Two days ago, a customer doing a desulfurization project called and asked if he could replace the large flanged non-metallic compensator with an ordinary non-metallic expansion joint. I asked him what the pressure of the pipeline was and whether the medium contained particulate matter. He said that the pressure was 0.15MPa and there was some dust in the smoke. I told him directly- -normal fabric fiber expansion joints (which is what we call in our stationNon-metallic expansion joint (fabric fiber expansion joint)) Under this working condition, the joint will leak for one year. It's not bullshit, it's measured data.
What exactly did the flanging change?
The large flanged non-metallic compensator, to put it bluntly, means that there is an extra circle of outward flange edge at the port of the non-metallic expansion joint. Don't underestimate this circle of flanging, which turns the traditional bolt-pressed wire seal into a face seal. According to the requirements of sealing performance in JB/T 12235-2015 "Non-metallic Expansion Joints" standard, the flanged structure can reduce the leakage rate by at least 30%. More importantly, the flanging increases the contact area with the pipe flange, disperses the bolt preloading force, and does not tear the fiber layer due to excessive local stress like ordinary non-metallic expansion joints.
Structurally, the large flanged non-metallic compensator is the same as the one listed on our siteNon-metallic expansion joint (fabric fiber expansion joint)as well asRectangular non-metallic expansion jointIt belongs to the same family, but the flanging process makes it open the gap in pressure resistance and temperature resistance.
How do you make the cuffing?
Generally, at the end of the non-metallic compensator, multiple layers of fabric fibers (silicone cloth, fluorine cloth, ceramic fiber, etc.) and a sealing layer (such as polytetrafluoroethylene) are folded outward and formed, and then fixed by hot pressing or vulcanization. The flange width usually reaches 50-100mm, which is twice the width of ordinary flange connection surfaces. Wire mesh or wire ring will also be clamped into the inside of the flange to prevent deformation at high temperatures.
- Sealability: As mentioned earlier, face seals replace wire seals. When you hit the torque wrench on the pipe flange, the flange can be evenly stressed, and there will be no situation of "crushing to death on this side and leaking on the other side".
- Resistance to negative pressure: Ordinary non-metallic expansion joints are prone to internal suction deformation under negative pressure conditions (such as the suction section at the rear of the flue gas baffle door), and the flanged structure can resist negative pressure within-0.05MPa due to its higher stiffness. Cooperate with ourFlue gas baffle doorOrDesulfurization flue gas baffle doorThe tightness of the entire flue is guaranteed.
- Compensation amount: The flanging itself does not directly increase the amount of axial compensation, but it allows the pipe to have greater radial displacement, especially on rectangular pipes, matingRectangular non-metallic expansion jointUsed, can absorb displacement in three directions.
Where do you have to use big flanges?
Truth be told, not all occasions require cuffing. For ordinary civil ventilation ducts, ordinary fabric fiber expansion joints are enough. But in the following scenarios, you have to make a big flange:
Flue gas desulfurization system
The flue gas at the outlet of the desulfurization tower has high humidity and acidic condensate, so the welds or joints of ordinary expansion joints are easily corroded and leaked. The large flanged structure can use fluororubber or PTFE cloth as the flanged outer layer, and the corrosion resistance life can be prolonged by 2-3 times. Refer to our siteDesulfurization flue gas baffle doorAndFlue gas baffle doorThese devices often need to be used in conjunction with large flanging compensators to ensure the tightness of the entire flue.
Hot air ducts for power stations and cement industries
of power stationCorrugated expansion joint for power station industryGenerally used in the main steam pipeline, but in the hot air pipeline of 300℃-600℃ in the smoke duct, the cost of metal expansion joint is too high, and the non-metal one is more cost-effective. Large flanges can withstand higher thermal stress because the fiber layer in the flanged area is continuous transition, there is no cut fiber fracture, and there are few thermal stress concentration points. Last case: The kiln tail pipeline of a cement plant was originally replaced with ordinary non-metallic expansion joints every six months. After replacing it with a large flange, the service life was extended to 18 months.
Air-cooled islands and vacuum pipes
I saw that we hadDouble hinge expansion joint for air-cooled island vacuum pipelineThat's metal. But some low-pressure vacuum pipes can save money by using non-metallic ones. Large flanging performs better than ordinary flanging under vacuum, and the reason is the same-the sealing area is large and it is not easy to leak.
The pits during installation must be clearly stated
The flange bolts of large flanged non-metallic compensators cannot be screwed to death in one go. You have to pre-tighten diagonally, apply force in 2-3 passes, and the final torque is controlled within the range recommended by the manufacturer. I saw a construction team at the site, and the electric wrench was beaten hard, and the flange was directly fractured-the flange was not metal, but fiber and rubber, and if it was pressed too hard, it would delaminate internally.
Also, don't forget the deflector. In our FAQSpecific Function of Expansion Joint Guide TubeIs to protect the corrugation (or non-metallic layer) from the medium scour. Large flanged compensator generally comes with its own guide tube (or optional). Note that the direction of the guide tube must be consistent with the flow direction of the medium when installing. The flanged structure itself can withstand a certain amount of erosion, but if there are particulate matter for a long time, the guide tube is necessary.
Also, how to adjust the tie rod of the big flange compensator? As with normal expansion joints: the transport tie rod must be removed after installation (The screw of the expansion joint needs to be removed), otherwise limit the displacement. However, don't rush to dismantle the support frame (if any) of the flanged part. You have to wait for the pipeline to heat up and stabilize before loosening it. These details are in ourHow to adjust the tie rod nut of expansion jointDetailed instructions in the Q&A.
Four parameters for type selection
- Temperature: There is an upper limit for non-metallic materials, silica gel cloth can withstand 250℃, fluorine adhesive cloth can withstand 350℃, and ceramic fiber cloth can reach 1000℃. The sealing layer for large flanging also has to match.
- pressure: Large flanging is suitable for low pressure systems of 0.1-0.3MPa. Over 0.3MPa, metal compensators are recommended (e.g.Universal corrugated expansion jointOrExternal pressure single axial expansion joint）。
- Medium corrosivity: If there is acid or alkali, flanging material should choose polytetrafluoroethylene or fluororubber, in our stationPTFE compensatorAndRubber PTFE compensatorIt's the same type.
- displacement amount: The compensation amount of large flanging itself is not large (generally ≤50mm in axial direction), but it can be increased by increasing the band length. If it is a large displacement condition, consider the double or hinged type.
In addition, do not blindly estimate the size specifications, direct referenceModel and size of expansion jointAndNational standard for non-metallic expansion jointsInside the table. There is no uniform standard number for large flanged compensator, but there are recommendations for flange connection size in JB/T 12235-2015. It is recommended to ask the manufacturer directly for drawings.