Step 1: Find out what's going on in your flue first-temperature, pressure, displacement, none less
To be honest, I have seen too many people ask "Give me an expansion joint" as soon as they come up, and they don't even say what the working conditions of the flue are. As a result, within two months of buying and installing it, the bellows cracked, the flange leaked, and it was ripped and reworked. Alas, why bother?
When you design a flue expansion joint, the first thing you do is not to look through the selection manual, but to find out these three numbers first:
- Temperature: What is the highest degree? Is it persistent heat or hot and cold? For example, the temperature of the flue of a power station boiler can soar to five or six hundred degrees.Universal corrugated expansion jointI can't handle it, I have toHigh temperature axial expansion joint or insulated.
Tip: If there are corrosive components in the flue gas, such as wet flue gas after desulfurization, you have to consider itPTFE-lined hoseOrPTFE compensator。 - pressure: Positive or negative pressure? Are the pressure fluctuations large? Some flues are slightly negative pressure, just choose a non-metallic one; However, if the positive pressure at the outlet of the fan is more than 0.1MPa, it is necessary to honestly use metal corrugation.
- displacement: Which direction does the pipeline run? Horizontal, vertical or angular displacement? How big is the quantity? It is not enough for you to know "thermal expansion and contraction", you have to calculate the specific value. For example, a 30-meter-long carbon steel flue, with a temperature rise of 300℃, has an elongation of about 110mm. If the expansion joint you bought can only absorb 50mm, it is not an expansion joint, but a "frustration joint".
These three data are not accurate, and the back is all blind. So the first step is to honestly find a design institute or calculate it yourself, and don't be lazy.
Step 2: Don't be blind in the selection, metal or non-metal? Rectangular or circular? Compare these situations and select
The data is in hand, so how to choose? I'll give you a practical comparison table directly, and you can check it yourself:
- High temperature, high pressure, large diameter(For example, the main flue of the power station): SelectMetal corrugated expansion joint, the specific model depends on the displacement direction.
-Large axial displacement? useStraight pipe pressure balanced expansion joint orExternal pressure single type axial type expansion joint.
-Large lateral displacement?Compound hinge transverse type expansion joint orThe pressure balance type expansion joint of curved tube is arranged. - Rectangular flue(For example, the import and export of desulfurization tower): Don't be entangled, directly chooseMetal rectangular expansion joints orRectangular non-metallic expansion joint. The advantages of non-metal are that it is not afraid of corrosion, sound absorption and vibration reduction, but its pressure bearing capacity is weak, which depends on the working conditions.
- Corrosive media(Flue gas after wet desulfurization): preferrednon-metallic expansion joints (fabric fiber expansion joints), ora rubber compensator,Rubber PTFE Compensator. The corrosion of metals is not as worry-free as non-metals.
- Space is constrained and needs to absorb a variety of displacements:Double straight pipe bypass pressure balance type expansion joint orRotating compensators can save lives sometimes.
Have you noticed? Selection is not about patting the head, but talking by looking at the data. Two days ago, a customer insisted on taking itSleeve-type pipe expansion joints are used in high-temperature and high-pressure steam pipes. I tried to persuade them for a long time-the risk of air leakage is high, so I finally replaced themThe high-temperature axial expansion joint has been used for three years without any problems.
Step 3: Calculate the expansion amount, and don't let the expansion joint become a "choking joint"-how to check the displacement absorption capacity
Placing an order after the selection? Don't worry, there is still a big pit: Can the expansion joint you bought absorb the displacement you calculated?
Each expansion joint has a rated compensation amount, such as aGeneral-purpose corrugated expansion joint, the manufacturer indicates that the axial compensation amount is ±50mm. But you should pay attention, is this a single wave or a multi-wave? Did you hit the temperature correction factor? What about the pressure correction factor?
Actual allowable compensation = rated compensation × temperature correction coefficient × pressure correction coefficient × fatigue life coefficient
(Don't ask me what the specific coefficient is, each manufacturer gives different, you have to ask clearly. However, most manufacturers provideModel and size of expansion jointTable, it will be clearly written in it.)
You calculated that the axial extension of the flue was 120mm, and you bought an expansion joint with a rated compensation amount of 100mm. Does it seem enough? However, the temperature correction coefficient is 0.8, the pressure correction coefficient is 0.9, and it is only 72mm after multiplying. And guess what? After installing it for a month, the bellows cracked. So,Be sure to multiply by the correction factor after calculationRather bigger than stuck with the upper limit.
Step 4: Confirm the guide tube and pull rod before installation. If this step is reversed, it will be scrapped directly
This is the hardest hit by rollovers. Many masters think that the expansion joint can be welded. As a result, the beltThe guide tube is installed in the opposite direction, and the flue gas directly washes the bellows, which will perforate in a few months. The function of the guide tube is to protect the bellows, and the direction of its arrow must point to the flow direction of the medium. If you install it backwards, it is equivalent to not installing it.
Additionally, withThe expansion joint of the tie rod (e.g.A tie rod of a universal corrugated expansion joint,Large tie rod expansion joint), the tie rod nut is adjusted and pre-deformed during installation, so don't screw it randomly. If you find that the length of the expansion joint is longer than the actual installation distance before installation, it is the pre-stretching amount reserved by the manufacturer. You have to adjust the tie rod nut to the proper compression position before installing it. After installation, do you want to remove the tie rod nut? Sub-situation: If it is subject to internal pressure, the tie rod is a structural part and cannot be disassembled; If it is a temporary tie rod for transportation, it must be removed. How to judge? Read the product manual, or ask the manufacturer directly. Don't take it for granted.
And one more thing,Do you need to remove the screw of the expansion joint？ As mentioned earlier, see if it is a transport screw or a working tie rod. If you remove the working tie rod, as soon as the pipe is heated, the bellows will be pulled off directly, and the consequences will be made up by yourself.
Step 5: Don't forget the matching baffle doors and insulation doors. They are partners with the expansion joints, not passers-by
A lot of people just stare at the expansion joint, forgetting that there are still a bunch of "good buddies" in the flue system. Such asFlue gas baffle door,Round baffle door (double seal),Double-sealed single-axis circular baffle door,Single axle double flapper doors and more. The function of these doors is to cut off or adjust the smoke. If your expansion joint doesn't cooperate well with the baffle door, the smoke will rush over during maintenance. Who can stand it?
For example, the inlet and outlet of the desulfurization system are usually installed on one sideDesulfurization flue gas baffle door, installed on the other sideElectric plug-in insulation door orManual plug-in type insulation door, with middle fittingNon-metallic expansion joints. In this way, the door is closed during maintenance, and the expansion joint is not stressed and easy to replace. If you install the expansion joint instead of the baffle door, the expansion joint is a "disposable consumable"-if it breaks, you have to stop the whole system before you can replace it.
Also, pay attention to distinguishingThe difference between electric butterfly valve and baffle door: the sealing performance of butterfly valve is not as good as that of double-sealed baffle door, and it is easy to leak when used in smoke isolation. Don't use butterfly valves instead of insulating doors cheaply.
Step 6: Write at the end-common rollover scenes and remedies, and spend less money after reading
After working for more than ten years, I can publish a book on the rollover scene I have seen. Today, pick three of the most common ones, and you compare them to avoid pits:
Rollover 1: The expansion excerpt is too small to fit.
Reason: Installation tolerances are not considered, and the actual flue spacing is larger or smaller than the design. Remedy: Buy the beltThe expansion joint of the tie rod can be fine-tuned by adjusting the tie rod nut. If the gap is too big, you can only return to the factory.
Rollover 2: Corrugated pipe corrosion perforation.
Reason: Media corrosivity was neglected during model selection. For example, desulfurized wet flue gas, use ordinaryThe metal hose certainly won't hold it. Remedy: Replace withPTFE-lined hoses orPTFE compensator, or withNon-metallic expansion joint (fabric fiber expansion joint). If it has been installed, it can only be shut down and replaced. You feel bad about the money, right?
Rollover 3: Expansion joint vibration abnormal noise.
Reason: Flue flow rate is too high, or expansion joint stiffness does not match. Remediation: Additional installationVacuum special hoses orRubber compensator to dampen vibration. If it is a large pipeline, considerAir-cooled island vacuum pipe double hinge expansion joint This structure specifically responds to vibration.
When designing flue expansion joints, don't just look at the product itself, but also consider the whole pipeline system as a whole. Temperature, pressure, displacement, corrosion, installation, accessories, which ring problems have to be reworked. If you are unsure, contact our team directly, we provideModel and size of expansion jointTable, and can also help you calculate the compensation amount, saving you messing around. After all, if you spend money on experience, do as little as you can.