Find out what the flue expansion joint looks like first
When you get a flue expansion joint, what is the first thing you see? High probability is a flange with bolt holes at both ends, and a section of bellows bulges in the middle. The metal feels cold, and the surface is rippled in circles; The non-metallic feels soft, like thick canvas. Sometimes there are a few pull rods sticking out from the side, with nuts, which looks quite bluffing. Don't panic, this thing doesn't have many parts. Let's take it apart one by one.
With so many parts, which is the most critical? In fact, each one is useful, but there are only two most prone to problems: bellows and deflectors. Here's a step-by-step teaching you how to recognize them all.
Corrugated pipe-the "heart" of the expansion joint, how to choose the material?
The bellows is the middle bulge, and all telescopic displacement is deformed by it. But there are two kinds of materials, and you have to be able to look and choose.
Metal bellows: The kind used in power stations and cement industries, which feels cold to the touch and has circles of ripples on the surface. It absorbs displacement by the bending of the corrugation, and it must be used when the temperature exceeds 400 degrees. For example, the ones sold in our stationHigh temperature axial expansion joint、Corrugated expansion joint for power station industryAll of them are stainless steel bellows.
Non-metallic bellowsFabric fiber, feels like thick canvas, soft. If there are corrosive gases at low temperature (such as desulfurization flue), choose it, which is acid and alkali resistant, and is not afraid of condensed water. The corresponding product isNon-metallic expansion joint (fabric fiber expansion joint)。 Tip: Don't get confused. If you take the non-metallic one above 400 degrees, it will burn through directly.
How to judge which one to use on the scene? It's simple: look at the flue temperature. When measured by the thermometer, metal is used when it exceeds 400 degrees, and non-metal is used when it is less than 400 degrees but corrosive. If the temperature is high and corrosive... Tsk, that has to be customized, don't make do with it.
Deflector and flange-these two "partners" don't install backwards
Many people don't know what the deflector is for. Simply put, the guide tube is a short tube embedded in the bellows. Its existence is to let the smoke flow smoothly and avoid the high-speed airflow directly impacting the corrugation. You got it? Without the guide tube, the bellows is directly washed by the smoke, and it will wear out in three months.
How to install the deflector?The direction of the arrow (if any) must point to the direction of the flue gas flow. Two days ago, I met a customer. When installing it, the direction of the guide tube was reversed. As a result, the smoke flowed backwards, directly impacting the root of the bellows, and it was torn in two days. The lesson of blood. If you don't know, go and read the Q&A in our station"Specific Function of Expansion Joint Guide Tube", with illustration inside.
flangeIt is used to connect with the pipe. The bolt holes should be aligned, and the gasket should not be put. The gasket material must match the flue gas-graphite gasket for high temperature, polytetrafluoroethylene gasket for corrosive. Don't try to save trouble and spacer, it's more troublesome if it leaks.
Tie rod and nut-the "safety rope" of the expansion joint, don't screw too tight
Most metal expansion joints are locked when they leave the factory to prevent transportation deformation. The first thing you do when installing is to loosen the nut so that the bellows can expand and contract freely. Then how to adjust it? Here are the detailed steps:
- First, loosen the nut on the tie rod so that the end face of the nut is 5-10mm away from the end face of the tie rod.
- After the pipeline is installed and reset, twist the nut back half way-note that it is not screwed to death, but screwed to just touch the end face and then back half a turn.
- Check: Push and pull the expansion joint by hand, and the bellows should be able to expand and contract freely without stuck feeling.
Don't screw too hard, otherwise it means that no expansion joint is installed-when the pipe expands and contracts thermally, the bellows can't move, and the stress is all held on the pipe wall, and the pipe will burst sooner or later.
We have a question and answer on specific adjustment methods"How to adjust the tie rod nut of the expansion joint"Written very clearly, you'd better take a look before you pretend.
Metal vs Non-Metal – What's the Structural Difference?
The metallic ones are deformed by bellows, and the non-metallic ones are laminated and slid by fabric.
Metal expansion joint(e.g.Metal rectangular expansion joint、Corrugated expansion joint for power station industry) There is a guide tube inside and a pull rod outside. The bellows is stainless steel stamped and molded, like the folds of an accordion. Large displacement and high pressure, suitable for circular high temperature pipeline.
Non-metallic expansion joint(e.g.Rectangular non-metallic expansion joint) There is no metal corrugation, but a multi-layer fiber cloth and rubber composite, which absorbs displacement by interlayer friction. Its biggest advantages are cheap, corrosion-resistant, light to install, and it can be made into rectangular-square flue, desulfurization tower outlet, and non-metallic ones are standard.
Are you struggling with which one to choose? Look at the interface shape: your flue is a square interface, so directly choose a rectangular non-metallic expansion joint; If it is a round high temperature pipe, preference is given to metal ones. If it is square and hot…Tsk, then we have to use metal rectangular expansion joints and custom guide tubes. Remember this formula:Metal for round high temperature, non-metal for square low temperature, and non-metal for corrosion, basically no mistake.
After disassembling, do you think the structure of the flue expansion joint is not so complicated? Next time you get the real thing, follow these steps to recognize the parts, and it is stable.