Two days ago, a customer from a cement factory came to me, and his tone was quite urgent-the metal corrugated expansion joint originally used in their flue leaked in less than half a year, welded and repaired, and finally it was scrapped. He asked me if I had any other way. I said you should try the non-metallic ventilation compensator expansion joint. He was dumbfounded at that time: Isn't that thing soft? Can withstand the heat?
It can be carried, and it is more suitable than metal in many working conditions. I showed him the products on our site- -Non-metallic expansion joint (fabric fiber expansion joint)、rubber compensator、Rubber PTFE compensator-These all belong to what I call "non-metallic ventilation compensator expansion joints". And guess what? After he went back and changed it, it has been two years now, and there is no problem at all.
What's so good about this thing? Let's talk about it today.
1. What is the difference between non-metals and metals?
Metal expansion joints rely on bellows deformation to absorb displacement, which is its business. However, when encountering ventilation ducts with large diameter and large displacement, metal is a little out of power-stress concentration and fatigue cracking are common phenomena. If you think about it, the flue of a cement plant can expand and contract by several hundred millimeters at every turn, and the metal bellows can be carried hard. It's just like letting a weightlifter go to ballet. It's not impossible, but it's easy to get injured.
Non-metallic ventilation compensator expansion joints are completely different. It relies on the elasticity of fabric fiber or rubber itself. To put it bluntly, it means "overcoming rigidity with softness". It is not afraid of large displacements, the installation space can be small, and it is particularly resistant to corrosion. Especially the flue after desulfurization of the power plant-contains acid and humidity, and the metal parts will corrode and wear out in two or three months, while the non-metal parts will carry them for three or five years without any problem. This is why many desulfurization systems, dust removal systems and smoke ducts are now turning to non-metallic compensators.
The pressure capacity is not as good as that of metal. So don't use it for high-pressure steam piping-that'sHigh temperature axial expansion jointOrUniversal corrugated expansion jointJobs. The battlefield of non-metals is an environment of low pressure, large displacement, and corrosive media.
Second, how high is the temperature it can carry?
This question is asked the most by customers. In fact, the temperature resistance range of non-metallic compensators depends on the material formula. Ordinary silica gel cloth with glass fiber layer, the continuous working temperature can reach 250℃. If polytetrafluoroethylene or special ceramic fiber is used, it is not impossible to instantly resist the temperature to 1000℃. On our stationNon-metallic expansion joint (fabric fiber expansion joint)Multi-layer composite structure is usually adopted: the outermost layer is rubber or fluororubber with good weather resistance, the middle is a reinforcing layer, and the inner layer is fluoroplastic or Teflon with temperature and corrosion resistance.
What non-metallic compensators fear most is not high temperature, but open flame. If you have unburned sparks coming out of the flue, no good fabric can carry it. At this time, it is necessary to work withFlue gas baffle doorOrDesulfurization flue gas baffle doorUse it together-isolate first and then compensate, which is the complete scheme.
Third, why are cement plants and power plants rushing to change?
A DN2000 metal corrugated expansion joint costs 20,000 to 30,000 yuan, so you have to find lifting equipment for installation, and it should be replaced at least once in five years. The price of the non-metallic ventilation compensator expansion joint of the same specification is only 1/3 of that of metal, and its weight is so light that two people can lift it. When installing, the flange is butted and the bolts are tightened. Moreover, the elastic modulus of the non-metal is low, the thrust on the pipe support is minimal, and no additional reinforcement is needed.
Another, the non-metallic compensator can also reduce noise and vibration isolation. The airflow noise and fan vibration in the smoke duct can be reduced by 5~10 decibels after being absorbed by the non-metallic layer. Many engineers didn't expect this added value at first, but they all said it was fragrant after using it.
Will it age? Yes. Both rubber and fabric have a lifespan, but the construction of the non-metallic compensator makes it easy to inspect online-the outer rubber cracked only affects the appearance? No, there are also reinforcing layers and sealing layers in the inner layer. The actual failure mode is usually gradual, not sudden cracking of metal. Moreover, you don't have to stop the whole system when replacing it, just remove the flange. If the bellows of the metal expansion joint is cracked, it often needs to be cut and welded as a whole, which is more troublesome.
4. What pits should be avoided when selecting?
First, don't be fooled by the "temperature resistance" parameter. The temperature resistance written by some suppliers is 300℃, which is actually a short-term limit temperature, and the long-term working temperature may only be 150℃. When we select the model, we must confirm the continuous working temperature and leave 20% margin.
Second, non-metallic compensators can be divided into rectangular and circular shapes. Rectangular ones are used for square flues, such as the ones on our stationRectangular non-metallic expansion joint； Round for round pipes. The wrong shape won't fit.
Third, are there many solid particles in the medium? If the dust is large and the flow rate is high, it is best to add wear-resistant lining to the inner wall, or chooseRubber PTFE compensator— — PTFE layer is wear-resistant and anti-stick.
Fourth, don't forget the matching flapper door. If the pipeline needs to be isolated for maintenance, it can be cooperatedElectric plug-in insulation doorOrManual plug-in insulation doorUse. Especially for the desulfurization system, it is necessary to use double seal structureDouble-sealed single-axis circular baffle doorOtherwise, leaking a little acid gas will corrode the compensator.
Five, FAQs and answers
Q: Is there a national standard for non-metallic expansion joints?
Yes, JB/T 12235-2015, which specifies technical requirements and test methods.
Q: Is this thing the same as a ripple compensator?
The function is the same, but the principle is different. Expansion joints and compensators are different names for the same thing. But nonmetallic and metallic are two technical routes.
Q: Do the screws need to be removed during installation?
Non-metallic compensators are generally equipped with transportation rods when they leave the factory, which must be removed after being installed in place, otherwise it will not be able to expand and contract freely.
Q: What is the approximate lifespan?
There is no problem for 3~5 years under normal working conditions. I have seen ones that have not been changed in the desulfurization flue for 8 years-of course, that factory is diligent and does coating maintenance once a year.
At this point, you should understand-the non-metallic ventilation compensator expansion joint is not a substitute for soft collapse, but a preferred solution for low pressure, large displacement, and corrosive conditions. Next time you have a leak in the smoke duct, don't just think about welding metal. Try flexible joints, which may save you a lot of headache money.