption and vibration isolation. The measured noise reduction can reach 25dB (A), and the vibration isolation efficiency exceeds 80%, which can effectively reduce the noise and vibration of boiler, fan and other systems。
4. High temperature resistance and corrosion resistance
The selected fluoroplastics and silicone materials have excellent high temperature resistance and corrosion resistance. Conventional materials can withstand temperature ranges from-70℃ to 260℃, and special materials such as ceramic fiber cloth can withstand instantaneous high temperatures up to 1770℃。 It performs particularly well in corrosive environments such as flue gas desulfurization.
5. Good sealing performance
Using perfect production and assembly technology, fabric expansion joint can achieve basically leakage-free operation。
6. Lightweight and easy maintenance
Weighs about 1/3 to 1/2 of the metal compensator. Components such as skin can be replaced separately, eliminating the need to remove the frame in its entirety, significantly reducing maintenance costs。
Main Types and Application Scenarios
6. Key points of selection and installation
Parameters required for selection
- Operating temperature (max/min/instantaneous)
- Working Pressure and Pressure Fluctuation Range
- Media composition and corrosivity
- Required compensation amount (axial, lateral, angular)
- Pipe diameter and connection method
Installation Considerations
- Check the specification and pressure level before installation, and check the surface for any bumps and scratches
- Note that that direction of the guide tube arrow must coincide with the flow direction of the medium
- Flange bolts shall be tightened evenly and symmetrically
- When welding operation, cover should be used to protect the skin to prevent the damage of welding slag
Conclusion: Reasonable selection to improve system reliability
With its multi-directional compensation, no reverse thrust, noise and vibration isolation and excellent corrosion resistance, fabric expansion joints have become indispensable pipe connection elements in the fields of hot air ducts, flue gas desulfurization systems and ventilation and dust removal. The correct selection and use of fabric expansion joints can not only extend the life of the piping system, but also significantly reduce maintenance costs and safety risks.