What is a non-metallic flexible fabric compensator expansion joint? What is the essential difference between it and traditional metal compensators?
To put it bluntly, the expansion joint of non-metallic flexible fabric compensator is the "soft joint" of the pipeline-made of multi-layer fabric fibers, silica gel, polytetrafluoroethylene and other non-metallic materials, which can absorb the thermal expansion, contraction and vibration of the pipeline. And those stainless steel bellows (like our siteUniversal corrugated expansion joint、The high-temperature axial expansion joint is different from the head-on. This thing is deformed by the flexibility and slip between layers of the fabric itself, rather than by the elastic deformation of the metal.
What's the difference? Metal compensators carry high pressure and long life, but stainless steel can't carry corrosive media or high-temperature flue gas. The non-metallic fabric compensator expansion joint has a wide temperature resistance range (-40℃ to 1200℃ is no problem), acid and alkali corrosion resistance, and the price is only half that of metal or even less. The disadvantage is that the pressure bearing capacity is weak, generally not more than 0.1MPa (about 1 kg force). So it is not here to replace metal, it is here to fill-it is even the only option under certain operating conditions.
Practical scenario: Under which operating conditions are non-metallic fabric compensators the only choice?
Two days ago, I met the project manager of a cement factory. The outlet pipe of the rotary kiln in his factory, with a temperature of about 900℃, contained a lot of sulfur dioxide and dust. With metal bellows? Corroded perforations in three months. Later, I changed this station'sNon-metallic expansion joint (fabric fiber expansion joint)Two years of running without problems. Why? High silicon fiber and polytetrafluoroethylene film are used in the fabric layer, which is temperature-resistant and acid-resistant, and the soft structure is not afraid of dust accumulation.
Here's another example of the power station industry. At the inlet and outlet of the desulfurization tower, the flue gas temperature is about 120℃, and the humidity is saturated with sulfuric acid droplets. Under this working condition, the metalDesulfurization flue gas baffle doorIt can be used, but if you still use metal expansion joints for pipeline compensation, chloride ion stress corrosion cracking will teach you how to be a person in minutes. Replace non-metallic, lined with PTFE layer, and strengthened with outer fabric, reducing the cost by 40% and doubling the maintenance cycle.
There are also flue gas pipelines of waste incineration power plants, with complicated working conditions: large temperature fluctuations (from normal temperature to 850℃), containing strong corrosive gases such as HCl and SOx. Because of the layered design, the expansion joint of non-metallic fabric compensator can take into account both heat insulation and corrosion protection at the same time, while the metal expansion joint should be either added with high-priced alloy or scrapped regularly under this working condition.
Selection and Pit Avoidance Guide: Temperature, Pressure, Medium, Displacement-Don't Make Mistake Four Parameters
Many customers come up and ask "Give me a non-metallic compensator, DN500". Stop! Non-metallic compensators are not standard parts and must be customized according to working conditions. If one of the four core parameters is wrong, the equipment will be wasted.
- Temperature:Don't just look at the average, look at the peak and the frequency of fluctuations. For example, the flue gas temperature is nominal to 250℃, but it may instantly rush to 350℃ when starting and shutting down. At this time, the candidate rubber compensator (temperature resistance limit 150℃) is finished, and a silicone + glass fiber fabric compensator must be used. This site'srubber compensatorOnly suitable for low temperature water systems, don't use it wrong.
- Pressure:Non-metallic fabric compensator expansion joints are generally used in atmospheric pressure or slightly positive pressure (≤0.05MPa) pipes. Beyond this value, consider structures with metal mesh reinforcement, or simply useMetal hoseOrCovered hinge transverse expansion joint. Don't try the high pressure condition at the fan outlet.
- Media:For flue gas containing oil and dust, choose oil-proof coating lining; Strong acid-base environment, preferredPTFE compensator orLined with PTFE hose (if pressure is high). If the media composition list is not clear, you can send a sample for corrosion simulation.
- Displacement Amount:The non-metallic compensator has a strong ability to absorb axial displacement (generally up to ±100mm), but the lateral displacement is limited. If the pipeline is L-shaped or Z-shaped, it is necessary to calculate the resultant displacement. If necessary, connect two in series or optionallyRectangular non-metallic expansion joint (for rectangular pipes). Don't place an order just by looking at it, and you will regret it if it is broken after installing it.
Installation and maintenance: Don't let a small oversight destroy the entire compensator
Last year, there was a customer who installed a non-metallic fabric compensator and the expansion joint leaked after only six months. When I went to the door, I found that the tie rod bolts for transportation were not removed during installation. The bolt was originally designed to prevent deformation during transportation, and must be loosened or removed after installation to allow the compensator to expand and contract freely. If the customer didn't dismantle it, it was equivalent to locking the compensator abruptly. When the pipe expands thermally, it doesn't move, and the temperature stress is all transmitted to the flange and equipment, and finally the fabric is torn. Remember: This site'sHow to adjust the tie rod nut of expansion jointIt is clear in this question and answer-the screw must be removed, and the locking nut must be loosened after the tie rod nut is adjusted to the fixed position.
- Misaligned installation: The flange surfaces are not aligned, and the bolts are forcibly pulled together, resulting in twisted fabric layer. It is required that the error of flange parallelism should not exceed 2mm.
- The insulation layer is directly pressed on the compensator: many construction teams try to save trouble and crush the insulation cotton to death on the surface of the compensator. As a result, the fabric layer can't expand and contract normally, and the life is halved. The correct way to do this is to leave a 50-100mm gap or use a separate removable insulation sleeve.
- Ignoring the guide tube: If there is particulate material washing in the pipeline, the guide tube must be added (refer to this siteSpecific Function of Expansion Joint Guide Tube）。 There are many in this siteMetal Corrugated Expansion Joints in Cement IndustryIn fact, the non-metallic compensator is also needed, otherwise the high-speed particles will break the fabric layer.
Comparison Summary: Non-Metal vs Metal, Who Should I Choose When? When do you have to change?
Come on, just give the conclusion.
Selection of non-metallic flexible fabric compensator expansion joint:
- The medium temperature exceeds 400℃ but the pressure is ≤0.1MPa
- The medium contains strong acids, strong bases, chloride ions, etc
- The diameter of the pipe is oversized (above DN2000), and the metal compensator is too expensive and heavy
- Need vibration and noise isolation, such as fan inlet and outlet
- Limited installation space allows large displacements but does not require high pressure
Case of Metal Compensator Selection:
- Pressure ≥0.1MPa, even medium to high pressure (such as steam pipes, usingsteam pipe corrugated expansion joint)
- The medium is pure and non-corrosive, or weakly corrosive
- There are stringent requirements for leakage rate (the non-metallic fabric layer will have trace penetration over time)
- Requires to withstand axial reaction forces (non-metals cannot withstand thrust)
When do you have to change? When you find that the existing metal compensator is frequently corroded and perforated, or the vibration and noise are excessive, or the budget really can't be cut-then switch to a non-metallic fabric compensator expansion joint. Conversely, if the non-metallic compensator you use has fabric aging, peeling between layers, or bulging caused by unstable pressure, it means that the original selection was incorrect, and you should go back and re-check the parameters, or cut back to the metal scheme (such as this site'sMetal rectangular expansion joint,External pressure single axial type expansion joint, etc.).
No matter which one you choose, don't ignore the matching onesFlue gas baffle doorOrPlug-in insulation door。 The valve and the compensator are a pair of partners. If the valve is not closed properly, the compensator is washed out that is useless. Choose the right one time and save five years of worry.