Are non-metallic soft connections (compensators) IQ taxes? Disassembly one by one from structure, temperature resistance to life

Find out first: What exactly is a non-metallic soft connection (compensator)?

Non-metallic soft connection, also called non-metallic compensator, non-metallic expansion joint-you look through the product catalog in our site,Non-metallic expansion joint (fabric fiber expansion joint)、rubber compensator、PTFE compensatorIt's all in this category. To put it bluntly, this thing is a piece of "cartilage head" installed in the middle of a pipe to absorb the displacement caused by thermal expansion and contraction, vibration or installation error. Different from metal expansion joints, it mainly relies on non-metallic materials such as fabrics, rubber and fluoroplastics to compensate for deformation.

When many people hear "non-metal", they think is it cutting corners? The price is a lot cheaper than the metal expansion joint. Don't be IQ tax, right? Two days ago, I met a buddy who was engaged in cement plant purchasing, and I asked this when I came up. Today, let's take apart its structure, materials, ability and life to see if it is worth the money.

Structural disassembly: fabric, rubber, PTFE... different materials, how much difference is the ability?

The outer layer is a weather-resistant silicone rubber or fluororubber coated fabric, the middle is a thermal insulation layer (such as ceramic fiber cotton), and the inner layer is corrosion-resistant polytetrafluoroethylene (PTFE) or fluororubber. The working conditions corresponding to different materials were not even a little different.

• Fabric fibers(That's what we saidNon-metallic expansion joint (fabric fiber expansion joint)): The maximum temperature resistance can reach above 1000℃, depending on the braided layer of ceramic fiber and glass fiber. It is suitable for high-temperature flue gas pipelines in power station boilers and cement kilns. However, the disadvantage is that it is not resistant to high pressure, and can generally only be used under negative pressure or slightly positive pressure from several kPa to tens of kPa.
• Rubber（rubber compensator): Mainly use EPDM, neoprene or fluororubber. The temperature resistance range is-40℃ to 200℃ (fluororubber can reach 250℃), and the pressure resistance can reach 1.0MPa or even higher. Suitable for water, air, dilute acid and other media. However, it is afraid of oil and ozone aging, and its life is generally 5-8 years.
• Tetrafluorine（PTFE compensator、Rubber PTFE compensator): Lined with PTFE film or integral molding, it has strong corrosion resistance and can carry almost all strong acids and alkali. Temperature resistance-20℃ to 200℃, but PTFE itself has poor elasticity, so it is often used in combination with rubber or bellows.

You see, when the materials change, the capabilities are very different. If you choose the wrong choice, it is not an IQ tax, but a mine for yourself.

Compared with the metal expansion joint, where does the non-metal soft connection (compensator) lose and win?

Metal expansion joints-like the ones in our stationUniversal corrugated expansion joint、High temperature axial expansion joint、Corrugated expansion joint for power station industry-They rely on the deformation of stainless steel bellows to compensate for displacement, and have high pressure resistance and long life (a design life of 10 years is common). However, non-metallic soft connections also have advantages that metals can't compare:

Where to win:

• Large compensation displacement: Non-metallic soft connections can easily absorb multi-directional displacements, especially lateral and angular displacements, whereas metal bellows are usually only suitable for axial directions.
• Good vibration and noise reduction: Fabric and rubber themselves are damping materials, which can eat the vibration of the pipeline. Metal expansion joints often depend on adding dampers.
• Low cost and light installation: Under the same caliber, the weight of non-metallic soft connections is only 1/3 or even lighter than that of metal, and the price is more than half cheaper. For large-diameter air ducts (two or three meters in diameter), people can cry with metal expansion knuckle flanges.
• Corrosion resistance (for smoke): Metals are afraid of chloride ion stress corrosion, but non-metallic PTFE and rubber are not afraid at all.

Where to lose:

• Low pressure resistance, high-pressure pipeline (> 0.5MPa) basically does not need to be considered.
• Although the temperature resistance can be very high instantly, the upper limit of long-term use temperature is lower than that of metal (metal bellows with ceramic fiber lining can achieve a long-term temperature above 1000℃).
• Short life, fabrics usually need to be replaced in 3-5 years, while metal expansion joints can last for 10 years when well maintained.

Therefore, there is no one who is higher or lower, only whether it is suitable or not. Non-metal soft connection is the king in low pressure and large displacement conditions such as flue gas, dust removal, desulfurization and denitrification; But in steam and high-pressure oil pipes, hard on non-metal is looking for death.

Selection and avoidance of pits: temperature, pressure, medium, displacement, if you look less than one, you will have an accident

He bought itRectangular non-metallic expansion jointIt was used at the entrance of the desulfurization tower, but it leaked after two months. When asked, he regarded the working temperature of 200℃ as long-term temperature resistance. In fact, the sustained temperature resistance of the fabric compensator was only 150℃. This kind of pit, stepping into it is not just a matter of money-the loss of one day's downtime is enough to buy more than a dozen compensators.

• Temperature: Distinguish between "long-term operating temperature" and "instantaneous peak temperature". For example, ceramic fiber fabric can withstand 1200℃ instantly, but it begins to powder when it exceeds 600℃ for a long time.
• pressure: Non-metallic soft connection is generally used in negative pressure or ≤0.1MPa working condition. If the pressure exceeds, a structure with a metal skeleton or reinforcement layer must be selected. There are some in our stationRubber PTFE compensatorIt can reach 1.0MPa, but that's a special case.
• Medium: SO₂ and NOx in flue gas, or chloride ions in desulfurization slurry, are corrosive to rubber and fabrics. Fluororubber, PTFE lining is the right way.
• displacement amount: It is necessary to calculate the displacement in axial, transverse and angular directions, especially the multidirectional compound displacement. Although the non-metallic soft connection can absorb, it must be designed with an allowance, otherwise the fabric will be torn.

Look less at one parameter, from early failure to pipeline cracking. You can only take the blame yourself, don't blame the supplier.

Installation and life: Don't let a single bolt ruin the entire compensator

What are non-metallic soft connections most afraid of? The flange bolts are tightened too tightly or not tightly during installation. Tightening too tightly will crack the fabric layer, and if it is not tight in place, it will leak air. The correct way is to use a torque wrench and tighten it three times in diagonal order. Refer to the manufacturer's instructions for the torque value. Don't be lazy.

In addition, be sure to see if the guide bracket and fixed bracket of the pipe are done correctly. The non-metallic soft connection itself can't bear the blind plate force of the pipeline. If the fixed bracket is not set properly, the thrust generated by thermal expansion will directly pull the compensator out-I have seen this situation more than once, and finally I found that the installation team was greedy and the bracket welding was crooked.

Well, under normal working conditions: 3-5 years for rubber compensator, 5-8 years for fabric fiber expansion joint, and more than 10 years for PTFE compensator. However, if the ambient temperature exceeds the standard for a long time and the medium contains particulate matter, the life span will be cut in half. Regularly check the coating for cracks and the flange interface for leakage. It is no problem to survive an overhaul cycle.

Practical case: power station, cement, desulfurization and denitrification, which working conditions must be on non-metallic soft connection?

• Flue of power station boiler: Between the air preheater and the dust collector, the flue gas temperature is 150-180℃, negative pressure, and the huge displacement when the boiler starts and stops is absorbed. This kind of working condition is often pushed in our stationNon-metallic expansion joint (fabric fiber expansion joint), cooperate withFlue gas baffle doorOrRound Flap Door (Double Seal)Isolate smoke. The metal expansion joint is easily cracked by chloride ion stress corrosion at this position.
• Kiln tail of cement industry: The temperature is high (300-400℃), the dust is large, and the three-dimensional displacement needs to be compensated. useRectangular non-metallic expansion jointCooperateMetal Corrugated Expansion Joints in Cement IndustryFor combination compensation, metallic ones are used to withstand pressure, and non-metallic ones are used to absorb multi-directional displacement.
• Desulfurization and denitrification system: Clean flue gas after wet desulfurization, with low temperature (50-80℃) but high humidity and corrosive liquid. Under such operating conditionsrubber compensator(lined with PTFE) andDesulfurization flue gas baffle doorIt's a golden partner. Corrosion resistance, good sealing and light installation, metal expansion joints are prone to problems due to electrochemical corrosion.

You see, these places use non-metal soft connections not to be cheap, it is really better than metal. IQ tax? The tax is on those who buy blindly without looking at the parameters. As long as the working conditions are right, the selection is right, and the installation is right, this thing is a cost-effective artifact.