Step 1: Find out the temper of your flue-temperature, pressure, and medium are all necessary
Before choosing a flue corrugated expansion joint, you have to find out the "temper" of the pipe. What's the temperature? How stressful? Are smoke, steam or corrosive gases running inside? These parameters directly determine which type of expansion joint you should use.
Two days ago, I met a customer, and when he came up, he asked, "Give me a universal expansion joint, as long as it can be installed in the flue." As soon as I heard it, I knew that something bad was going to happen-the working conditions of the flue were hugely different, and the desulfurization flue of power plants and the flue of cement kilns were completely different. If you think the same, there is a high probability that it will not take long to leak when you buy it back.
How to find out exactly?Take a piece of paper and write it down:
- Maximum operating temperature:Is it normal temperature, 200℃, 400℃ or above 800℃? This determines whether to use a regular metal bellows orHigh temperature axial expansion joint(This site has a special high temperature series).
- Working pressure:Positive or negative pressure? Most flues are slightly positive or negative pressure, but some dust collectors have large pressure fluctuations at the inlet and outlet, so special attention should be paid to them.
- Media composition:Are there sulfides and chloride ions? If there is corrosion,PTFE compensatorOrPTFE-lined hoseMight be more appropriate.
- Displacement Type:Is the pipe axially telescopic? Swing laterally? Or angular displacement? Different displacements correspond to different structures-for axial displacementUniversal corrugated expansion jointOrExternal pressure single axial expansion joint； For large lateral displacementCompound hinge transverse expansion joint； For complex combinationsStraight pipe pressure balanced expansion joint。
Write these data clearly, and the later selection will not deviate.
Step 2: Seat-pick out the most appropriate expansion joint type from the products of this site
After figuring out the working conditions, it is time for you to go to the product library and "take a seat". The product line on our site is very complete, but you have to choose according to the scenario:
- Boiler flue and desulfurization system of power station:Look firstCorrugated expansion joint for power station industryAndDesulfurization flue gas baffle doorMatching expansion joint. High temperature, low pressure, corrosion, recommendedMetal rectangular expansion jointOrNon-metallic expansion joint (fabric fiber expansion joint)。
- Kiln head and kiln tail in cement industry:The temperature is always five or six hundred ℃ or even higher, and it must be upMetal Corrugated Expansion Joints in Cement Industry, orHigh temperature axial expansion joint 。 Don't buy the general-purpose type cheaply, you can't bear it.
- Need a large amount of compensation and fear of thrust:useCompound straight pipe bypass pressure balanced expansion jointOrCurved tube pressure balance expansion jointThey can balance the pressure by themselves and reduce the thrust on the pipe frame.
- Space constrained, lateral displacement only:chooseCompound hinge transverse expansion jointOrRotary compensator。
- Buried pipeline:haveDirect buried (fully buried) type expansion joint, specially designed for underground working conditions.
Don't be too troubled, compare the following table (in fact, there is one principle: the more severe the working conditions, the more special type should be selected).
Step 3: Don't just look at the model, these parameters are the key-how to determine the diameter, wavenumber and compensation amount
Many people choose expansion joints only by looking at the model, thinking that "if the model is right, it can be installed". Tsk, so wrong. The same model has different paths, wavenumbers and compensation amounts, and the performance is very different.
Diameter (DN): Is the nominal diameter of the expansion joint, which must be consistent with the inner diameter of the pipe. If it is too large or too small, there will be problems-if it is too small, the resistance will be large, and if it is too large, the connection will easily leak. Measure the inner diameter of the pipe before you buy it, don't estimate it.
wavenumber: The number of corrugations on the bellows. The more the wave number, the stronger the compensation, but the fatigue life will decrease. How to balance? My advice is: Do not exceed the wave number required for the design compensation. For example, you need axial compensation of 30mm, check itModel and size of expansion jointTable, choose a wave number that can just satisfy, don't be greedy for more.
Compensation amount: Each expansion joint has a rated compensation amount. You calculate the thermal elongation of the pipe: Δ L = α × L × Δ T (α is the linear expansion coefficient, L is the length of the pipe, and Δ T is the temperature difference). After calculation, select the model whose compensation amount is greater than or equal to 1.2 times the calculated value, leaving some margin. For example,Universal corrugated expansion jointUsually the compensation range is 10~50mm. If it is a large flue, it may be necessary to useLarge diameter thick wall expansion joint。
Don't forget to look at it at the endstiffness(Stiffness and Calculation Formula of Bellows) -The greater the stiffness, the greater the thrust on the pipe frame. If the pipe frame is not strong, choose a multi-wave structure with low stiffness.
Step 4: Do three things before installation-check, position, and remove the screw (don't rush to weld)
When the goods arrive, don't rush to put on the tube. Do three things:
- Check the appearance:Are there any bumps and scratches in the bellows? Is the guide tube in the right direction (the arrow points to the direction of media flow)? How tight is the tie rod nut? Many expansion joints leave the factory for the convenience of transportation, the tie rod is locked and has to be loosened.
- Positioning:Flue-type corrugated expansion joints are usually installed in the middle of pipe segments or near fixed brackets. Pre-install it first, don't solder it to death. Use a jack or hand-pulled hoist to adjust the pipe to the design position so that the expansion joint is in the "zero" state (i.e., unstressed state).
- Remove screw:This is the easiest step to overlook!Does the screw of the expansion joint need to be removed?The answer is: the transport screw must be removed! It is temporarily fixed, and the expansion joint can't be freely expanded and contracted without dismantling it. But if it isExpansion joint tie rod nut(protective tie rod used to limit over-stretching), then retain and adjust after installation. Can you tell the difference? Simple: The transport screw is a slender bolt that runs through the inside of the bellows, and the tie rod is a thick rod on the outside. The former must be dismantled, and the latter must be adjusted according to the instructions.
Tips:After removing the screw, shake the bellows with your hand to make sure it is not stuck. If there is abnormal noise, it means that there are debris inside or the guide tube is crooked, so it has to be dealt with.
Step 5: Don't go in a hurry after installation-test the pressure, check for leaks, and adjust the tie rod nut
Don't leave in a hurry after welding or flange tightening. Do three things:
- Pressure test:Perform a hydraulic test at 1.5 times the design pressure (if it is a flue with high air tightness requirements, use the air pressure test). Hold the pressure for 10 minutes, and observe whether there is any bulge and leakage on the surface of the bellows.
- Check for leaks:Focus on the weld, flange connection and bellows trough position. Brush it with soapy water to see if there are any bubbles.
- Adjust tie rod nut:If the expansion joint has a limit tie rod, loosen the tie rod nut after the pressure test, leaving the compensation gap required by the design. How exactly to adjust?How to adjust the tie rod nut of expansion joint— — Usually screw to just contact first, and then retreat 1~2 pitches as margin. Note: Don't screw too tightly, otherwise the tie rod limits the expansion, which is equal to white installation.
And guess what? I have seen someone finish installing the pressure test without any problem, but the tie rod was not adjusted, and the pipe directly broke the bellows when it was hot. Alas, all the previous efforts were wasted.
Step 6: The routine maintenance thing-how often do you check it? Which places are prone to problems
Installed doesn't mean once and for all.Service life of expansion jointIt is directly related to working conditions and maintenance. Approximate frequency:
- Quarterly:Visually check the bellows surface for corrosion, cracks and fatigue marks. Focus on the peaks and troughs, which are stress concentration zones.
- Once per year:Measure the actual displacement of the expansion joint to see if it exceeds the design value. If you find that the amount of displacement suddenly increases, there may be a problem with the pipe support.
- Special attention should be paid to the flue:Accumulating dust! The dust in the flue gas is easy to accumulate in the bellows trough, which affects the expansion and contraction. It is recommended to clean it regularly, or add it during installationexpansion joint guide tube(This site has a detailed description of its function), which can reduce dust accumulation.
In addition, if the tie rod nut is found to be loose or corroded, replace it in time. Don't delay, small problems can lead to big accidents.
Okay, from selection to installation to maintenance, no step was left behind. According to these six steps, the flue corrugated expansion joint basically won't make a big basket. If you are still unsure, just look through the product information on the site — —Metal hose、rubber compensator、Non-metallic expansion joint…The classification is very detailed, just take the right seat.