1. Structural disassembly: one depends on corrugation and the other depends on fiber
Although they are called expansion joints, they are completely different things. The core of the metal expansion joint is stainless steel bellows, which absorbs displacement by the deformation of the corrugation. You take one apart and see-the metal is hard, the ripples are layered, like the bellows of an accordion. Our commonUniversal corrugated expansion joint、High temperature axial expansion joint、Straight pipe pressure balanced expansion joint, all belong to the metal bellows family. And fabric expansion joints (also calledNon-metallic expansion jointOrFabric fiber expansion joint) The main body is fiber composite plus rubber/fluoroplastic, and there is a thermal insulation layer inside. The displacement is compensated by the flexure of the fabric and the compression of the insulating cotton. It feels soft to the touch, a completely different species from metal.
Structure determines performance. Metal parts are hard and can carry high pressure; The fabric is soft and can adapt to large deformations. The first step in model selection is to figure out: Do you need rigid compensation or flexible compensation for your piping system?
2. Temperature and pressure resistance: metal can carry high temperature and high pressure, and fabric is specialized in high temperature and low pressure and large diameter
The upper temperature resistance limit of metal expansion joint is generally about 600℃ (stainless steel), and the pressure can reach tens of MPa. Therefore, metal parts are the first choice for high-temperature steam pipelines and flue gas pipelines in power stations and cement industries. In the case of extremely high temperature, we still haveHigh temperature axial expansion jointCan be customized. What about fabric expansion joints? The upper limit of temperature resistance can reach 1000℃ or even higher, depending on the internal high-temperature resistant fiber felt. However, its pressure resistance is weak, generally not more than 0.1MPa. What about that? It is most suitable for low-pressure, large-diameter flue gas systems, such as desulfurization flue and power plant flue duct. pairedFlue gas baffle door、Double-sealed round flapper door(i.e.Round Flap Door (Double Seal)), that's a perfect match.
And guess what? Two days ago, I met a customer who insisted on using a metal expansion joint to connect the rectangular flue at the outlet of the desulfurization tower. The pressure is less than 0.05MPa and the temperature is only 200℃, but the pipe diameter is 3 meters ×4 meters. Metal parts are not only expensive, but also have a large thrust, which pulls and deforms the bracket. Later replaced withRectangular non-metallic expansion jointInstall it adherently, save space and thrust, and solve all the problems.
3. Displacement compensation ability: the metal pipe is multi-directional coordination, and the fabric is naturally suitable for large displacement
Metal expansion energy saving absorbs axial, transverse and angular displacements. LikeCompound hinge transverse expansion joint、Curved tube pressure balance expansion jointA pull rod system can control the force tightly. But there is a problem with metal parts: the hard top has a large resilience. You have to digest this thrust with a pull rod or pressure balanced structure. What about fabric expansion joints? Its axial compensation amount is not very good, but the lateral and angular directions are great. Because the fabric itself is soft, you let it twist a few degrees and misalign tens of millimeters, which is small. Moreover, the thrust of the fabric on the pipe is minimal, and there is almost no reaction force-which metal bellows really can't do.
Air-cooled island vacuum pipeline, not only axial compensation but also to prevent vacuum deflation, we useDouble hinge expansion joint for air-cooled island vacuum pipeline。 The double hinge structure can absorb displacement and withstand vacuum negative pressure. If it is a large diameter circulating water pipe with large lateral swing, fabric is preferred.
Fourth, anti-corrosion and wear resistance: metal is afraid of chloride ions, fabric is afraid of sharp objects
The material of metal expansion joint is mainly 304 and 316L. When encountering wet chloride ion environment (such as the outlet of desulfurization tower), stainless steel is prone to stress corrosion cracking. That's when you have to choosePTFE-lined hoseOrRubber PTFE compensatorTo isolate corrosive media. Fabric expansion joints are not afraid of acid and alkali, and fibers and fluororubber/PTFE liners are in direct contact with corrosive media, so corrosion protection is not a problem. But it is afraid of wear. The smoke is ashed and particles are washed at a high speed, and the fabric layer is quickly worn through.
How to break? Install a guide tube before the fabric expansion joint (expansion joint guide tubeThe role is here), or cooperate withDouble-sealed single-axis round baffle doorUse to allow the airflow to transition smoothly and reduce direct flushing. In addition,Manual plug-in insulation doorAndElectric plug-in insulation doorIt is also often paired with fabric expansion joints, used in situations where pipes need to be completely cut off.
5. Three-step method of selection decision-making: look at temperature, pressure and displacement direction
Does the working pressure exceed 0.1MPa? If yes, go straight to the metal expansion joint. Don't hesitate, fabric can't carry it. Step 2: The temperature is over 600℃ and the pressure is very low? Fabric expansion joints have advantages. For example, the cement industry, althoughMetal Corrugated Expansion Joints in Cement IndustryIt can also carry temperature, but the cost is high. The fabric is cheaper at the same temperature and absorbs greater lateral displacement. Step 3: Is the pipe displacement a large lateral swing or a pure axial expansion and contraction? Fabric is preferred for transverse large displacement, metal is preferred for axial large displacement.
What about complex multidirectional displacements? Composite hinge type or pressure balanced type made of metal. Such asStraight pipe pressure balanced expansion jointAndCompound straight pipe bypass pressure balanced expansion jointSpecialized in dealing with pipeline thrust problems. Another exampleRotary compensatorFor long distance direct burial of steam pipeline. AndSpecial hose for vacuumTo cope with negative pressure conditions. Each model has its applicable scenarios.
In the end, there is no universal option, only the optimal solution. Understand these 5 differences before choosing, and you can take at least half of the detours.