Find out why the flue needs "non-expansion joints" first-thermal expansion and contraction are no joke
Think about it, what's running in the flue? High temperature smoke, hundreds of degrees Celsius at every turn. When the pipe is heated, it will stretch, just like the railroad rails will arch in summer. If there is nothing to "digest" this stretch, the pipe junction is waiting to crack or deform the top of the bracket. What about that? Traditionally, metal corrugated expansion joints are used, but the flue has a characteristic-the flue often contains sulfides, dust, and corrosive condensate. In this environment, it doesn't take long for metal bellows to be corroded and perforated. So everyone slowly started using non-metallic expansion joints, which is what we often callNon-metallic compensator(fabric fiber expansion joint). It is not afraid of corrosion, it can also absorb multi-dimensional displacement, and the key cost is low. Doesn't that sound right?
Take it apart and see what parts of non-metallic expansion joints (fabric fiber expansion joints) are put together
You get a non-metal expansion joint, don't think it's just a piece of cloth. It's a "sandwich burger":
-outermost layer: Usually silicone-coated fiberglass cloth or fluorine tape, which is resistant to high temperatures, corrosion and waterproof.
-Intermediate layer: Thermal insulation cotton (aluminum silicate fiber cotton), block the heat and don't run out.
-inner layer: Temperature-resistant lining, direct contact with smoke, generally polytetrafluoroethylene or high silicon oxide cloth.
-frame: That is, the metal flanges at both ends, used to connect with the flue pipe.
-Strips and bolts: The fabric is laminated to the flange, and the seal is all dependent on it.
Some designs also add a guide tube (you can refer to our site aboutexpansion joint guide tubeQuestions and Answers), avoiding airflow directly washing the fabric. Tsk, even though it is not big, every floor has its job.
To put it bluntly, the principle is in one sentence: How does a flexible structure eat displacement
The principle of flue non-expansion joint sounds mysterious, but it is actually very simple:Use a soft fabric layer to "suck out" displacement from thermal expansion and contraction of the pipe。 For example, when the pipe is extended 10mm to the right, the fabric layer is compressed a little; When it shrinks to the left, the fabric layer stretches a little. It is okay to tilt up and down, left and right, and the fabric fibers can twist with it. Metal bellows can only absorb displacement by corrugation deformation, and its direction is limited; The whole surface of non-metal is soft, and it can move in three dimensions at will. And guess what? It also absorbs vibration at the same time, which metal pieces can't compare to. So to put it bluntly, it's a piece"Flexible wall" that can stretch, contract and bend。
Actual comparison: non-metallic expansion joint vs metal corrugated expansion joint, which should I choose for flue?
You'll definitely have to struggle with which one to choose. I'll tell you directly, don't hesitate:
-Flue operating condition: High temperature (below 300℃), corrosive gas, dust, selectNon-metallic expansion joint。 It is not afraid of acid corrosion, the price is cheap, and it is easy to install and disassemble. If it is broken, just change the fabric belt without moving the whole pipe.
-Metal corrugated expansion joint: Suitable for high temperature and high pressure steam pipelines and clean media, such as the main steam pipe of power stations, which must be used at this timeMetal corrugated expansion jointOur station hasCorrugated expansion joint for power station industryAndHigh temperature axial expansion joint）。 But on the flue? It leaks in half a year, and it can't be repaired.
If your flue temperature exceeds 600℃, you have to use special high-temperature resistant non-metallic materials, such as ceramic fibers. However, the general desulfurization flue temperature is 100-200℃, and ordinary silicone cloth is completely enough.
The easiest place to roll over during installation, explain it clearly to you at once
I've seen too many people install non-metallic expansion joints broken, and they blame the product quality back. In fact, there are a few key points:
- Don't reverse the direction: Some non-metallic compensators have a guide tube, which must be directed toward the smoke. If it is reversed, the airflow will directly wash the fabric and break in a few days.
- Pre-stretched or pre-compressed: During installation, according to the on-site temperature, artificially compress or stretch the expansion joint (see the manufacturer's manual for specific values), so that it is in the most comfortable state at the working temperature. Don't be lazy, saving this step is equivalent to laying a mine.
- The flange surface must be flat: The flue flange is deformed, and the non-metallic expansion joint is forcibly screwed on. As soon as the bolt is tight, the corners will leak. Check the flatness of the flange with a level ruler before installation, and grind it if it doesn't work.
- Bolt tightening should be twisted symmetrically in several times: Don't screw to death at once, screw to the specified torque in diagonal sequence 3-4 times. Otherwise, the pressure on the strip is uneven, and the seal will fail.
- Pay attention to heat preservation: The non-metallic expansion joint itself has an insulation layer, but when the external environmental temperature is low, it is recommended to add another layer of insulation on the outside to prevent condensate water from corroding the fabric.
Three things of daily maintenance can last for years if you follow them
- Look at the appearance: Is there any bulging, cracking, delamination? Especially the seams of fabric and flange, once peeling is found, quickly repair or replace new fabric bands. Don't wait for the air to leak.
- Check bolt torque: The flue operating temperature changes greatly, and the bolts will loosen when they expand and contract. It is recommended to check it quarterly with a torque wrench and re-tighten it at the initial value.
- Cleaning up dust: The surface of non-metallic expansion joint is prone to dust accumulation, especially the flue arranged horizontally. Too much dust can add weight and may corrode the fabric. Clean with compressed air or clean with a soft brush. Don't scrape with hard objects.
Do these three steps well, and it is the norm for non-metallic compensators to be used for three to five years. If you encounter special circumstances (such as smoke containing a lot of oil), you have to shorten the inspection cycle.
We still have one in our stationRectangular non-metallic expansion joint、Desulfurization flue gas baffle doorThese supporting products can be considered together if they encounter flue system modification. The principle of flue non-expansion joint is not complicated to put it bluntly, but every step of selection, installation and maintenance can't be careless. If you follow the steps above, you won't fall into the pit.