1. Who has the final say on the "standard length" of DN500 metal expansion joint? — — Understand these key parameters first
Many people ask "What is the standard length of DN500 metal expansion joint" as soon as they come up. It seems that there is a number that is unified nationwide and written in the national standard. Frankly speaking, the problem itself is a bit off. Because the metal expansion joint belongs to a customized product, its length is calculated by the working conditions, not by slapping the head. You check the national standard GB/T 12777-2019 "General Technical Conditions for Expansion Joints of Metal Bellows", which only stipulates the requirements for design calculation and manufacturing acceptance, and doesn't write how long DN500 should be.
Design compensation amount、wavenumber、Pressure rating、Connection mode, and structural forms. For example, the same DN500Universal corrugated expansion jointIf only used to absorb axial displacement, the length may be short; If it is madeCompound hinge transverse expansion jointTo absorb the lateral displacement, the length is immediately doubled. So, don't be superstitious about "standard length" and figure out what you want it for first.
Second, it is also DN500. Why can the length of the expansion joint be so different? — — The material, wave number and pressure level are all affected
Two days ago, I met a customer and said, "I'll buy a DN500 metal expansion joint, and you can quote me the shortest one". I knew something was going to happen when I heard it. Let's put it this way, under the same nominal diameter, the length difference mainly comes from three aspects:
First, wave number.The displacement absorbed by each wave of bellows is limited, for example, the axial compensation amount of single wave is about 10-15mm. If you need to compensate 50mm, you have to do 4 or 5 waves. The more waves, the longer the length. Note that more wavenumbers are not better, and more wavenumbers are easy to destabilize, so someCorrugated expansion joint for power station industryMulti-layer bellows will be used to improve the pressure bearing capacity, and the length will be increased accordingly.
Second, the pressure rating.The 0.25MPa expansion joint and the 2.5MPa expansion joint have different wall thickness, reinforcing ring and end connection. Under high pressure conditions, it is often necessary to thicken the bellows or useExternal pressure single axial expansion jointThis structure itself is much longer than the general-purpose type. In addition, high-pressure applications are often equippedStraight pipe pressure balanced expansion jointThat was nearly 1.5 meters in length.
Third, the material and operating temperature.Ordinary carbon steel bellows can still be used at 300℃, but they have to be used at 600℃High temperature axial expansion jointInside, thermal insulation layer and guide tube should be added, and these accessories directly extend the overall length. AndPTFE-lined hoseWhen used in corrosive media, liner thickness also affects the overall length.
So don't take a DN500 as the standard answer. The same diameter and length from three to four hundred meters to one meter two are normal.
Third, from general-purpose to power station-specific, what is the typical length range of DN500 expansion joint?
Although there is no absolute standard, according to our years of experience, there is a general range of common models:
- Universal corrugated expansion joint(Axial type): DN500, single-wave form length about 200-300mm, multi-wave (3-4 waves) length 500-700mm. This is the most common one and is used for general duct thermal compensation.
- Corrugated expansion joint for power station industryFor example, the pressure is usually 1.0-2.5MPa, the wavenumber is large and the guide tube is equipped, and the length is usually 800-1200mm. LikeDouble hinge expansion joint for air-cooled island vacuum pipelineBecause to absorb large angular displacements, the length even exceeds 1.5 meters.
- Metal Corrugated Expansion Joints in Cement Industry: In dust environment, wear resistance and temperature resistance are required. A sheath is often installed outside the bellows, and the length will be too long, about 600-900mm.
- High temperature axial expansion joint: There is a thermal insulation layer and thermal insulation filler inside, the typical length of DN500 is 1000-1400mm.
- Rectangular expansion joint: What is said here isMetal rectangular expansion joint, although also a pipe interface for the DN500, the construction is square and the length depends on the layout of the non-metallic compensator or metal corrugation and is usually not comparable.
You can take this range as a reference, but the final length must be calculated and confirmed by the design institute or manufacturer according to the actual displacement, pressure and temperature.
4. When ordering DN500 metal expansion joint, you have to keep an eye on these three data in addition to the length
Length is the result not the cause. When you ask the supplier for a price, just say "I want a DN500 expansion joint with a length of 800mm", and people will probably ask you three data:
1. Displacement amount and direction.Axial, lateral or angular displacement? What is the specific value? For example, the structures selected for 50mm axial displacement and 20mm lateral displacement are completely different-lateral displacement usually requiresCompound hinge transverse expansion jointOr withCurved tube pressure balance expansion joint。 You only quote the length, and the manufacturer can't match the wave number.
2. Pressure level and test pressure.Is the pipeline design pressure 1.6MPa or 2.5MPa? Sometimes customers say "low pressure", but as a result, the pressure impact on the site is great, and the bellows bulges directly. In addition, don't forget to tell the manufacturer if you need to do an airtight test, which affects the end structure.
3. Medium and temperature.Is it steam? Does it contain corrosive gases? What's the temperature? These directly determine the material selection: steam pipes can be used withUniversal corrugated expansion jointAdding a guide tube; Sulfur-containing flue gas must be made of stainless steel or weather-resistant steel; High temperature (> 500℃) must be usedHigh temperature axial expansion jointOrNon-metallic expansion joint。 The more complete the data you give, the more reliable the picture produced by the manufacturer, and the length will naturally come to the bottom.
By the way, some people only recognize the length when they buy expansion joints, and they blame the manufacturer if they can't install them when they take them back. In fact, as long as you give all the parameters, professional manufacturers (such as us) can recommend the most suitable length for you, so you don't need to guess it yourself.
V. Common length misunderstandings at the installation site: what should I do if I can't install it if I am long, and the compensation is not enough if I am short?
Finally, let's talk about two real rollover cases.
Case 1: It's too long to fit.A master in a chemical factory measured the length of the old expansion joint and bought a general-purpose DN500 with a length of 800mm. As a result, the flange spacing of the new pipeline is only 750mm, and the difference is 5 cm. A check found that the old expansion joint wasSleeve type pipe expansion jointWhile the newly bought one is the axial corrugated type, the length of different structures is naturally different. Solution: Either change the connecting pipe section or change to non-standard customization. Of course, if you tell the manufacturer the flange spacing and pipeline direction in advance, this kind of thing can be completely avoided.
Case 2: Short compensation is not enough.In order to save money, a thermal company bought the shortest DN500 expansion joint (single wave 200mm). As a result, when it was hot in summer, the expansion of the pipe reached 40mm, the bellows was directly crushed to death, and the weld cracked. Later replaced withDirect buried (fully buried) type expansion joint, the wave number was increased to 4 waves, the length was 700mm, and there was no problem again. Remember: the smaller the length, the better, the ability to compensate is the hard indicator.
Then what if you buy it back and find that the length is not right? First of all, metal expansion joints are not recommended for on-site cutting and welding, which will destroy internal stresses. The correct way is: if the compensation amount is not enough, you can install a tie rod or replace a model with a larger compensation amount; If there is a deviation in the installation length, you can adjust the pipe support and hanger or add short joints. However, it is best to have the manufacturer provide the installation size drawing and cold tight pre-stretch requirements before ordering. Such asLarge tie rod expansion jointThe tie rod nut needs to be pre-adjusted during installation, and this size directly participates in the total length calculation.
Standard length of dn500 metal expansion jointThe statement itself is not rigorous. Next time you hear someone report "standard length", you might as well ask: "What is your working condition? How much is the compensation? How high is the pressure?" The one who can answer is a reliable supplier.