"Old Zhang, our high-temperature steam pipeline needs to be fitted with expansion joints. The drawing is marked with an axial type, but the supplier recommends another model. Who should I trust?" Actually, he is not the only one, thousands of engineers are choosingMetal expansion joint formIt is easy to get dizzy at times-models with similar names, but the structural differences are very different. The wrong choice can lead to air leakage or pipeline cracking. Today, let's not talk falsely, but break up the five core structures and explain them clearly.
1. Axial expansion joint-"telescopic tube" with straight pipe
The axial type is currently the most common form of metal expansion joint, which specifically absorbs the elongation and shortening of the pipe along the axis. It is compensated by bellows deformation. Typical products like the one on our siteUniversal corrugated expansion joint、High temperature axial expansion joint、External pressure single axial expansion joint。 Under high pressure conditions, the external pressure single type is more stable-the outside of the bellows is pressurized, and the belly will not bulge. Then what scene uses axial type? There is a large temperature difference in the straight pipe section, and there is no place for lateral displacement. For example, the steam pipeline rises from normal temperature to 400℃, with an elongation of nearly 5mm per meter. A 20-meter pipeline is 100mm, and an axial type is done.
2. Transverse expansion joint-the "universal joint" of pipeline beating around the corner
The pipeline is not always straight. When you encounter Z-shaped or L-shaped directions, or the equipment interface is misaligned, you have to rely on the horizontal type at this time. Its core is two sets of bellows mated with tie rods or hinges that specifically absorb displacement perpendicular to the axis of the tube. OurCompound hinge transverse expansion jointBig tie rod expansion joints are all this way. For example: the fan outlet pipe needs to be offset by 50mm, so it is definitely impossible to use two axial hardtops, but the horizontal type can be solved with a gentle swing. Remember one thing: the transverse type itself does not bear the blind plate force generated by the medium pressure, and the pressure thrust is borne by the tie rod or hinge.
3. Angular expansion joint-specialized in treating the torsion of "elbow"
If the pipe can only be angled in a certain plane-such as the flue turning from horizontal to vertical-the angular type comes in handy. It rotates the bellows around a point by single or double hinges, aDouble-sealed single-axis circular baffle doorWith the angular type, it can realize the dual functions of sealing and compensation. We still haveDouble hinge expansion joint for air-cooled island vacuum pipelineSpecially used for angular displacement compensation of condenser evacuation pipeline. Angular type is usually used in pairs, and two combinations can absorb lateral displacement, which is highly flexible.
4. Pressure balanced expansion joint-the "pressure stabilizer" of high-pressure pipeline
For pipelines with high pressure and large diameter, the blind plate generated by ordinary expansion joints has a huge thrust, which can push down the fixed bracket. The design of the pressure balance type is to add a balance cavity between the bellows, and use the pressure of the medium itself to offset the thrust. Typical products includeStraight pipe pressure balanced expansion joint、Curved tube pressure balance expansion jointAndCompound straight pipe bypass pressure balanced expansion joint。 Note when selecting: The pressure balance type can absorb axial displacement, but the structure is complicated and the cost is high. Don't use it on small pipe diameter in order to save money. It is suitable for the main steam pipeline of power plants and high-pressure pipelines of chemical plants, which are sensitive to the thrust of fixed supports.
5. Sleeve type and rotary type-the "hard bone" with large displacement
The first four are elastically deformed by bellows, and the compensation amount is limited. When you encounter super-large displacement-for example, the directly buried section of the heating pipeline of nearly 1,000 meters, with a total extension of more than one meter-you have to change your thinking.Sleeve type pipe expansion jointBy the relative sliding seal of the inner and outer tubes, one can compensate for several hundred millimeters. OurRotary compensatorEven better, it uses the rotating sleeve to absorb displacement, long life and maintenance-free. Under the directly buried heating pipeline, useDirect buried (fully buried) type expansion jointWith sleeve type, it can be directly buried underground without inspection well. Did you say it solved the big problem?
Customization of special industry-"Transformers" in the hands of manufacturers
It is not enough to understand these five core structures, and it is often necessary to "magic change" in actual projects. The power station industry hasCorrugated expansion joint for power station industryWhich can withstand high temperature and high pressure and also has a guide tube; The flue gas of cement industry has a large dust content,Metal Corrugated Expansion Joints in Cement IndustryWear-resistant lining plate is added inside; Used under vacuumSpecial hose for vacuumOr vacuum special bellows to prevent deflation; The medium in the flue gas desulfurization system has strong corrosion,Desulfurization flue gas baffle doorCooperateNon-metallic expansion joint (fabric fiber expansion joint)Is standard. AndMetal rectangular expansion jointSpecifically used for rectangular flues,Manual/electric plug-in insulation doorIt has both the functions of cutting off and compensating.
Actual Selection: Four Steps to Lock the Best Form
Don't worry, I'll teach you a four-step method:
- Step 1: Find out the media parameters。 Temperature, pressure, corrosiveness, presence or absence of particulate matter. For example, if the flue gas carries SO₂ at 300℃, the metal material should be 316L or stainless steel, and the bellows should be added with a guide tube (Specific Function of Expansion Joint Guide TubeIs to protect the bellows from erosion).
- Step 2: Calculate the displacement amount。 How much is the axial elongation? How much is the lateral offset? What is the angular displacement? Use pipeline stress analysis software or hand calculation formula to do it.
- Step 3: Match the displacement direction。 Axial displacement is preferential to axial type; There are both axial and transverse directions, and the double hinge transverse type or large tie rod expansion joint is upper; High pressure and large diameter pressure balance type; Super large displacement upper sleeve or rotary compensator.
- Step 4: Check the constraints。 Is the bracket thrust exceeding the limit? Is the interface size correct? Is there enough space? LikeLarge diameter thick wall expansion jointHeavy weight, extra support after installation.
After walking these four steps, you will have a track in your heart. Go back and talk to the supplier and report the model parameters directly. No one can fool you. Choosing the form of metal expansion joint means, in the final analysis, to understand the pain points of each application scenario and prescribe the right medicine. Next time a friend asks, just dump this article to him and be done.