Stainless steel metal corrugated expansion joint, just by hearing the name, you can tell that it is a little related to ordinary metal expansion joint, but the difference is big. To put it bluntly, bellows is its heart, and the material determines how much wind and waves this heart can carry. Today, let's not make a mistake, just break it apart and explain it thoroughly.
How is it different from ordinary metal expansion joints?
Carbon steel and low alloy steel may be used for common metal expansion joints, butStainless steel metal corrugated expansion jointThe core is corrugated pipe-the material is mostly 304, 316L, 321 or even 254SMO. Why? Because the bellows has to be repeatedly bent and deformed, stainless steel has good plasticity, fatigue resistance and corrosion resistance. Think about it, if the pipeline is desulfurized flue gas or high-temperature steam, ordinary carbon steel will rust through in two or three days, and stainless steel can withstand it.
Structurally, the common axial, transverse, angular, and pressure-balanced types-such asStraight pipe pressure balanced expansion jointOrCurved tube pressure balance expansion joint。 The compensation mechanism is very simple: the bellows, like a spring, absorbs the thermal expansion, contraction or vibration displacement of the pipe by elastic deformation. However, it is noted that different structures absorb different displacement directions. The axial type can only absorb axial expansion and contraction, the transverse type can absorb the displacement perpendicular to the direction of the pipe, and the angular type is used at the bend of the pipe. Wrong choice? Equipment is scrapped early.
You can't just look at the nominal diameter when selecting a type
Two days ago, I met a customer and said, "Give me a DN500 stainless steel expansion joint". I asked him what is the medium temperature? How stressful? What is the displacement amount? He was stunned. This reminds me of a saying: Choosing expansion joints only by looking at the caliber is equivalent to buying shoes only by looking at the shoe size, and then wearing them and squeezing their feet.
TemperatureDetermine the material grade-304 for use within 350℃, 321 or heat-resistant alloy for use over 450℃;pressureAffect the number of bellows layers and wall thickness, such as steam pipe pressure 1.6MPa, ordinaryUniversal corrugated expansion jointMaybe you can't handle it, you have to chooseHigh temperature axial expansion joint；MediumDecide whether lining is required-corrosive media such as desulfurization slurry, must be usedPTFE-lined hoseOrPTFE compensator；displacement amountThen determine the wavenumber and structural form of the bellows. For example, large axial displacement can be consideredCompound straight pipe bypass pressure balanced expansion joint, orRotary compensatorTo reduce the thrust.
Don't bother, throw this data to the manufacturer, and they can match you with the most economical plan. Otherwise, in order to save trouble, choose the same diameter but the pressure level is not enough, and it won't take long to change it.
Power stations, cement, desulfurization... which type should be used in different industries?
The industry is different, and the working conditions are very different. For example:Corrugated expansion joint for power plant industryHigh-temperature alloy bellows must be used when the temperature of the main steam pipe is 600℃ and the pressure is above 10MPa, and the structure is usually usedExternal pressure single axial expansion jointOrDirect buried (fully buried) type expansion jointAvoid excessive internal pressure thrust. And the pipelines in the cement industry, with high temperature and dust, needMetal Corrugated Expansion Joints in Cement Industry, bellows with wear-resistant guide tube to prevent solid particles from washing.
What about the desulfurization system? The flue gas temperature of wet desulfurization is not high (50~80℃), but it contains acidic corrosive medium (SO₂, Cl⁻¹). At this timeDesulfurization flue gas baffle doorCooperateNon-metallic expansion joint (fabric fiber expansion joint)More common. However, if it is dry desulfurization or pressure compensation, stainless steel metal corrugated expansion joints still have advantages, such asDouble-sealed single-axis circular baffle doorPiping connections at the back.
Another example is the air-cooled island. The vacuum pipeline needs to bear negative pressure, so it has to be usedDouble hinge expansion joint for air-cooled island vacuum pipelineThe specially designed sealing structure guarantees no leakage. So don't expect one model to conquer the world, the selection must be the right seat.
Can the tie rod nut be removed during installation? How to set the direction of the deflector?
This is the most bug-prone place on the scene. When many engineering teams saw the tie rod nut on it, they thought they would screw it to death, but as a result, the expansion joint had no room to deform. Remember:Function of expansion joint tie rodIs transport protection and must be loosened or removed after installation. How exactly to adjust? Referring to what we wrote earlierHow to adjust the tie rod nut of expansion joint— — Usually, first loosen the nut to a position approximately equal to the compensation amount, fix it by spot welding, and then remove it after the pipeline is installed. Don't tighten it, otherwise it will be for nothing.
The direction of the deflector is more critical. The guide tube is arranged inside the expansion joint,Specific Function of Expansion Joint Guide TubeIs to guide the flow of the medium and prevent flushing of the bellows. The direction of the arrow must coincide with the direction of the media flow during installation. And guess what? Someone installed it backwards, and as a result, the high-temperature flue gas went straight to the bellows, which cracked in half a year. That's a big price.
In addition, the position of the fixing bracket and the guide bracket should also be arranged according to the drawing. There must be fixed brackets at both ends of the expansion joint to guide the displacement to the bellows, otherwise the pipe will fluctuate at the weak point. If these details are not done, no matter how good the expansion joint is, it will be useless.
Stop confusing corrugated expansion joints with rubber compensators and non-metallic expansion joints
Although these three things are all called compensators, the applicable scenarios are very different.rubber compensator(also calledRubber PTFE compensator) Low pressure resistance, generally within 1.0MPa, not resistant to high temperatures, easy to age above 80℃. Its biggest advantage is good vibration reduction effect, suitable for low stress occasions such as water pump outlet and air conditioning pipeline. But if you use it on a power station steam pipe, then wait to blow up.
Non-metallic expansion joints (fabric fiber expansion joints), such asRectangular non-metallic expansion jointIt can withstand high temperatures (even up to 1000℃), but the pressure resistance is extremely low, so it can generally only be used in low-pressure smoke and air ducts. Therefore, it can often be seen in desulfurization flue and smoke exhaust system. However, it is prone to wear, has a short life and needs to be replaced regularly.
WhileStainless steel metal corrugated expansion jointBetween the two: high pressure resistance (up to tens of MPa), wide temperature resistance range (-200℃ ~800℃), long life (design cycle usually more than 8 years). The disadvantage is that it can't dampen vibration and the cost is relatively high. Therefore, when selecting a model, look at the pressure and temperature first, and then decide which one to use. Remember: There is no all-purpose product, only the most suitable scheme.