Let's talk about what this thing is
PTFE flue expansion joint, to put it bluntly, is an expansion joint lined with polytetrafluoroethylene (PTFE). Why do you have to use PTFE? Because of the little things in the smoke-sulfur dioxide, hydrogen chloride, hydrogen fluoride, plus the condensate below the acid dew point, ordinary metal pipes can't hold it for three months and start to perforate. PTFE material is naturally corrosion-resistant, the surface does not adhere, and the dust cannot hang, so it is just right when used in the flue.
In our factory's products, likePTFE-lined hoseAndPTFE compensatorIt is a family, and the structural principle is similar. It relies on PTFE layer to isolate the corrosive medium, and the external metal parts are under pressure. However, the diameter of the flue expansion joint is larger, and the requirement of displacement compensation is higher.
Its most frequent haunts
Desulfurization system of power plant, chimney exhaust pipe of chemical plant, flue of sintering machine of iron and steel plant-the flue gas temperature in these places fluctuates greatly. It runs at full load during the day and shuts down for maintenance at night, and the displacement of one cold and one hot pipe is several centimeters. What's more troublesome is the slurry flue gas after wet desulfurization, whose pH value is as low as about 2, and ordinary stainless steel will chew through it for you.
CooperateDesulfurization flue gas baffle doorOrRound Flap Door (Double Seal)The whole system has good sealing performance, and the PTFE lining is not afraid of acid backflow. Two days ago, a customer in the power station industry asked me, he usedCorrugated expansion joint for power station industryHow about this? I said it depends on what medium is in your tube. If it contains sulfur and acid, even if the corrugated expansion joint uses 316L, the weld is easy to intergranular corrosion, and the PTFE lining is more stable.
Compared with non-metallic expansion joints, what's the difference?
Non-metallic expansion joints (fabric fiber expansion joints)Using materials such as silicone cloth and fluororubber cloth has the advantage that it can compensate the displacement of tens of millimeters at a time, and the temperature resistance can reach above 300℃. What about the disadvantages? It is not resistant to long-term soaking of strong acids and alkalis. The condensate after wet desulfurization will slowly penetrate into the fiber layer, and it will bulge and leak over time.
The PTFE flue expansion joint just makes up for this short board. Chemical stability is there, almost invincible except for molten alkali metals and high-temperature fluorine gas. Even if it is soaked in the desulfurization slurry for a long time, the PTFE layer will not age. However, the price is a bit more expensive, about 2 to 3 times that of non-metals. If you have enough budget, choose PTFE; Budget is tight, working conditions are clean, and non-metals can make do.
Focus on these points when selecting models
First, the temperature range.Ordinary PTFE can carry about 180℃. If the flue gas temperature always sways around 200℃, you have to considerHigh temperature axial expansion jointOr add a cooling section to the pipe. Don't overheat, it will decompose directly after PTFE, and the smell will make you remember.
Second, the pressure rating.The flue is mostly slightly positive or negative pressure, but don't forget vibration and displacement. You can turn it overUniversal corrugated expansion jointThe parameter table, refer to the maximum compensation amount and fatigue life. Under the condition of large vibration, the tie rod structure is more stable than the unconstrained one.
Third, the interface form.Flanged connections are the most conventional, followingManual plug-in insulation doorOrElectric plug-in insulation doorWhen matching, be sure to check the flange standards. Some factories use HG/T 20592, and some use GB/T 9119. If you make a mistake, you can't install it, and you have to cut and weld it on the spot.
Say a few words about installation and operation
First, don't screw the tie rod nut too tight. How to tune it? Refer to the question and answer of "How to adjust the tie rod nut of the expansion joint"-first relax to the installation length, fix the pipe and then pre-tighten to the design value, leaving space for thermal expansion.
Second, the direction of the guide tube is correct. The arrow points to the direction of smoke flow. Dressing opposite is equivalent to washing with PTFE layer. You are lucky to wear it out for three months. The specific principle can be seen in "The Specific Function of Expansion Joint Guide Tube".
Third, check the PTFE layer regularly. Bulging, cracking, brittleness, find one for another. Don't think about replenishing it and continuing to use it. Once the PTFE lining is damaged, the acidic condensate directly penetrates into the metal shell, and the whole flue will suffer.
Finally, I want to say something to dig out my heart
Don't buy off-brand cheap. The PTFE flue expansion joint looks simple in structure, but the gap in lining technology is big. Some factories use recycled PTFE powder, which is not densely molded and foams after a few months. Our ownPTFE compensatorAll are pure material molding and sintering molding with uniform thickness.
If you're not sure which one to choose, you might as well call and talk about the work. Temperature, pressure, media composition, pipeline layout, these items are reported, and we will help you calculate the selection. Only when you get the scene did you find out that it was wrong, and it was a waste of time to return and exchange goods.