Find out your working conditions first: How high is the temperature? How dirty is the dust? What's the pipeline going?
Don't search for models and compare prices as soon as you come up. It's similar to buying shoes with your eyes closed. To truly choose the rightExpansion joint of dust removal flueYou have to ask yourself three questions first.
First, how hot is the temperature?Don't just look at the design temperature on the nameplate, but look at the peak temperature during actual operation. Take a thermocouple to measure the temperature of the tube wall, or flip through the process parameter table. If it exceeds 400℃, then the ordinary rubber compensator (such as the one in our stationrubber compensatorOrRubber PTFE compensator) Basically can't bear it, so you have to lean on metal or non-metallic fabrics. If the temperature is below 200℃, non-metallic expansion joints (fabric fiber expansion joints) are more cost-effective and corrosion-resistant.
Second, how dirty is the dust?The dust in the dusting flue is no joke. If it is a cement plant type of high-hardness, high-wear dust, you should consider a model with a deflector, such asMetal rectangular expansion jointOrMetal Corrugated Expansion Joints in Cement Industry。 The deflector can direct the airflow to the center and avoid dust directly washing the bellows-this will be described later when installing. If that dust contain sulfur, acid and alkali, it is preferredNon-metallic expansion jointOrPTFE-lined hoseDon't use ordinary carbon steel cheaply.
Third, what is the pipeline going?Is it a straight pipe section or a turn? Is there any lateral displacement? For example, if you encounter an L-shaped or Z-shaped pipe that will cause lateral displacement when it expands thermally, it can't be solved by an axial expansion joint alone.Compound hinge transverse expansion jointOrCurved tube pressure balance expansion joint。 If the pipe is long and straight, thenUniversal corrugated expansion jointOrHigh temperature axial expansion jointYou can get it done.
There is no technical threshold for this step, just don't be lazy. Write down the three parameters of temperature, dust composition and pipeline direction diagram, and the later selection will be stable.
Choose the right type according to the working condition: metal or non-metal? Rectangular or circular? Do you want a flapper door?
The parameters are clear, and then we are in the right seat. I'll give you a comparison chart directly, and you can sieve it.
- Temperature ≤200℃, dust is not heavy, mainly to absorb axial displacement→ PreferredNon-metallic expansion joint (fabric fiber expansion joint), cheap, easy to install and corrosion resistant. Orrubber compensatorOkay, but be careful not to exceed the upper temperature limit.
- The temperature is 200~400 ℃, the dust is medium, and the pipe is rectangular→ Then onMetal rectangular expansion jointThis one in our station is specially designed for desulfurization of power plants and dust removal flue of steel plants. It has a guide tube and is wear-resistant and temperature-resistant. If the pipe is round, useCorrugated expansion joint for power station industryOrMetal Corrugated Expansion Joints in Cement Industry。
- Temperature exceeds 400°C, or need to withstand high pressure, vacuum→ Metal classes must be used. Such asHigh temperature axial expansion joint、External pressure single axial expansion joint, orStraight pipe pressure balanced expansion joint。 The vacuum pipe still needs to be usedSpecial hose for vacuumOrDouble hinge expansion joint for air-cooled island vacuum pipeline。
- Need to cut off the smoke or adjust the air volume→ Fitting next to the expansion jointFlue gas baffle doorOrRound Flap Door (Double Seal)。 Be careful not to get confused: the baffle door is for cutting off, not for absorbing displacement. If manual operation is required, useManual plug-in insulation door； To automatically control, useElectric plug-in insulation doorOrDouble-sealed single-axis circular baffle door。
Tsk, did you notice? Selection is actually a line: temperature determines the material, displacement determines the structure, and dust determines the protection measures. Don't be greedy to buy general-purpose expansion joints to deal with high-temperature dust, which is equivalent to laying mines in pipelines.
Preparation before installation: Don't reverse the direction of the guide tube arrow, and the tie rod nut must be removed to the designated position. How to calculate the pre-stretching amount?
After choosing, the goods have arrived, don't rush up. Do three things first, and any missing one may go wrong.
First, look at the direction of the arrow of the guide tube.Do you remember that we have a FAQ on our siteSpecific Function of Expansion Joint Guide Tube？ The arrows on the deflector must coincide with the direction of the pipeline media flow. Wherever the arrow is pointed, the bell mouth of the guide tube is pointed, the purpose is to let the airflow pass smoothly and avoid dust accumulation at the root of the bellows. If you install it backwards, if you accumulate too much dust, the expansion joint will quickly get stuck. I met a customer two days ago, installed the arrow backwards, and it was missed in three months. Do you think it was wrong?
Second, the adjustment nut on the pull rod must be removed to the designated position.We have them in our stationHow to adjust the tie rod nut of expansion jointThe Q&A. In order to prevent transportation deformation when the expansion joint leaves the factory, the nut on the tie rod is in a locked state. Before installation, you have to loosen the nut to leave the bellows at free length. But be careful not to overdo it-the tie rod itself is used to limit the position and prevent excessive stretching or compression. The specific amount of loosening depends on the product manual, usually allowing a margin for pre-stretching or pre-compression.
Third, how to calculate the amount of pre-stretch?Many newbies will ignore this. The hot pipe is installed at room temperature, you have to give the expansion joint a reverse initial displacement, wait for it to heat up just right back to the middle position. The calculation formula is not complicated: pre-stretching amount = (pipe thermal expansion ÷2). For example, if the pipeline is expected to expand by 20mm, then you will pre-pull the expansion joint by 10mm and then weld it. How to operate it? Use the tie rod nut against the nozzle, or use special tooling. Really can't count, just ask the technical customer service in our station and report your pipe, temperature and length, and they will help you calculate.
Formal installation: Don't die in the welding sequence, twist the flange bolts diagonally, and don't forget to leave a displacement allowance-my customers have stepped on these pits
With the preparations done, get hands on. The following details when installing, 90% of people will make mistakes.
Welding sequence: spot welding first, then symmetric welding.Don't weld it once, because the heat concentration will deform the bellows. Correct practice: Spot welding 4~6 points on the circumference first, and then jump welding in sections after cooling. ForMetal rectangular expansion jointBefore welding, it is best to polish the paint film on both sides of the weld, otherwise it will blister as soon as it is welded.
Flange bolts: must be screwed diagonally.Whether it is a round or rectangular flange, the bolts should be tightened gradually in the order of crossing, and the force should be applied in two to three times. Don't try to save trouble and finish it with the wind cannon, so the gasket will be unevenly stressed and 100% air leakage. By the way, don't change the bolt material randomly. Heat-resistant steel bolts have to be used in high temperature conditions, which will anneal at ordinary 8.8 high temperature.
Allow displacement margin: Don't let the expansion joint push to death.After installation, leave room for the limit nut on the tie rod. For example, if the expansion joint allows compression of 20mm and stretching of 10mm, then you adjust the limit nut to the free state, and then leave a margin of 2~3mm on each side to prevent accidental exceeding the limit. Otherwise, once the thermal expansion of the pipe exceeds expectations and the bellows is crushed to death directly, it will be replaced with a new one.
Don't use the expansion joint as a support.The pipe support should be welded, and the expansion joint should not bear the weight of the pipe. Especially vertically mountedLarge tie rod expansion jointThe tie rod only absorbs lateral displacement and cannot be lifted.
Debugging and inspection: How to test the pressure test? Is the displacement correct? What points should be reviewed after high temperature operation? -Giving you a self-test list
After installation, don't rush to put it into operation yet. Do a set of quick inspections, a matter of a few minutes, can save downtime in the next few days.
- Pressure test:Use 0.2~0.3MPa compressed air or nitrogen gas into the pipeline, and spray soapy water on the weld and flange surface of the expansion joint. Bubbling is leaking, hurry up repair welding or tighten bolts. Note that the test pressure should not exceed 1.5 times the design pressure, otherwise the bellows will bulge.
- Displacement check:Mark the relative positions of the pipes at each end of the expansion joint (e.g. by drawing a line on the pipe) and note the initial dimensions. Then let the pipe slightly move at room temperature (for example, pass some steam cooling water) to see if the expansion energy saver can't expand and contract freely. If it is stuck, it is mostly because the guide tube is installed backwards or the tie rod nut is not loose in place.
- Review after high temperature operation:After the pipeline heats up to the normal working temperature, stop the machine for cooling, and then check the appearance of the expansion joint. Focus on three points: First, whether there is obvious plastic deformation of the bellows (such as widening or narrowing of the corrugation spacing); Second, whether the guide tube has been worn down by dust (especially near the elbow); Third, whether the flange bolt is loose (the torque of the bolt will decrease after thermal expansion and contraction, so it needs to be re-tightened).
□ Pressure without leakage
□ The displacement direction is consistent with the design
□ Non-wear perforation of guide tube
□ Tie rod nut has movement allowance
□ Flange bolt torque up to standard
Making this list every three months works better than anything else.
Routine Maintenance: What to do if dust accumulates? Don't panic if you find an air leak. Judge whether to replace or repair it in three steps. How Long Does Expansion Energy Saving Last? Refer to the Lifespan Q&A in our site
If the equipment runs for a long time, there will be some minor problems. Don't call for a new one as soon as you find an air leak. Check it according to the following three steps.
Step 1: Look at the location of the air leak.If the leakage point is around the flange bolt hole, there is a high probability that the bolt is loose or the gasket has failed. Just re-tighten the bolts diagonally, or replace the metal-wound spacer. If the air leak spot is directly on the bellows (metal type) or fabric surface (non-metal type), then it is a little more troublesome.
Step 2: Judge the degree of damage.ForNon-metallic expansion jointIf only a small hole is worn out in the surface fiber layer, you can plug it with silicone rubber repair agent, and it will last for half a year. But if the multi-layer structure is broken, or the skeleton ring is broken, then it must be replaced. ForMetal rectangular expansion jointSmall cracks on the bellows can be repaired by argon arc welding, but first confirm whether the material matches (304 weld 304, 316L weld 316L). If there are more than two cracks, or the length exceeds 15% of the bellows circumference, don't repair them, just change them.
Step 3: Consider the dust accumulation problem.The easiest place to accumulate dust in the dust extraction flue is inside the expansion joint. Too much dust will limit displacement and accelerate corrosion. During routine maintenance, the inner cavity of the expansion joint should be purged with compressed air every three months, or the manhole should be opened for manual cleaning. If you pretendFlue gas baffle doorWhen the furnace is shut down for maintenance, close the baffle, then open the ash discharge port on the side of the expansion joint, and take out the ash with a shovel. Don't bother, I saw a customer deform the bellows because of dust accumulation, and finally the whole pipe was crooked.
As forService life of expansion jointWe have a special question and answer on our station. To be honest: there is no fixed number of years, it depends entirely on the working conditions. One setHigh temperature axial expansion jointIt is normal to work in a power plant for seven or eight years, but in dusty places in cement plants, you may have to replace the non-metallic parts in three or five years. The general principle is that metals have a design life of at least ten years and non-metals three to five years. However, the premise is that the type is selected correctly, the installation is standardized, and the maintenance is regular. If you do it all, it won't matter for ten or eight years.
Well, from selection to installation to maintenance, this set of processes go down, you encounter againExpansion joint of dust removal flueThe problem, I have the bottom in my heart. Again, don't buy randomly when you come up, report the parameters accurately, and match the baffle door when you need it. Don't save those few minutes of inspection time when installing. Only when the pipeline system is stable can your production be stable.