What is a double layer metal corrugated expansion joint? What is the essential difference between it and single-layer corrugated expansion joint?
"Do you have double corrugated expansion joints?”
In fact, this "double layer" does not mean that there is a protective sleeve on the outside, but that the bellows itself is laminated and formed by two layers of metal sheets. The two layers can fit tightly, or a little gap can be left-how to choose depends on the working conditions.
Compared with single layer, the most straightforward advantage of double layer is higher pressure bearing capacity and greater safety redundancy. If the single layer is broken, it will leak. If the double layer is broken, the outer layer will be broken and the inner layer will be able to hold for a while, leaving you a maintenance time window.
Usually seen in our stationUniversal corrugated expansion joint、High temperature axial expansion jointBoth can be made into a double-layer structure. But note: not all occasions are suitable for double-layer change, I will make it clear later.
What pain points does the double-layer design solve?
First, the fatigue of high-pressure pipelines. Each layer of corrugated pipe shares the stress, and the fatigue life can be prolonged by 2-3 times. If you think about it, it is also under pressure displacement. Double layer is equivalent to dividing one person's work between two people, and neither one will be easily tired.
Second, corrosion or erosion of the medium. In case the outer layer is corroded, the inner layer can still hold it, which gives you a window to shut down for maintenance. Especially the sour and hot working condition behind the smoke baffle door. If the single layer is broken, it will be an unplanned shutdown, and the loss will be frightening.
Third, the guide tube cooperates. You know the function of the expansion joint guide, right?guide tubeIs to reduce the direct scouring of the bellows by the medium. The double-layer bellows has greater rigidity and closer cooperation with the guide tube, so it is not easy to generate vortex.
The double-layer metal corrugated expansion joint used in the flue of rotary kiln in a cement plant has not leaked once in three years. Before, it used a single layer, which had to be changed in an average of one and a half years. You calculate, one shutdown to replace the expansion joint with the loss of shutdown is enough to buy several double-layers.
Which industries and working conditions need it most?
Steam pipelines in power station industry, corrosive flue gas pipelines behind desulfurization flue gas baffle doors, and high-temperature air ducts in cement industry-these places have high temperature, high pressure, and the medium may be corrosive, so double layer is just needed.
AndDouble hinge expansion joint for air-cooled island vacuum pipeline、Compound hinge transverse expansion jointIn this kind of situation where complex displacement needs to be withstood, the risk of single layer rupture is high, and double layer can have an additional insurance.
But then again, there is really no need to double-layer rubber compensator conditions at low pressure and normal temperature, such as water systems or ventilation ducts. That thin layer of rubber is enough, and spending twice as much is a waste.
What should I pay attention to when choosing a model? Don't just stare at the word "double deck."
Nominal pressure, design temperature, axial displacement, transverse displacement. Then determine whether you need a guide tube and whether you want to install a tie rod.
Speaking of pull rods,Correct installation method of expansion joint of large tie rodIt has been said in: The tie rod can only withstand pressure thrust and cannot be used to adjust the installation deviation. At this point, many on-site masters will be confused. When installing, they hard screw the tie rod to align the pipeline, and as a result, the bellows will be broken.
Because the stiffness of double-layer bellows is greater than that of single-layer bellows, the reaction force on the fixed support will also increase correspondingly. Many design institutes tend to ignore this detail. The support is not strong enough, and the pipeline is crooked when pushed.
Whether the double-layer tube layers are bonded or not directly affects the compensation amount. The tightly fitted bellows has poor flexibility and high pressure; The double layer with clearance is the opposite-good flexibility but slightly less pressure-bearing. You have to weigh it according to the working conditions.
Why is it rare for manufacturers to actively recommend double layers?
One word – expensive. The double layer uses many materials, the forming process is complicated, and the cost is 30%-50% higher than that of the single layer. Of course, manufacturers are more willing to push products with high profits? No, in fact, many customers shake their heads when they hear the price.
Once a single layer breaks and causes unplanned downtime, the damage can be dozens of times the price of the equipment. EspeciallyDesulfurization flue gas baffle doorIn this kind of frequent start-and-stop working condition, the temperature impact is great, and the double layer is the life-saving talisman. And guess what? After some power plants have been pitted once, they will have to double-layer their names, and even take the initiative to add money.
Some manufacturers simply put two single-layer tubes together to pretend to be double-layered. That thing will rub and generate heat between layers, but it will accelerate its failure, and its lifespan is not as good as a thick single layer. Really qualified double layer metal corrugated expansion joint, two layers are synchronously hydroformed or laminated by special process. Be sure to ask about the craftsmanship details when buying.
The conclusion is a sentence
For high-pressure, high-temperature and high-risk medium pipelines, the upper double-layer metal corrugated expansion joint is a worry-free choice; Low pressure room temperature pipeline, don't waste money.
For specific selection, you can compare the product list in our siteCorrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement IndustryEtc varieties and see which support custom double layers.