Don't be in a hurry to dismantle it: How do you judge if your flue expansion joint should be replaced?
Equipment leakage is the most troublesome place, especially the flue expansion joint-the space is narrow, the temperature is high and the dust is large, so a leak is troublesome. But don't rush to shut down the power as soon as you see smoke. Take two minutes to judge: Is the expansion joint itself broken?
You walk to the scene and listen to whether there is a "hissing" air leak first, which is the most direct. Then use the back of your hand (don't use the palm of your hand, hot!) Near the flange interface to feel it. Is there hot air spewing out? If you find that there are moisture traces (flue gas condensate) on the flange surface or dust accumulates unevenly, it is basically inseparable. In addition, look at the body of the expansion joint: if it is a non-metallic expansion joint, is there any cloth layer tearing and bulging? If it is a metal corrugated expansion joint, are there any obvious cracks or corrosion pits on the bellows surface?
As long as the leak point is not on the weld joint or pipe wall perforation, it's just a seal failure or corrugation damage on the expansion joint itself, you have every chance of replacing it online.That is, it operates under the condition of not stopping production, not turning off the fan, and keeping the system under slight negative pressure. However, the premise is that the working conditions permit-the medium temperature is below 80°C, there are no flammable and explosive gases, and there is room for maintenance at the site. When you encounter a high-temperature and high-pressure steam pipeline, you must stop it.
✅ Air leakage sound + hot air sensed on the back of the hand → flange seal failure
✅ Expansion joint surface bulging, tearing → body damage
✅ Tie rod bolts are obviously loose or falling off → installation preload failure
If you hit any of the above, don't hesitate to change it.
What should I prepare for online replacement? Don't miss these guys
Knowing that you need to change it, but not bringing all the tools, that's called being blind. The core principle of online flue expansion joint replacement is "fast, stable and accurate", and you can't make the production line wait for you for half a day. So before you start work, prepare the following things:
- New expansion joint: Select according to the original model, don't buy it blindly. For example, the original use isNon-metallic expansion joint (fabric fiber expansion joint)The new piece has to be of the same material and size. If it's metal, likeUniversal corrugated expansion jointOrHigh temperature axial expansion jointDon't forget to check the nominal diameter, pressure and compensation amount.
- Sealing gasket or sealant: The flange surface needs to be resealed after cleaning. It is recommended to use high-temperature resistant asbestos gasket or silicone rubber surface sealant. Don't use ordinary rubber gasket cheaply, otherwise it will leak again in half a month.
- Toolkit: Open wrench, plum wrench (corresponding to the tie rod nut size), knock wrench (if the bolt is rusty), wire brush, sandpaper, crowbar, flashlight. By the way, there is also a torque wrench-the rear adjustment lever works.
- Safety equipment: High temperature resistant gloves, goggles, dust masks. There is a lot of dust in the flue, so don't suck it in.
- Auxiliary tool: If the flange bolt rust, prepare a bottle of loosening agent (WD-40 or the like); If space is tight, prepare extended sleeve rods.
Tips:After the new expansion joint is unpacked, check the guide tube orientation (if any) and the arrow marking first. Many novices are planted in this step-install it backwards, and the airflow washes directly on the bellows, which wears out in a few months.
Teach you to change it step by step: dismantle the old, clear the flange and install the new expansion joint in three steps
Step 1: Demolish the old
You first find the tie rod nut on the expansion joint-don't remove the flange bolt as soon as it comes up. The correct order is:First loosen the locking nut on the pull rod, and loosen the pull rod to the free state。 Why? Because the tie rod usually carries pre-compression or pre-tension force, if it is not released, the expansion joint will suddenly bounce open when removing the flange bolt, dangerous!
After loosening the tie rod, remove the flange bolts. Pay attention to diagonal removal, starting with the farthest bolt, leaving the last two without removing it first, and using a crowbar to pry open a little gap to make sure there is no pressure inside (you can try it with a piece of paper to see if the paper will be sucked in). Then remove the old expansion joint completely, being careful not to let it fall and hit someone.
Note:Don't throw out the old parts that have been removed, and keep the comparative size-for fear that the new parts manufacturer will send the wrong goods.
Step 2: Clean the flange
Scrape all the old gaskets, rust residue and oil stains left on the flange surface. Use a wire brush with sandpaper. If the flange surface has deep pits or severe deformation, it must be smoothed with a file. Don't be lazy, this step determines whether the new expansion joint leaks after being installed.
Once cleaned up, wipe it over with a rag dipped in alcohol and let dry.
Step 3: Install new expansion joints
Lift the new expansion joint, pay attentionThe direction of the arrow must coincide with the flow direction of the medium— This question will be detailed in the answer, so do it first. Align the bolt holes and screw all nuts on by hand, then tighten them in diagonal order in 2-3 times. Don't screw to death all at once, take it step by step. Recommended torque value: about 80-100N·m for M16 bolts, 120-150N·m for M20, depending on working conditions.
Once the flange is installed, go back and adjust the tie rod nut. How to tune it? Look at next.
Don't relax after installation: check the seal, adjust the pull rod, and test the leak.
The expansion joints are installed, but the work is not done yet. There are three things that must be done, none of which can be missed.
Check the seal:After the flange bolts are tightened, use a flashlight to shine a circle against the gap to see if there is any light transmission. If so, it means that the bolts are not evenly screwed or the flange surface is uneven. Don't rush to make up the twist at this time. First, loosen it and twist it diagonally again.
Adjust the pull rod:The role of the tie rod is to limit the excessive stretching or compression of the expansion joint, while ensuring the amount of pre-deformation during installation. How to tune it? Look at the design drawings-if there is no drawing, refer to the length of the tie rod of the old piece. Generally speaking, for axial expansion joints, installation requirementsThe amount of pre-compression is equal to half of the thermal elongation of the pipe。 For example, if the pipeline will extend by 20mm after operation, then pre-compress the expansion joint by 10mm. Adjustment method: twist the tie rod nut to shorten the bellows by 10mm and measure with a caliper. If it is a non-metallic expansion joint, it is usually not pre-compressed, and the tie rod is only a positioning function. Just lock the nut to just touch the retaining ring.
Leak test:After the system is back in operation, spray soapy water on the flange joints and the expansion joint body to see if there are any bubbles. You can also use an ultrasonic leak detector, which is more accurate. If there is a leak, stop the machine to re-tighten or replace the gasket. Generally, online replacement allows micro-leakage, but running smoke and gas will pollute the environment, so try to achieve zero leakage.
It's done after changing? Keeping an eye on these points daily can be used for several years
To be honest, many expansion joints are not used bad, but "raised" bad. After replacing new pieces, you can save a lot of money by paying more attention during your daily inspection.
- Take a look at the tie rod nut every week: Is it loose? If it is found that the nut has retreated outward several turns, it means that the pipe displacement exceeds the design value, and the bracket or guide needs to be checked.
- Touch the surface temperature of the expansion joint every month: Local temperature abnormality (for example, a certain area is particularly hot), which may be caused by the detachment of the guide tube or internal scaling. EspeciallyUniversal corrugated expansion jointWhen the temperature of the bellows exceeds the design value by more than 20°C, the life of the bellows is directly halved.
- Pay attention to any abnormal noise in the flue: The sound of clicking, the high probability is that the guide tube fell off and was blown back and forth by the airflow. This has to be shut down or the bellows will be cut.
- Clean up dust near flanges regularly: After dust absorbs water, it will accelerate the corrosion of flange bolts. Check the state of bolts once every six months, and change them when they should.
- Record Replacement Date and Model: Don't rely on your brain to remember, you will definitely forget after half a year. Make a ledger and stock up in advance next time.
Two days ago, a brother from a cement factory told me that the non-metallic expansion joints of their factory have been used for three years without any problems, just because they tighten the bolts every time they inspect. You taste, you taste.
Answer a question: Where does the expansion joint arrow point? How much do tie rod nuts adjust?
Q: Where does the arrow on the expansion joint point?
A: pointed by an arrowIs that flow direction of the medium。 This is not randomly drawn. One end of the arrow is the exit direction of the "deflector tube". If you install it backwards, the airflow can directly scour the bellows (especially the metal corrugated expansion joints), causing premature fatigue cracking. The same is true for non-metallic expansion joints. If the arrow points incorrectly, the cloth layer will be torn by the air flow in the opposite direction. So take a look at the arrow before installation, and review it again after installation.
Q: How much is the tie rod nut adjusted?
A: There is no fixed value for this, which is related to the compensation amount of pipeline design. But there is a general principle:Free length of expansion joint at installation = design length ± amount of pre-deformation。 The amount of pre-deformation may be pre-stretching (when the pipe is cold contracted) or pre-compression (when the pipe is thermally expanded). For the working condition of the flue from normal temperature to about 300°C, in most cases, pre-compression is done, and 50% ~70% of the axial expansion of the pipeline is measured by compression. If you don't calculate the data, the easiest way: after installation, let the tie rod nut just press the spring washer or retaining ring, and then screw in about 1~2mm of pre-tightening. Note that the tie rod is not used to bear the thrust of the pipe, but only to limit the position. Don't screw it too tight. After adjusting, try it with a hand feel. The bellows can move slightly, but it won't shake greatly, which is right.
Well, you can follow this method of replacing flue expansion joint online. As long as the tools are complete and the operation is standardized, you can do it without stopping production. If you are still unsure, you can flip through our siteCorrect installation method of expansion joint of large tie rodAndFunction of expansion joint tie rodThese two articles, there are more details in them.