1. Corrugated pipe: the deformation responsibility of the bottom layer is not only as simple as "wrinkles"
When it comes to metal expansion joint construction, the first one that jumps out is definitely the bellows. Many people think it is just a circle of wrinkles, and it is done if it can be stretched-that's only half true. The bellows is indeed the component of the entire expansion joint responsible for absorbing displacement, but its design is far from as simple as you think.
The wall thickness, wave height, wave pitch, number of layers of bellows, every parameter tells you: this thing has to be calculated. For example, the same nominal diameter, used in steam pipes and used in flue gas pipes, the material of the bellows is different. The former should be resistant to high temperature and pressure, usually 304 or 316L stainless steel, while the latter may also consider corrosion resistance, so it can be super austenitic stainless steel. And guess what?Fatigue life of bellowsIt directly determines how many years the entire expansion energy saving will take. This site'sUniversal corrugated expansion jointMulti-layer bellows are used. The more layers, the stronger the pressure resistance, but the deformation stiffness will also change.
The manufacturing process of bellows is also divided into hydroforming and roll forming. The hydroformed bellows has uniform wall thickness, which is suitable for high-pressure occasions; High roll forming efficiency, low cost, suitable for large diameterLarge diameter thick wall expansion joint。 To put it bluntly, the bellows is the "heart" of the expansion joint, and it is the first thing you look at when selecting the model.
2. End pipe and flange: connection depends on them, sealing also depends on them
No matter how deformable the bellows can be, it has to be connected to the pipe, right? That's the end pipe and the flange work. The end pipe is the straight pipe section welded at both ends of the bellows, and the material is usually consistent with the pipe, which is convenient for on-site welding. The flange is a circle of discs with bolt holes used for bolting to equipment or other pipe sections.
Don't underestimate this link. I remember a customer who bought a batchCorrugated expansion joint for power station industryIt leaked when it was installed. After checking for a long time, it was found that the flange sealing surface was not aligned-the parallelism between the end tube and the flange was out of tolerance. Therefore, the end pipe and flange of the serious manufacturer are turned as a whole, and the length of the end pipe is also reserved for welding allowance according to the national standard. In addition, the selection of sealing gaskets is also particular. Metal-wound gaskets are resistant to high temperatures and PTFE gaskets are resistant to corrosion, but they can't be mixed.
This site'sPTFE-lined hoseInside, the flange is directly lined with PTFE layer, which has better anti-corrosion effect. Look back and lookDirect buried (fully buried) type expansion jointIts end pipe also needs to be coated with anti-corrosion coating, because it is directly buried underground, and waterproof and moisture-proof are just needed.
3. Guide tube: the "armor" that is often neglected, but determines the life of the expansion joint
I met a customer who was doing flue gas desulfurization two days ago and bought it backDesulfurization flue gas baffle doorThe matching expansion joint was worn out after half a year of corrugated pipe. I asked him if he had a deflector installed? He looked dumbfounded. "What is a guide tube?"
The guide tube is the thin cylinder in the inner wall of the bellows. It does not directly participate in the deformation, but it does the most painful work: first, it guides the medium to flow along the direction of the pipeline to avoid the high-speed airflow directly impacting the bellows; The second is to prevent solid particles (such as soot and catalyst powder) from depositing at the trough and abrasing the bellows. a great manyMetal expansion joint structureIn, the deflector even affects life more than the bellows themselves-especially for operating conditions containing particulate media.
The thickness of the guide tube is generally 1/3~1/2 of the wall thickness of the tube, and the material is usually the same as that of the bellows, but wear-resistant alloy will be used in some occasions. During installation, the guide tube must be coaxial with the pipeline, and there should be gaps on both sides, so as not to hinder the expansion and contraction of the bellows. This site'sHigh temperature axial expansion jointIn, the guide tube is made particularly thick, because the pulverized coal pipeline is too severely abraded.
4. Tie rod, ring plate and bolt: make the displacement controllable, do not move blindly or get stuck
The bellows can deform, but if you let it twist and twist, it won't take long to crack. So there have to be tie rods, ring plates and bolts to hold it.
Limit the displacement of the bellows to the design range. Such asUniversal corrugated expansion jointThe pull rod is fixed on the ring plate at both ends, and the compression or stretching amount of the bellows is controlled by adjusting the position of the nut. When installing, how to adjust the tie rod nut?How to adjust the tie rod nut of expansion jointThere are detailed instructions in this question and answer-generally speaking, to install the tie rod, loosen the nut first, wait for the pipeline system to be in place, then adjust it to the specified pre-tension or pre-compression amount, and finally lock it.
What about the ring plate? It is welded together with the end tube, and both ends of the tie rod are fixed to the ring plate. The bolt is responsible for connecting the ring plate and the tie rod. This structure looks simple, but it is also quite sophisticated. Such asCompound hinge transverse expansion jointA hinge plate is used instead of a tie rod, which allows lateral displacement but not axial displacement; WhileStraight pipe pressure balanced expansion jointTwo sets of bellows and tie rods are matched to balance the blind plate force generated by internal pressure. Did you see the way? The way each part is combined, determines what kind of displacement the expansion energy saver absorbs-axial, transverse or angular.
5. Differences in the composition of different types of expansion joints-from general-purpose type to pressure-balanced type, the parts combination is completely different
The composition of metal expansion joints is not static. You take oneUniversal corrugated expansion jointAnd aCurved tube pressure balance expansion jointPut together, the number of parts is several times different.
Corrugated pipe + end pipe (or flange) at both ends + guide tube (optional) + tie rod structure. It is suitable for the occasions where the pipe diameter is not large, the pressure is not high, and only absorbs axial displacement.
The pressure balance type is complicated. It has two sets of bellows inside – working bellows and balancing bellows, plus a communicating or bypass pipe. When the medium in the pipeline has pressure, the blind plate forces generated by the two groups of bellows cancel each other, so the pressure balanced expansion joint does not need the main fixing bracket. This site'sStraight pipe pressure balanced expansion jointAndCompound straight pipe bypass pressure balanced expansion jointThe latter can also absorb lateral displacement at the same time.
There are also specially aimed at large displacement conditionsDouble hinge expansion joint for air-cooled island vacuum pipelineIt uses two hinge groups to achieve multi-directional compensation, and there is no tie rod at all in the structure. WhileSleeve type pipe expansion jointThere is not even a bellows inside, and it is compensated by the sliding of the inner and outer sleeves. This is already another technical route.
Therefore, when selecting a model, don't just look at the three words "expansion joint", but disassemble it to see the parts combination inside — —Metal expansion joint structureDetermines what it can do.
6. Only by understanding the composition can we avoid the selection and rollover: inferring the working condition requirements from the structure
Finally, something grounded. Many times customers call and say, "I want an expansion joint of DN500". I asked him what is the temperature of the pipe medium? How much pressure? Is there any vibration? What is the displacement amount? He couldn't answer. We generally dare not accept this kind of list, because if we use the wrong combination of parts, the consequences will be leakage, fracture, and even pipe pull-off.
Conversely, if you understand the composition of metal expansion joints, you can infer backwards:
- When the medium temperature is> 400℃, the bellows must be heat-resistant alloy, the guide tube should be thickened, and the rubber compensator cannot be selected;
- The medium contains particles, the guide tube is standard, and it is recommended to choose the type with wear-resistant lining;
- The pipeline needs to absorb lateral displacement, so don't buy a general-purpose type, chooseCompound hinge transverse expansion jointOrLarge tie rod expansion joint；
- The steam pipe main retainer cannot withstand huge thrust? Use directlyStraight pipe pressure balanced expansion jointSave the cost of civil construction.
In the product list of this site, each expansion joint is marked with applicable working conditions. Such asHigh temperature axial expansion jointIt is clearly written that it is used for the smoke air duct of the power plant boiler,Metal Corrugated Expansion Joints in Cement IndustryIt emphasizes the wear-resistant design. Compare the parameters of your own pipeline, and it is actually not so mysterious to choose a model.
So, stop thinking that a metal expansion joint is a wrinkled iron tube. Bellows, deflectors, tie rods, ring plates, flanges, end tubes-every part is doing business, and none can be missing.