Let's talk about something real first: what pieces of metal expansion joints are put together?
Don't be fooled by those fancy nouns. The core is these pieces-bellows, end pipes, guide tubes and tie rod bolts. However, behind each combination, there is a completely different working condition logic. For example, it is also a bellows, which is used in the power station industryHigh temperature axial expansion jointAnd cement industryMetal Corrugated Expansion Joints in Cement IndustryThe wall thickness and waveform parameters can be twice as different. The former should cope with the axial thermal displacement of steam pipeline, and the waveform is often designed to be deep and dense; The latter is used for the high-temperature air duct at the tail of the kiln, the medium temperature is always above 500℃, the wall thickness has to be thickened, and the waveform has to consider fatigue resistance. What's the use of just knowing names, you say? Gotta figure out how it fits.
The bellows is the soul, but it's not just a roll of iron
Single or multi-layer? Is the waveform U-shaped or ω-shaped? Choose 304 or Incoloy825 for material? There are a lot of doors here. For example,Universal corrugated expansion jointAustenitic stainless steel is usually used, and the number of layers is calculated according to the compensation amount and pressure-if the compensation amount is large, use more layers, and if the pressure is high, the wall thickness of a single layer will be thickened. But encounter a vacuum environment, such asDouble hinge expansion joint of air-cooled island vacuum pipeThe external pressure instability must be considered. At this time, the waveform design is just the reverse: the U-shape becomes the ω-shape, which increases the ability to resist external pressure. And guess what? In order to save money, some projects change the wall thickness of the ordinary expansion joint. As a result, the vacuum bellows will deflate as soon as it is pumped, and the equipment will be directly scrapped. Tsk, that's the price of not understanding the composition.
End tube and guide tube: Looking inconspicuous, in fact, it is most easily overlooked
The end pipe is responsible for welding to the pipe, and the material must match the main pipe. Different steel welding, such as carbon steel pipes with stainless steel end pipes, a transition layer must be added in the middle, otherwise cracks will appear after several thermal cycles. Two days ago, I met a customer who asked why the expansion joint leaked for half a year. When I disassembled it, I saw that the guide tube was seriously worn and the bellows was directly exposed. It was strange that it was not bad. The function of the guide tube is to protect the bellows from being washed by high-speed media-especially the flue gas or steam pipeline containing particles. As soon as the particle speed goes up, no guide tube is equivalent to grinding the bellows with sandpaper every day.Specific Function of Expansion Joint Guide TubeIt is very clear in our FAQ. Simply put, it is "blocking the knife for the bellows". Don't forget to calculate the medium flow rate when selecting the model. If it exceeds 15m/s, you have to consider thickening the guide tube or even changing the material.
Tie rods and nuts: Don't use them as decorations, if you don't install them correctly, you will die
Many people think that the tie rod nut is a fixture, but in fact, it is an insurance against over-stretching or compression of the bellows. Especially inLarge tie rod expansion jointAndCurved tube pressure balance expansion jointOn, the tie rod is also responsible for withstanding the internal pressure thrust. When adjusting, you have to follow the pre-compression amount given by the manufacturer, and don't screw it randomly. Then the question arises:Do you need to remove the screw of the expansion joint？ After installation, the transport screw must be disassembled, but the working tie rod nut must be kept and adjusted in place, otherwise the system thrust is fully pressed on the fixed bracket, and the bracket will collapse sooner or later. We specifically wrote in our FAQHow to adjust the tie rod nut of expansion jointThe core is to screw it to the pre-compression mark position, and then fix it with a locking nut. Some on-site workers try to save trouble, screw the nut to death, the bellows can't move, the compensation function fails directly, the pipeline stress has nowhere to be released, and finally the weld cracks. Whose fault did you say it was?
Let's talk about special variants: both are metal expansion joints, but their structures are very different
Also a metal expansion joint,Desulfurization flue gas baffle doorThe fitted expansion joint must be resistant to acid corrosion, at this timePTFE-lined hoseIt is typical-lining PTFE in metal bellows, which is resistant to negative pressure and corrosion. Whiledirectly buried expansion jointThe outside is wrapped with insulation layer and waterproof layer, mainly to compensate for the thermal displacement of underground pipelines. The structure is completely different from the ordinary general-purpose type, and the end pipe is also lengthened for easy welding. And to deal with high temperature and high pressureExternal pressure single axial expansion jointThe bellows is arranged on the outside and is pressurized by the outer sleeve, thus solving the problem of internal pressure instability. Have you noticed?Metal expansion joint compositionEach piece in it is "grown" for specific working conditions, not thought up by designers patting their heads.
Finally, to conclude: Type selection is not part selection, but logic selection
Don't just look at the nominal diameter and pressure, you have to put out the medium, temperature, displacement direction and installation space, and check it one by one against the product information of this site. For example, the metal corrugated expansion joint in the cement industry is often used in the high-temperature air duct at the tail of the kiln, and the working temperature is often above 500 ℃. At this time, ordinaryrubber compensatorOrNon-metallic expansion joint (fabric fiber expansion joint)-Although the fabric fiber expands, saves energy and resists high temperatures, but the pressure bearing capacity is limited. Another example is the vacuum pipe, which goes directly toSpecial hose for vacuumOrDouble hinge expansion joint for air-cooled island vacuum pipelineDon't make do with regular expansion joints. Figuring out the composition is figuring out the performance boundary. The next time someone asks you which piece of the expansion joint is most important, you can tell him: Every piece is important, but more important is that you know why they are there.