Find out what "efficient" means first
Two days ago, I met a customer and asked, "How much is your efficient metal expansion joint?" I asked back: Is your pipe running steam or smoke? Are axial displacements or lateral displacements to be compensated? He was stunned for a long time. This problem is actually particularly typical-many people equate "efficient" with "expensive" or "large caliber".
The premise of efficiency is to define exactly what displacement your plumbing system needs to compensate. Is it axial expansion and contraction caused by thermal expansion and cold contraction? Or the lateral offset caused by device vibration? If it is an overhead pipeline, wind load and seismic displacement should also be considered. The compensation object didn't understand it, and everything later was empty.
Which type of metal expansion joint should be selected for different working conditions?
Every structure has its reason for existence, and if you choose the wrong one, it will be useless no matter how expensive it is.
Universal corrugated expansion joint: Suitable for conventional pipelines, pressure and temperature are not extreme occasions. Its axial compensation ability is good, the price is also real, and it is a "all-around oil" type player. But if you use it to absorb large lateral displacements, wait for the bellows to fatigue ahead of time.
High temperature axial expansion joint: It is used in high-temperature and high-pressure pipelines such as main steam and reheated steam of power stations. Its design considers the interaction of high temperature creep and fatigue, and the material selection and corrugation parameters are checked according to high temperature working conditions. At this temperature, the wall thickness and the number of corrugations of the bellows are simply not enough.
Compound hinge transverse expansion joint: Two bellows are connected by hinges, forcing displacement to be converted into angular displacement, especially suitable for absorbing lateral displacement in L-or Z-shaped pipes. If you have to use a single expansion joint to carry the lateral direction, it will be a matter of time before the bellows will become laterally unstable once the force arm is long.
Straight pipe pressure balanced expansion joint: The blind plate force generated by internal pressure is absorbed by the balancing bellows itself, and is not transmitted to the fixed bracket. On high-pressure large-diameter pipelines, this structure is preferred if you don't want the fixed bracket to become a "bunker". AndCurved tube pressure balance typeAndDouble straight pipe bypass pressure balance type, for different spatial and traffic scenarios.
Key parameters affecting efficiency
The more ripples, the smaller the single wave displacement and the longer the fatigue life, but the stiffness and price will also come up. Increased wall thickness can resist compression, but it will reduce flexibility, so it must be weighed.
Many people ignore the deflector tube. It can protect the inner wall of bellows and reduce wear and flow resistance when the medium flow rate is high. However, the guide tube itself will also occupy the circulation area, and if it is not properly designed, it will increase the pressure loss. When selecting the type, be sure to let the manufacturer calculate according to the medium flow rate and allowable pressure loss.
Not to mention the material. 304L and 316L are conventional, with Inconel 625 or GH3030 used at high temperatures, and corrosive media lined. The material is selected wrong, and the expansion joint is perforated before it reaches the design life. What else is high efficiency?
Common pits in installation and O&M
If you don't pretend correctly, no matter how good the expansion joint is, it will be blind.
How to adjust the tie rod nut? The role of the tie rod is to limit the displacement range, and it is not used to deadpull the pipe counter. Screwing too tightly is equivalent to turning the expansion joint into a rigid pipe section, and the compensation ability is directly returned to zero; It is screwed too loosely, and it can't limit the position. The correct way is to adjust to the specified size according to the design drawings and then lock it. After the pipeline is installed, if it is cold and tight, check whether the pre-deformation is in place.
Pre-deformation this thing, simply put, is to give the expansion joint a reverse displacement during installation, so that it is in the best stress state at the working temperature. If the pipeline installed at low temperature and operated at high temperature is not pre-deformed, the actual compensation amount will be discounted.
The arrangement of the guide bracket is more critical. The spacing of guide brackets near the expansion joint is strictly calculated, and it is not just welding a bracket. The spacing is too large, the pipeline is transversely unstable, and the bellows is twisted; The spacing is too small, limiting the axial displacement, which is equivalent to making the expansion joint "unemployed".
Use data to verify whether the selection is efficient
Determining the model by feeling is a big taboo in model selection. The EJMA standard gives the calculation method of fatigue life of bellows, including the core parameters of cycles, displacement, pressure and temperature. The manufacturer will give you the calculation book, which has a key value-the number of fatigue life times. Below design value? Direct rejection.
The stiffness also depends. The stiffness is too large, the expansion joint cannot be pushed, and the pipeline stress is high; If the stiffness is too small, the internal pressure may cause column instability. There is also pressure loss. Under the same caliber, the difference of flow resistance of expansion joints with different structures can reach 30%. You take the formula to calculate the resistance drop, and then decide whether to add the deflector and how long.
A DN800 flue gas pipe with a flow rate of 15m/sUniversal corrugated expansion jointand withCompound hinge transverse expansion jointDo the same displacement compensation, because the former needs more wave numbers to meet the displacement, the length and flow resistance are greater. At this time, if the space allows, the latter is a truly "efficient" metal expansion joint.
Combined with the product line of this site for matching
Back to our own product system, you can build a complete scheme according to the working conditions.
Conventional thermal pipeline, selectUniversal corrugated expansion joint； The main steam and water supply pipelines in the power station, withCorrugated expansion joint for power station industry； The flue at the head and tail of the kiln in the cement industry has high temperature and large dust,Metal Corrugated Expansion Joints in Cement IndustrySpecially done wear resistance and high temperature resistance treatment.
If you want to compensate for lateral displacement,Compound hinge transverse expansion jointAndDouble hinge expansion joint for air-cooled island vacuum pipelineThere are ready-made schemes. Vacuum pipelines should also pay attention to the stability of external pressure, and cannot be replaced by ordinary models casually.
In the flue gas desulfurization system, it is recommended to use corrosive medium and large-size flueMetal rectangular expansion jointAndDesulfurization flue gas baffle doorUse it in conjunction. The baffle door is responsible for cutting off the smoke, and the expansion joint is responsible for absorbing the heat displacement. Each does its own work and does not drag each other down. AndPTFE-lined hoseAndPTFE compensatorSpecialized in dealing with strong corrosive media.
To put it bluntly, the efficient metal expansion joint is not how expensive a single product is, but that every displacement in the whole pipeline system is caught by the most suitable structure. Explain the working conditions clearly and calculate the parameters clearly, and it is not difficult to select the type.