Two days ago, I met a customer, and as soon as I came up, I asked: What is the use of flue expansion joint in power plant? His new unit was commissioned, and the air leakage at the flue interface was terrible. He looked for several companies but couldn't figure it out. Tsk, in fact, this thing is complicated and simple — you just think of it as a "joint" of the flue, specifically dealing with thermal expansion, contraction, vibration and displacement. Today, let's go through it from the beginning, from selection to installation to maintenance, you can just do it.
Step 1: Find out what the flue expansion joint does in the power plant
The temperature in the flue of the power plant is always hundreds of degrees Celsius, and the steel pipe will stretch when heated, and then retract when cooled. This amount of expansion and contraction is quite a lot, and the flue tens of meters long can be different by several centimeters. If it is hard pressed, the flange will deform at least, and the pipe will crack at worst. What about that? That's what expansion joints do. It not only absorbs axial expansion and contraction, but also can carry lateral displacement and angular displacement. For example, when the boiler is started or shut down, the whole flue is shifting; For example, the low-frequency vibration caused by the operation of the fan can also be buffered by the expansion joint. To put it bluntly,Function of flue expansion joint in power plantIt is to "soften" the rigid pipeline system, so that thermal expansion and contraction, mechanical vibration and installation deviation will not damage the pipeline structure.
The operating conditions of flue in different locations are much different. The flue gas at the boiler outlet is high in temperature and ash, and the wet flue gas at the desulfurization section is highly corrosive. You have to find out the actual parameters on the site before selecting the type.
Step 2: Choose the right products according to different locations of the power plant
When it comes to model selection, you must not try to save trouble. Let me give you a few practical matching ideas:
- Boiler outlet to economizer, air preheater section: High temperature (above 400 DEG C), large pressure fluctuation, usingNon-metallic expansion joints (fabric fiber expansion joints)OrHigh temperature axial expansion joint。 Non-metal has high temperature resistance, large compensation, can absorb multi-directional displacement, and is light in weight, and has low pressure on pipeline supports and hangers.
- Inlet and outlet flue of desulfurization absorption tower: Wet flue gas contains sulfur and corrosion is serious. Don't use ordinary metal at this time. recommendDesulfurization flue gas baffle doorCooperateNon-metallic expansion joint。 And guess what? The fluororubber or polytetrafluoroethylene layer of non-metallic expansion joint can resist acid corrosion, and the baffle door is used to isolate smoke during maintenance. You can also considerPTFE compensatorSpecialized in dealing with strong corrosive media.
- Front and rear of dust collector, inlet and outlet of induced draft fan: Here there are many vibrations and displacements, usingMetal rectangular expansion jointOrUniversal corrugated expansion jointHigh structural strength, matchingFlue gas baffle doorIn use, it is cut off during maintenance for convenient operation.
- Air-cooled island vacuum pipe: make no mistake, it has to be usedDouble hinge expansion joint of air-cooled island vacuum pipeOrCompound hinge transverse expansion jointSpecially absorb the angular displacement of the pipe system, and the sealing requirements are extremely high.
If the pipeline needs to be cleaned or switched regularly, it can be equipped withElectric plug-in insulation doorOrManual plug-in insulation doorAnd the expansion joint is installed in series. For example, in our stationSingle-axis double-flapper doorAndDouble-sealed single-axis circular baffle doorThe sealing effect is lever.
Step 3: Check These 5 Key Points Before Installation
Many customers plant in the installation process. When the goods arrived, the installation team went directly up, but it was leaked within two months. Remember, check at least these five points before installation, and don't omit one thing:
- Guide tube orientation: The guide tube should be directed toward the flow direction of the medium, otherwise the airflow will directly scour the corrugation or fabric, and the life will be immediately discounted. Regarding the specific function of the diversion tube, we have a special question and answer on our station, you can go and flip through it.
- Tie rod nut preloaded state: The tie rod nut is tightened during transportation to protect the expansion joint from deformation. Must be loosened to the design position before installation, never forget. How to adjust it specifically? Refer to the question and answer of "How to adjust the expansion joint tie rod nut" in our station.
- Arrow Direction: The arrow on the expansion joint generally points to the direction of media flow (also the direction of displacement). If it is installed backwards, the compensation ability will be completely messed up, and in serious cases, it will be directly broken. You can see the answer of "What is the direction of the arrow of the expansion joint" in our station.
- Coaxiality of pipe at both ends: Flue flanges and unevenness? Adjust with the spacer, do not firmly pull the expansion joint in place. Otherwise, the bellows or fabric ring is unevenly stressed and will crack within a few days.
- Pre-stretching/pre-compression: Some working conditions need to be pre-displaced according to the installation temperature. For example, if it is installed in winter, the pipe will be thermally elongated in the future, so it is necessary to pre-stretch the expansion joint for a certain distance. This numerical technical protocol usually says that the installation team must understand the drawings.
There is also a special requirement for the installation of non-metallic expansion joints-the fabric ring cannot be twisted, otherwise the seal will fail. When installing, use special spreaders, don't use wire rope directly.
Step 4: How to check and accept after installing it? Three-step test method
Don't rush to seal the wall after installation. Take three steps for acceptance:
First step, visual inspection: Look at the expansion joint for obvious deformation, scratches and bulging. Is the deflector centered? Is the tie rod loose?
Second step, weld/flange tightness test: Brush the welds and flange joints at both ends of the expansion joint with soapy water or leak detection liquid, and pass low-pressure air (0.1~0.2MPa) to see if it is bubbling. No foaming is considered to be sealed qualified. If it is a metal expansion joint, you can also do a hydraulic test, beat according to 1.5 times the design pressure, and hold the pressure for 10 minutes.
The third step, displacement compensation test: If conditions permit, simulate the thermal displacement of the flue-apply axial and transverse displacement to the expansion joint with a jack or hoist to see whether it can freely expand and contract into place and whether there is any residual deformation after returning to position. This step can find the problem of insufficient design margin in advance.
The acceptance record should be kept well, and it should be used for comparison in future maintenance.
Step 5: Don't be lazy in routine maintenance
Many power plants feel that the expansion joint is installed once and for all, but it has to be replaced in less than three years. If you listen to these actions, you can live an extra three years:
- Look at wear: Is there any fluff or hole in the fabric layer of the non-metallic expansion joint? Are there any wear marks on the crest of the metal expansion joint? In particular, the bellows downstream of the guide tube is easily worn by the particles entrained by the air flow. Check once a half year, and if early damage is found, glue or patch tablet will be applied.
- Check for leaks: Use infrared thermal imaging camera or hand feel, find local temperature abnormality or steam, quickly check. The leakage point is often the tie rod hole and flange bolt, which can be alleviated by tightening it for one turn.
- screw bolt: Thermal expansion and contraction after operation will loosen the flange bolts. When shutting down for maintenance, screw all the bolts again according to torque, especially for large diameter flanges. Don't forget to check whether the tie rod nut is loose due to vibration-we have a question and answer on "Does the screw of the expansion joint need to be removed", which specifically talks about the difference between the transportation screw and the installation screw.
- Anti-corrosion: In the flue of desulfurization section, ash accumulation and scale on the surface of the expansion joint should be cleaned regularly in a humid environment to prevent chemical corrosion. If the outer coating of the metal expansion joint falls off, it should be repaired with temperature-resistant and anticorrosive coating in time.
Different brands of expansion joints have different maintenance cycles. You better set up an equipment ledger to record the model, installation date and inspection results of each expansion joint. For example, this site'sCorrugated expansion joint for power station industryOrMetal Corrugated Expansion Joints in Cement IndustryThey all have their own instructions for use, so don't lose them.
Okay, from model selection to installation to maintenance, I've said everything I need to say. If you have a power plant renovation project in your hand, why don't you go through this list directly? I promise you won't step on a big pit. If you need specific model parameters, feel free to turn over the product information in our station — —Metal hose、PTFE-lined hose、rubber compensator、Rotary compensator、Sleeve type pipe expansion joint…Everything you need, you can choose it yourself.