Find out how "ruthless" your flue is first-don't leak in temperature, corrosion and pressure
What are you most afraid of when choosing flue expansion joint? Afraid that you didn't even figure out the temper of your own flue, you ran to ask the boss "which one is durable". The boss recommends the most expensive one to you, and you may use it for half a year; I recommend you cheap ones, but I'm afraid of bursting tubes. Which is durable? The answer is not in the mouth of the manufacturer, but in your working condition data.
So the first step, instead of looking for products, look for these three numbers first:
- Maximum temperature: How many degrees during normal operation? Is there an instant overheat? For example, the flue of cement kiln can reach 600℃ or even higher, so don't think about rubber, and lean directly on the metal.
- Media composition: Is there SO₂, H₂S, Cl⁻¹ in the flue gas? The flue gas after wet desulfurization has high humidity and strong acidity, which can not be carried by ordinary stainless steel, so it has to be lined with PTFE or directly applied to non-metal.
- Working pressure: Positive or negative pressure? Are the pressure fluctuations large? The pipe pressure behind the induced draft fan in a power plant is generally not high, but if it is the boiler outlet, it may be several kPa or even higher.
Can't get accurate data? Check the historical curve of DCS, or measure it one by one with a thermometer or thickness gauge on the spot. Don't guess, guessing is wasting money.
Three kinds of mainstream flue expansion joint disassembly ratio: metal corrugation, non-metal fabric, rubber compensator, who is more manufactured?
Okay, now you have three numbers in your hand. Let's compare the three most common expansion joints on the market-don't just look at advertisements, but look at "internal strength".
1. Metal corrugated expansion joint
This thing is stainless steel bellows, which is thick, pressure-resistant and high-temperature resistant. You see that "corrugated expansion joint for power station industry", "metal corrugated expansion joint for cement industry" and "high-temperature axial expansion joint" all belong to this category. It can carry more than 600℃ (even higher after adding insulation layer), and the pressure can reach several MPa. What about the disadvantages? It cannot absorb too much lateral displacement and is afraid of corrosion. There are chloride ions in the smoke? 304 stainless steel pits quickly, so it has to be upgraded to 316L or duplex steel, and the cost is going up.
2. Non-metallic expansion joint (fabric fiber expansion joint)
Also called non-metallic compensator, the main body is soft materials such as silicone cloth, fluororubber and glass fiber. Its biggest advantage is its displacement compensation ability-it can eat in axial, transverse and angular directions, and it is corrosion resistant and vibration absorbing well. For example, "rectangular non-metallic expansion joint" is especially used in desulfurization flue. However, note that the pressure resistance is limited, generally no more than 0.1MPa, and the temperature depends on the specific fabric. Ordinary silicone cloth is about 250℃, and fluororubber can reach the beginning of 300℃. If your working condition is high temperature and high pressure, it can't bear it.
3. Rubber compensator
Cheap, easy to install, first-class rod for vibration isolation. Rubber compensator or rubber PTFE compensator is suitable for pipelines with low pressure, low temperature (generally
And guess what? Two days ago, I met a customer who insisted on using a rubber compensator at the outlet of the desulfurization tower. As a result, it leaked in three months-the temperature was not high but the acidity was really strong. Later, the non-metallic expansion joint was replaced, and it was stable.
Seat according to working conditions: select metal at high temperature and high pressure, select non-metal after corrosion and large displacement, select rubber for vibration isolation and save money
Now you know what you know? To apply this formula directly:
- Temperature> 300 ℃, pressure> 0.1 MPa→ Metal corrugated expansion joint. The specific model depends on the working conditions: "Universal corrugated expansion joint" is selected for axial displacement; Select "high-temperature axial expansion joint" for particularly high temperature; Choose "Metal Rectangular Expansion Joint" for large-diameter rectangular flue.
- Temperature → Non-metallic expansion joints. In particular, the flue after wet desulfurization must use "rectangular non-metallic expansion joint" or "non-metallic expansion joint (fabric fiber expansion joint)", which is acid-resistant and water vapor-resistant.
- Temperature → Rubber compensator. For example, the outlet of induced draft fan is soft connected, and it is cost-effective to use "rubber compensator" or "rubber PTFE compensator".
Note that this is only an approximate demarcation. If the working condition is high temperature with corrosion? Then line with PTFE hose, or add anti-corrosion coating inside the metal corrugated expansion joint. Don't be stubborn.
Installation and maintenance Don't step on pits: the guide tube is installed backwards, the tie rod is not removed, and the baffle door is not installed-these things you must pay attention to
I bought the right thing, the installation was a mess, and it broke within a few days of use. You have to keep an eye out.
The guide tube is in reverse direction
The function of the expansion joint guide tube is to guide the flow direction of the medium and protect the bellows from being washed. But the direction of the arrow is critical-it must follow the direction of the medium. Install backwards? The deflector is a direct ride, and the bellows are cut by high-speed flue gas and perforated in a few months. How to confirm? Look at the arrows on the barrel, or look up the drawings.
The tie rod nut is not loosened
Transporting a tie rod and adjusting a tie rod are two different things. Many expansion joints leave the factory with transport rods (or locking nuts) to prevent deformation during transportation. The transport tie rod must be removed after installation, otherwise the expansion joint will not be able to expand and contract freely. The function of the expansion joint tie rod is to limit the position, not to lock it. Some buddies forgot to dismantle them, and as a result, the pipeline expanded thermally, which directly broke the expansion joint. Alas, this is a waste of money.
No baffle door installed or isolation not in place
In the flue that needs to be overhauled, be sure to be equipped with flue gas baffle door or circular baffle door. Otherwise, once you want to shut down the furnace to replace the expansion joint, you have to wait for the whole system to cool down and empty, and the construction period will be delayed for several days. Install electric plug-in type insulation door or double-seal single-axis circular baffle door in advance, and you can isolate online, saving time and effort.
Before installation, find out the problem that the screw of the expansion joint needs to be disassembled-disassemble the transportation tie rod, and retain the adjustment tie rod according to the design. If you don't understand, just read the instructions. Don't think about it yourself.
Finally calculate the account: Don't just look at the price, life time × safety is really cost-effective
Okay, now you know how to choose and install. But many people can't pass this last level-looking at the quotation list, they think that what is cheap is a good deal. Think about it, a rubber compensator costs two hundred yuan, and its life span is one year; A non-metallic expansion joint costs two thousand yuan and has a lifespan of five years. Which is a good deal? Not that I didn't know, but I was shocked when I calculated.
More critical is security. If the flue expansion joint explodes, the high-temperature smoke is sprayed out, which will stop production at the light and hurt people at the worst. Do you dare to bet on a bargain?
Make a table of total cost of ownership. Include the purchase price of expansion joint, installation fee, maintenance fee, life expectancy and downtime loss. For example, although the metal corrugated expansion joint is expensive, it can last for 8-10 years under high temperature conditions. Non-metallic expansion joints are cheap but short-lived, and rubber compensators have to be replaced in one or two years. Add in the labor and shutdown losses for each replacement…and you get the idea.
You asked "which flue expansion joint is durable"? There is no standard answer, only the answer that best suits your working conditions. Follow these 3 steps-find out the working conditions, choose the right type, install the right pit-every penny you spend is on the edge of the knife. Spending less money is truly durable.