Two days ago, a friend who is engaged in a boiler spat with me, saying that the expansion joint he bought leaked after only three months of installation. When he removed it, the bellows were deformed. After asking, I found out that the model was selected wrong, and the direction was reversed when I installed it. Actually, this kind of thing is not uncommon. The flue expansion joint of the air duct looks simple, but the wrong choice or wrong use can lead to air leakage and smoke leakage, and the whole pipeline system has to be reworked. Today, we'll break it open and crush it, saying that you will basically not overturn if you follow these 5 steps.
Step 1: Find out exactly what kind of expansion joint do you need for your air duct flue first – metal or non-metal? Rectangular or circular?
Have you struggled with this too? Actually, it is very simple to judge. Look at the temperature and medium first: if the flue gas temperature exceeds 400℃, or the medium is corrosive and the pressure is relatively high, then basically you have to use a metal expansion joint. For example, the one in our stationUniversal corrugated expansion joint、High temperature axial expansion joint, orMetal rectangular expansion jointAll belong to this category. Conversely, if the temperature is low (below 200℃), large displacement needs to be absorbed, or the duct is a rectangular air duct, thenNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion jointMore appropriate. Also likerubber compensator、Rubber PTFE compensatorIt is generally used in low-pressure and normal-temperature flue gas pipelines, which is cheap and easy to install.
That rectangular or circular? Needless to say-if your pipe is square, buy rectangular expansion joints, and if it is round, buy round expansion joints. Don't try to save trouble by forcing the round one over the square mouth, it will definitely not fit.
Step 2: Before installation, these 4 size data must be measured accurately, one less may not be installed
The worst thing I have ever seen is that I measured the wrong outer diameter of the pipe, and the expansion joint flange I bought didn't match. Are you angry or not? So before you start, take a tape measure and measure these 4 numbers:
- OD (or ID) of pipe— — This is the basis of flange matching, not even a millimeter away.
- wall thickness-Affect the selection of gasket thickness when flange connection.
- Installation length— that is, the distance between the two butting flange surfaces. Don't just measure the length of the pipe. The expansion joint itself has the compression amount. This length determines how long you choose the model.
- Circle diameter and hole number of flange bolt hole distribution-It is directly related to whether you can thread the screw in.
If your pipe is an old system and the flange may have been rusted or deformed, it is best to measure it with a caliper. Don't be lazy to look at the drawings. It's too common for the drawings to be a few millimeters away from the scene.
Step 3: Expansion joint installation practice, remember these 3 "never" and 2 "must"
Start playing, huh? Okay, let me start with three things you must not do:
Never hit hard with a sledgehammer— — Put the expansion joint hard on the pipe. The metal bellows will be waste as soon as it is deformed, and the non-metallic fabric layer will break as soon as it is smashed. If it doesn't fit in, check the size. Don't force it.
Never let the welding splash on the bellows— — Especially for metal expansion joints, the welding slag burns a hole. If it has to be welded nearby, be sure to wrap the bellows with a fireproof cloth.
Don't break the fabric of the non-metallic expansion joint— — Even a small hole, when it runs, smoke will flow out from there.
Be sure to see the arrows on the expansion joints。 The direction of the arrow is the flow direction of the medium. Installation backwards will lead to the failure of the guide tube and accelerate the wear. The other isBe sure to adjust the tie rod nut to the design position。 Many expansion joints are locked when they leave the factory to prevent transportation deformation. Once installed in place, loosen the nut according to the instructions and adjust to the predetermined displacement. How exactly to adjust? Our station hasHow to adjust the tie rod nut of expansion jointThe question and answer, you will understand if you go and read it.
Step 4: Don't run in a hurry after installation, do a leak inspection and tie rod adjustment before it is finished
Hey, a customer finished the installation and finished the work. As a result, he didn't do a leak test. Three months later, he found that the flange connection was leaking. In fact, it is very simple: brush soapy water on the joint surface of the weld and flange, introduce low-pressure gas (or blow it directly with the system fan), and see if any bubbles pop up. If there are bubbles, tighten the bolts, or change the gasket.
Then don't forget to check the tie rod. The tie rod of the expansion joint is not an ornament, its function is to limit the excess displacement of the bellows. You want to adjust the tie rod nut to a position that allows the expansion joint to expand and contract freely according to the design documents. If it is a large tie rod expansion joint, the adjustment method is slightly different-in the reference stationCorrect installation method of expansion joint of large tie rod。 Only after this step is completed can the installation be said to be completed.
Step 5: How to maintain it daily? How often to check? What should I do if there is abnormal noise and deformation?
Dressing it up is not once and for all. And guess what? Many expansion joints have problems between half a year and a year. It is recommended to check every six months, mainly looking at three things:
- Are there cracks or corrosion spots in the bellows(Metal)
- Is there any aging, peeling and brittleness in the non-metallic fabric layer
- Is the tie rod nut loose-If loose, the expansion joint may be over-stretched, and the life of the joint is greatly reduced
Don't panic if you hear a noise, such as a "quack". It may be that the tie rod was not adjusted properly and collided with the pipe; It is also possible that the medium flow rate is too high to impact the guide tube. The former just adjust the nut, while the latter needs to check whether the guide tube falls off (the specific function of the guide tube can be seen in the Q&A in the station). If you find that the expansion joint is obviously deformed, bulging, or the non-metallic layer is damaged, then don't repair it and replace it with a new one directly. After all, the service life of expansion joints is only 3-5 years. If you exceed this period, change it if you need to, so don't save that little money.
Well, you can follow these 5 steps, and you can't go wrong with the selection, installation and maintenance. Remember: The air duct flue expansion joint can last for several years if it is installed correctly, but it will throw you every three days if it is installed incorrectly. If you have any questions, feel free to flip through the product information and FAQ in the station, such asMetal hose size comparison table、Expansion joint model and sizeThese can help you avoid detours.