In industrial flue gas treatment system, fabric expansion joint flue is the key flexible component connecting boiler, desulfurization tower, dust collector and other equipment. Different from traditional metal expansion joints, fabric expansion joints use fiber fabric as the core elastic element, so they are also called non-metallic expansion joints or fiber fabric compensators。 Under the condition of the same shape and size, the compensation ability of lateral displacement far exceeds that of metal expansion joint, and it hardly produces reverse thrust. It is especially suitable for flue duct systems in power plants, metallurgy, cement and other industries。 This paper will systematically explain the professional technical knowledge of fabric expansion joint flue from structural characteristics, material selection to installation and maintenance.
1. Structure and working principle of fabric expansion joint flue
The core working body of fabric expansion joint flue is a non-metal band composed of fiber fabric composite materials. The research shows that the non-metallic compensator is composed of non-metallic skin, heat insulation packing, guide tube, pressure plate, fastener, etc. It can compensate displacement, isolate vibration source and reduce vibration and noise。 When the flue expands under heat, the fibrous fabric absorbs the thermal displacement through its own elastic deformation; When the temperature drops, it can return to its original state.
The unique feature of fabric expansion joint flue is that it adopts a large circular arc transition corner structure to form a rectangular cross section. The stress level of the corner section is reduced, the dead corner of deformation and the uniform deformation of the whole product during online operation are eliminated, thus reducing the risk of regional high stress damage and prolonging the service life of the product。 The structure design can reduce the thrust of the pipe system and improve the thermal compensation ability of the product under the condition that the whole system is not unstable and the basic working stiffness is maintained。
Comparison of core strengths
| Contrast dimension | fabric expansion joint | Metal expansion joint |
|---|---|---|
| Displacement compensation | Strong three-way compensation ability | Mainly axial |
| Reverse thrust | No reverse thrust | Large blind plate force |
| Vibration isolation effect | Excellent | normal |
| Installation difficulty | simple | Complicated |
| Comprehensive costs | lower | Higher |
The research shows that the fiber compensator can simplify the design, avoid the use of large supports, and save a lot of material and labor because the main material is fiber fabric, which has weak transmission。
2. Material selection of fabric expansion joint flue
The skin of the fabric expansion joint flue is composed of a variety of high-performance fiber fabrics, and different levels perform their respective duties:
| Structural hierarchy | Materials | function |
|---|---|---|
| Dielectric contact layer | Fluorine rubber cloth | Corrosion and high temperature resistance |
| Sealing layer | PTFE membrane/PTFE cloth | Ensure airtightness |
| Reinforcement layer | Alkali-free fiberglass cloth/wire-clamped fiberglass cloth | Provide strength |
| Thermal insulation | Aluminum silicate insulation cotton | Lowering the external surface temperature |
| Outer protective layer | Silicone rubber cloth | Weather Resistance, Protection |
Temperature grade selection: The main material used for low temperature non-metallic compensator is silicone cloth skin, and the main material used for high temperature non-metallic compensator is fluorine cloth skin。
Special working condition requirements:
- It is used for transporting desulfurization pipeline system with acidity and alkalinity. In order to avoid corrosion of skin caused by accumulation of cooling water, a drainage device is required
- It is used for hot air and smoke discharge in steel plants, power plants, cement plants, etc. It is necessary to add asbestos layer inside the non-metallic skin to achieve flame retardant and fire resistant function
3. Design points of fabric expansion joint flue
Deflector design
The deflector in the flue of fabric expansion joint is the key component to protect the skin. Industry experts pointed out that the deflector material needs to have sufficient stiffness and strength, and the thickness is determined according to the flow rate and pressure of the medium, generally ≥3mm. The deflector shall cover the body of the expansion joint of the fiber fabric during installation, so as to avoid direct washing of the fabric by the medium。
Gap control: The gap between the deflector and the expansion joint of the fiber fabric is generally kept at 5-10mm, so as to avoid friction between the expansion joint and the deflector when it expands and contracts, and at the same time to prevent media from penetrating into the corroded fabric from the gap。
Inclination angle: For particulate matter and dust media, the deflector plate should be extra smooth. If necessary, it can be designed at an inclined angle, which is 15-30° with the flow direction of the medium, so as to further increase the impact resistance。
Drainage design
The fabric expansion joint flue that is exposed to wet flue gas and is located in the horizontal flue section needs to be drained through the expansion joint frame with a drain hole of at least DN150 and located on the centerline of the horizontal flue section. Drainage fittings are made of FRP or nickel-based alloy steel material and drain water back to the drainage pit in the FGD area。
Execution standards
The design and manufacture of fabric expansion joint flue shall follow industry standards. The non-metallic compensator implements "JB/T12235-2015", and can be provided in various structural forms such as circular, rectangular (square), rounded sky and place。 The working pressure range of the product is generally-20~30kPa, the temperature range is standard type ≤450℃, and the high temperature customized type can reach 800~1100℃。
IV. Installation specification of fabric expansion joint flue
The installation quality of fabric expansion joint flue directly affects its service life. Combining multiple industry sources, the following deviation requirements should be met during installation：
| Installation Project | Allowable deviation |
|---|---|
| Installation length | ±5mm |
| Coaxiality | ±5mm |
| Torsion angle | ≤10° |
| Offset angle | ±0.1° |
Key Installation Points:
- Flow direction confirmation: The non-metallic compensator is equipped with a transport fixed rod. After the installation is complete, remove the pull rod or fixed rod marked with yellow to ensure the normal operation of the compensator。 The marking direction of the wear-resistant bushing must be consistent with the flow direction of the pipeline medium。
- Bolt tightening: When flanged connection, the bolts should be gradually and evenly pressurized and tightened, and the tightness of all screws and bolts should be as consistent as possible. In the case of bad working conditions, spring washers can be added to prevent nut loosening。
- Welding protection: If a connection is adopted or there is a welding operation nearby, the rubber or fabric surface should be covered to prevent welding slag from damaging the product。
- Installation in natural state: When installing non-metallic compensator, care should be taken to keep the compensator in natural state without artificial deformation。
V. Maintenance and management of fabric expansion joint flue
The routine maintenance of fabric expansion joint flue is a key link to prolong the service life.
Periodic inspection
It is recommended that the non-metallic bands should be regularly checked for wear, aging or damage, the sealing performance is good, and the dust and debris accumulated on the surface should be cleaned up in time。 Use of non-metals in desulfurization towers When compensator, pay attention to corrosion protection; When used in high friction environments, replace the skin regularly。
troubleshooting
- Small vulnerability repair: Special glue can be used to repair it
- Serious damage: skin replacement
- Normal replacement cycle: the normal life of non-metallic skin is about 5 years
Important warning: Although the non-metallic compensator has strong temperature resistance, care should be taken to prevent open flame ignition during installation and use。 During installation, if there is welding, pay attention to protect the insulation layer of the compensator, especially the outer skin of the product is easily ignited by the shedding welding slag。
6. Typical Application of Fabric Expansion Joint Flue
Fabric expansion joint flue is widely used in various industrial fields：
| Application industry | Typical location | Characteristics of working conditions |
|---|---|---|
| Thermal power generation | Boiler flue, desulfurization flue | High temperature, sulfur, corrosion |
| Iron and steel metallurgy | Hot air duct, dust removal duct | High temperature, dusty |
| Cement building materials | Kiln tail flue, preheater | High temperature, wear |
| Petrochemical industry | Catalytic cracking flue | High temperature, corrosion |
In the pipeline system, if there are simultaneous thermal stress caused by temperature change, local stress caused by vibration of equipment and fixed support, and stress caused by system installation deviation, the use of hard connection mode will inevitably lead to deformation or failure of the pipeline system at the weakest point. The use of flexible non-metallic compensator can avoid the occurrence of such damage。
sum up
Fabric expansion joint flue is an indispensable flexible connection device in modern industrial flue gas system. Its core strengths can be summarized as follows:
| gist | Core Content |
|---|---|
| Structure and principle | The elastic deformation of the fiber fabric absorbs the heat displacement, and the large arc transition corner structure reduces the stress concentration |
| Material selection | Silicone rubber for low temperature, fluororubber for high temperature, dusty working condition with deflector (thickness ≥3mm, gap 5-10mm) |
| Installation Specifications | Coaxiality ±5mm, the flow direction marks are consistent. After installation, remove the transport tie rod and tighten the bolts in stages |
| Execution standards | JB/T12235-2015, working pressure-20~30kPa, temperature range ≤450℃ (standard type) to 1100℃ (high temperature type) |
| Maintenance cycle | The normal life is about 5 years, small holes can be repaired, serious damage needs to be replaced skin |
The fabric expansion joint flue with reasonable design and standard installation can effectively solve the problems of thermal stress, vibration and installation deviation of pipeline system, and significantly improve the stability and economy of system operation。 It is recommended that the working condition parameters (temperature, corrosivity, displacement) be clarified at the design stage, and the professional manufacturers will make customized selection.