Find out first: What role does the flue expansion joint play in the pipeline?
Seriously, who of us plumbing people has not been tricked by "thermal expansion and cold contraction"? As soon as the flue heats up, the steel pipe suddenly stretches, and the interface clicks, which may directly damage the fan and crack the support. At this moment, the flue expansion joint is the "flexible and stretchable" joint-it specializes in holding up all the displacement, vibration, and air leakage caused by the pipe itself.
To put it bluntly, its core roles are three:Absorbing displacement, isolating vibration and noise, ensuring seal。 But knowing these three points is useless, you have to know exactly how to use it to solve the current troubles. The following moves are all made in actual combat. Just follow them after reading them.
First trick: Use it to absorb heat displacement, and don't let the pipe "stretch" to damage the equipment
Pipes, this thing, "stretch" as soon as the temperature rises. You have to calculate an account: a one-meter-long carbon steel flue can be elongated by 1.2mm when the temperature rises by 100℃. If the flue is tens of meters long and heats up to three or four hundred degrees, the displacement can add to more than 10 centimeters. Hard pushing? The flange bolt is broken, the bracket is deformed, and the fan bearing is displaced-a repair is less than tens of thousands of dollars.
What about that? In series in the middle of the flueexpansion jointAnd let it "eat" these displacements. Remember two hard indicators when selecting a model:
- The displacement amount should be left with a margin: Calculate the total elongation according to the length of the pipeline, the medium temperature and the temperature difference of the installation environment, and multiply it by the safety factor of 1.2. For example, to calculate the displacement of 80mm, you should choose at least the model that can compensate 100mm. From our stationUniversal corrugated expansion joint、High temperature axial expansion jointThe axial compensation capacity ranges from tens of millimeters to hundreds of millimeters, and it can be selected according to the working condition parameters.
- Don't just look at the axis: The flue pipeline is often turned and misaligned, and may have lateral displacement or angular displacement. That's when you have to use itCompound hinge transverse expansion jointOrCurved tube pressure balance expansion jointThey can absorb displacements in multiple directions at the same time, preventing the pipeline from "stopping".
Tip: Be sure to loosen the tie rod nut on the expansion joint before installation-the nut is screwed out at the factory for transportation. If it is not loosened, the expansion joint is equal to a steel pipe, and it can't compensate for the displacement at all**. How to tune it? Article 12 of FAQ has detailed steps. Simply put, it is: first screw the locking nuts at both ends to a free state, so that the bellows can expand and contract freely, and then screw them until the scale marks are aligned.
Trick 2: Use it to withstand vibration and noise, and spend a small amount to save big maintenance
Alas, the vibration in the flue, can you stand it? When the fan was turned on, the whole pipe shook, and the noise made my ears hurt. Vibration is not only noisy, but also makes the weld fatigue crack and the instrument circuit fall off. And guess what? Many times changing the expansion joint can solve it.
- Low frequency and large amplitude vibration(For example, fan start-stop, pipeline resonance): UseNon-metallic expansion joints (fabric fiber expansion joints)Orrubber compensator。 This kind of product itself is soft, can absorb more than half of the vibration energy, and it is light in weight and has little impact on the bracket. Note-if the flue temperature exceeds 150℃, don't use rubber, choose fabric fiber.
- High frequency small amplitude vibration(such as airflow pulsation, valve disturbance): UseMetal hoseOrCorrugated expansion joint, their stainless steel bellows have a natural damping effect on high frequency vibrations. If space is limited, selectSpecial hose for vacuumWhich is voltage-resistant and vibration-isolated.
Don't underestimate this investment. A set of rubber compensators are hundreds of pieces, but it can save thousands of pieces for replacing fan bearings every year. Is that the truth?
The third trick: rely on it to ensure that the flue is sealed, and there is no smoke and no air leakage
How annoying is a flue leak? It ranges from smoke backward corrosion equipment to pulverized coal explosion (don't laugh, something really happened). If the expansion joint is not sealed well, the environmental monitoring of the whole system will not pass.
- Flue gas temperature below 200℃Preferred selectionNon-metallic expansion jointOrRubber PTFE compensator。 The non-metal laminated structure comes with its own sealing gasket. When installing, the flange surface is cleaned and the bolts are symmetrically tightened (from the middle to both sides, twisted in three times).
- Flue gas temperature 200~600℃: Metal expansion joints must be used, such asCorrugated expansion joint for power station industryOrMetal Corrugated Expansion Joints in Cement Industry。 Pay attention to matchingguide tube(See Article 7 of Q&A for details). The guide tube can guide the high-temperature flue gas into the bellows, avoid direct erosion of the weld, and reduce the wear and corrosion of the bellows by the medium. During installation, the direction of the arrow of the guide tube must be consistent with the flow direction of the medium-reverse arrow equals white installation.
- Corrosive flue gas(Desulfurization, chemical): UsePTFE-lined hoseOrPTFE compensator。 PTFE lining is acid and alkali resistant, but no sharp objects can scratch the lining during installation, and the torque of flange bolts should be uniform to prevent extrusion deformation.
The seal is done, which not only meets the environmental protection standard, but also saves the maintenance fee of leakage repair. Tsk, this is a good deal.
The fourth trick: match the smoke baffle door to achieve more worry-free maintenance and isolation
The biggest headache of a flue system is overhaul-you can't stop the entire flue, can you? That's when you needFlue gas baffle doorTo help. The expansion joint is responsible for absorbing the displacement, and the baffle door is responsible for cutting off the smoke. When the two are matched, the inspection port can be opened as soon as you want.
- Maintenance isolation scenario: Install one upstream or downstream of the expansion jointDouble-sealed single-axis circular baffle doorOrSingle-axis double-flapper door。 This kind of door has two sealing surfaces after closing, and the air leakage rate is less than 1%. Maintenance personnel can work directly inside the pipeline.
- Long-term downtime scenarios: withManual plug-in insulation doorOrElectric plug-in insulation doorThe plug-in board completely seals the pipeline to ensure that the smoke will not flow back. Note-The sealing surface of the plug-in door should be cleaned regularly for dust accumulation, otherwise it will not be closed tightly.
- Desulfurization flue environment: must be used withDesulfurization flue gas baffle door, its blades and sealing materials are resistant to acid and alkali corrosion. I have customers who didn't use it right, and the baffle door rust out in half a year. Alas, it's too late to regret it.
Note during installation: Leave a straight pipe section of at least 200mm between the baffle door and the expansion joint to prevent the impact force generated by the opening and closing of the baffle directly acting on the bellows.
Final step: Select the right model according to the working condition, and remember these 3 checkpoints before installation
Just knowing the function is not enough, choosing the wrong model is equivalent to busy work for nothing. You go through the following three checkpoints, and there is basically no error:
Point 1: Look at the medium temperature and pressure
Temperature> 400℃ or pressure> 0.1MPa, honest and practical High temperature axial expansion jointOrExternal pressure single axial expansion joint。 Low temperature and low pressure section,Non-metallic expansion jointLower costs.
Point 2: Look at pipe diameter and connection method
Large diameter flues (> 1 m in diameter) must be used Metal rectangular expansion jointOrRectangular non-metallic expansion jointThe circular tube is usedUniversal corrugated expansion joint。 The connection mode is preferably flange connection-convenient to disassemble and assemble, and the expansion joint body can be directly changed during maintenance. If the pipe is welded, then use the welded end pipe, but the bellows should be wrapped before welding to prevent slag splashing.
Point 3: Look at the installation direction and spacing
There is an arrow on the expansion joint-that is the medium flow sign (see question and answer#10), and it must be followed. When multiple expansion joints are connected in series, a fixed bracket should be added in the middle, and the distance should not exceed 20 meters. The sliding clearance should be reserved for the base of the bracket, and do not weld it to death.
After the expansion joint is installed, don't forget to remove the shipping screw (Q&A#14), which will lock the expansion joint unless you specifically need it. The removed screw is put away, and it can be used as a backup in case of later replacement.
Well, if you go through all these tricks, the flue system is guaranteed to behave like a cat- -no stretching, no shaking, no air leaking. If you are unsure of the specific model, feel free to flip through the product page of our station, compare the parameters, and it will be settled soon.