1. What is the upper limit of temperature resistance? Don't be fooled by the word "high temperature resistance"
When a customer comes up, he asks, "How many degrees can your non-metallic expansion joint withstand?" I generally ask, "Tell me first what the working medium is and what the temperature fluctuation range is." Why? Because the upper temperature resistance limit of non-metallic expansion joints (to put it bluntly, fabric fiber expansion joints) completely depends on the skin material.
The combination of silicone cloth + glass fiber can be carried to about 250℃ conventionally, but barely to 280℃ under extreme working conditions. If you use fluororubber interlayer, you can touch it up to 300℃. But if you exceed 350℃-sorry, the non-metal scheme basically stops. You have to look honestly at this timeHigh temperature axial expansion jointOr a metal bellows scheme.
The standard JB/T 12235-2015 has clear requirements for the temperature resistance test method: it is not the manufacturer who says "high temperature resistance", but you have to check the material table with the working temperature. For example, in the desulfurization flue gas pipeline, the medium temperature hovers at 150~200℃ all the year round, so silicone cloth + glass fiber is completely enough. But if anyone dares to use this to fight the 350℃ steam pipe, tsk, the skin will be brittle and cracked in less than two months.
Therefore, when selecting a model, don't just look at the big characters printed on the propaganda page. Put out the temperature, media composition and pressure, one by one. The first threshold of whether the performance of non-metallic expansion joints is reliable is temperature matching.
2. Compensation displacement depends on "soft", but soft also has soft truth
The compensation ability of non-metallic expansion joint is indeed much stronger than that of metal bellows with the same diameter. It can eat several times the displacement of metal in axial, transverse and angular directions. Especially rectangular pipes-think about it, flue, air duct and dust removal pipes are basically all square. Metal corrugated pipes have to make rectangular structures, and the process is complicated and costly, butRectangular non-metallic expansion jointA single loop of fabric can absorb tens of millimeters of displacement, and it saves a lot of installation space.
Two days ago, I encountered a project of dust removal system. The lateral displacement of the corner of the pipe was 30mm. If you use metal bellows, you have to pile four or five waves, and you have to add guide brackets. Switch to non-metallic ones and get it done in one circle. What about the cost? Weak pressure bearing capacity-non-metallic expansion joints are generally only used in low-pressure systems of 0.1~0.5MPa, and flue gas pipelines, dust removal systems, fan inlet and outlet are its home fields. You said that if you attack the steam pipe, as soon as the pressure comes up, the fabric will bulge and tear apart, and the accident will not escape.
Therefore, "soft" is both an advantage and a short board. You use the right place, and it works better than anyone else; Use it wrong, that's a ticking time bomb.
3. Corrosion resistance and sealing: the "best partner" next to the desulfurization flue gas baffle door
In the desulfurization and denitrification system, SO₂, HCl, acid-alkali mist, etc. are simply "solvents" for metal bellows. Stainless steel bellows are perforated in a few months in the face of acid dew point corrosion. However, the non-metallic expansion joint is different-the main body of the skin is a composite layer of fabric + rubber/fluoroplastic, which is not afraid of corrosion by these acidic media.
In front and behind the desulfurization flue gas baffle door of a power plant, the original metal bellows was changed three times in a year and a half. Later replaced withNon-metallic expansion joint (fabric fiber expansion joint), cooperate withDesulfurization flue gas baffle doorUsed together, and there has been no leak in three years. Why? Because the non-metallic elastic seal can automatically compensate for installation deviations, the pipe is misaligned? No problem, once the skin is pressed, the leakage will be directly plugged. However, the installation requirements of metal bellows are high, and air leakage will occur if it is slightly biased.
Is that the truth? When you buy a non-metallic expansion joint, the picture is its "leather solid" in this scene. However, note that if the medium contains particulate matter and scour seriously, an additional wear-resistant layer should be added, or considerrubber compensator— — Different structures have different life performance.
4. How long is the lifespan? Can it last 5 years? People ask every day
Under normal working conditions, this classic three-layer structure of inner fluororubber + middle glass fiber cloth + outer silicone cloth can be used for 3~5 years without fault. But the premise is-don't fluctuate too frequently, the corrosion sex of the medium exceeds the standard, and don't use dust as air to blow.
Frequency of temperature fluctuations, corrosiveness of media, mechanical wear (e.g. dust washing). Think about it, the same model may be changed in three years when used in the flue of a power plant, but it is still fine when used in the air conditioning ventilation duct for seven or eight years. The difference is the working conditions.
In addition, there are more pits in the installation link. Such asHow to adjust the tie rod nut of expansion joint？ If the preloading force is not properly adjusted, either the skin is too tight and loses the ability to compensate, or it is too loose to cause vibration tear. Another exampleexpansion joint guide tubeInstall it backwards-the direction of the guide tube is opposite to the flow direction of the medium, and the airflow directly impacts the skin, and the life is directly folded in half. For these details, the manufacturer will not stare at your installation site, but can only check it by itself.
Therefore, asking "How long is the performance life of non-metallic expansion joints" is better than asking "How can I prolong the life under this working condition". It is not difficult to add wear-resistant layer, choose the right skin thickness, and regularly check the preloading force. To do these things, it is really not difficult to use it for 5 years.
5. The most afraid thing in model selection: Take non-metallic expansion joints as universal patches
As soon as some customers see that non-metallic expansion joints are cheap and light to install, they slap their foreheads on the high-pressure steam pipeline. Then there must be an accident-if the pressure exceeds 0.5MPa and the temperature exceeds 350℃, don't touch non-metals. Choose honestlyUniversal corrugated expansion jointOrExternal pressure single axial expansion joint。 Or, the high-temperature axial expansion joint specializes in this job, so don't save money blindly.
Round non-metallic expansion joints for rectangular pipes, or vice versa. Rectangular ones must beRectangular non-metallic expansion joint, circular withNon-metallic expansion joint (fabric fiber expansion joint)Don't mix it. Why? Shape mismatch, stress concentration at flange joints, it didn't take long to collapse.
Also, some customers in desulfurization systems install non-metallic expansion joints in front of baffle doors, but forget to check whether the medium temperature is within the tolerance range of the skin. As we said earlier, the temperature of desulfurization flue gas is generally around 150℃, no problem. But if it is the flue gas temperature suddenly rising after the boiler MFT? Then you have to ask the design institute if they have considered the accident conditions. If not, it is recommended to install itDouble-sealed single-axis circular baffle doorOrElectric plug-in insulation doorTo isolate the high-temperature airflow.
After all, no matter how excellent the performance of non-metallic expansion joints is, they also have their "comfort zones". Low pressures, large displacements, corrosive media, rectangular or circular pipes – this is its home field. Don't use it as a panacea, and don't hesitate to use metal when it's time to use it. If you choose the right model, it can save you worry and money; Wrong selection, the rework cost is enough for you to buy three sets of metal.