Selection and installation of flue flue expansion joint: follow these 5 steps to avoid falling pits
Two days ago, a buddy who was doing a desulfurization project spat with me, saying that the fluororubber flue expansion joint I bought cracked in less than three months after it was installed, and I was so angry that I hit my thigh. After asking, he found out that he didn't know the actual temperature in the flue at all, so he bought the general-purpose model by feeling. And the result? The white silver was wasted. This is not uncommon. Today, I will break these five steps apart and crumble them into pieces to tell you. Follow it, and I guarantee that you will waste money.
Step 1: Find out your flue conditions and don't let the fluorine dry
When choosing fluororubber flue expansion joint, the most taboo thing is to guess by experience. You have to take out a little notebook and make three numbers:
- Medium temperature: What exactly is the long-term operating temperature? Is it over 250℃? Note that this is a continuous temperature, not an instantaneous peak. For example, the flue exhaust temperature of power plants is often 150-180℃, but the inlet of some desulfurization towers can soar to 220℃, so ordinary fluororubber (FKM) can't bear it, so perfluoroether rubber (FFKM) has to be considered.
- Corrosive gas composition: What acid is in the flue? What is the concentration of SO₂, HCl, HF…? Don't just look at variety, concentration is the key. For example, with 10% HCl and 1% HCl, the corrosion rate of rubber is more than ten times worse. If you are not sure, it is best to take a gas sample for analysis, or directly ask the manufacturer for a corrosion resistance data sheet.
- Pipeline displacement: How many mm displacements are there in the axial (telescopic) and transverse (vertical) directions? This data usually comes from pipeline stress analysis reports or field measurements. For example, between two fixed brackets, the thermal expansion may reach more than 100mm, so the compensation amount of the expansion joint you choose has to cover this number, and you have to leave a margin.
After remembering these three numbers, choosing the type later is like ordering from the menu, which is very simple.
Step 2: Choose the appropriate formula and structure according to the working conditions
Viton rubber is not a panacea, and the difference between grades is greater than you think. Ordinary fluororubber (FKM) is generally resistant to 250℃, and its acid resistance is okay, but it is still finished when it encounters strong oxidizing acids (such as concentrated sulfuric acid and smoking nitric acid). When encountering the combination of high temperature (> 250℃) + strong acid (such as HF and concentrated HCl), decisivelyPerfluoroether rubber (FFKM)The lining, although the budget has to be doubled up several times, is better than changing it every three months, right?
Structurally, the most common flue expansion joint isNon-metallic expansion joint(i.e. fabric fiber expansion joints) that loop-type structure. The middle fluororubber layer is sandwiched between the multi-layer fabric and the metal mesh, with metal flanges at both ends. The advantages of this structure are large compensation, high temperature resistance and vibration isolation. If you need more axial displacement, look at the stationrubber compensatorProduct page, some models are designed specifically for large displacements. How to match it specifically? To our stationNon-metallic expansion joint (fabric fiber expansion joint)Andrubber compensatorJust search the page and take the right seat.
Step 3: Preparation before installation-inspection, cleaning, centering
Don't screw the bolts as soon as you get up! Let me tell you, the roughest installer I have ever seen. Even the welding slag on the flange surface is not clear, so he directly pushes the expansion joint up. As a result, the rubber is punctured after compression and leaks a mess. Come, in order:
- Clean the flange surface: Use a wire brush or sandpaper to clean all welding slag, rust and burrs on the contact surface between the pipe flange and the expansion joint flange. Note: fluororubber is afraid of sharp objects, flange gasket must be smooth, it is best to use special corrosion-resistant gasket, don't make do with ordinary asbestos pad.
- Check Alignment: Use a level or ruler to check whether the two flange surfaces are parallel. Deviation more than 2mm? Then you'll have to adjust the pipe bracket. How to tune it? Loosen the bolts on the adjacent brackets, add padding iron or raise the supports until parallel. If this step is not done, as soon as the bolt is tightened, the expansion joint will be crooked, and the life will be cut in half directly.
- Confirm Installation Direction: There are arrows on some expansion joints, which is the flow direction of the medium. Don't install it backwards. There are also models with deflectors (e.g.expansion joint guide tubeRelated products), the other end of the guide tube must face the direction of incoming flow, otherwise the airflow will directly scour the rubber layer and accelerate wear.
If the installation environment is dusty, it is best to blow the flange surface with compressed air, and then apply a thin layer of grease (high temperature resistant), which is both rust-proof and easy to dismantle.
Step 4: Installation operation-the tightening sequence of pull rods and bolts is particularly
Hoist the expansion joint in place first and thread the bolts, but don't screw them to death. Then pressDiagonal sequenceGradually tighten 3-4 times, about 1/3 turn each time to ensure even force. This principle is the same as changing a tire. Tightening one corner at a time will cause the flange to deform.
If you use a model with a tie rod (like the one we stand onexpansion joint tie rodRelated Products), Note: After installation, be sure to loosen the tie rod nut1-2mm！ Why? Because the pipe will expand as soon as it is heated, if the tie rod is locked, it is equivalent to forcibly holding the expansion joint, and the structural stress is all transferred to the rubber layer, which will be torn after several heat cycles. Many people have stepped on this pit, and I have seen a power plant project with my own eyes. The tie rod was not loose, but it exploded on the first day of trial operation.
Apply a little anti-bite agent (copper-based or nickel-based) on all threads to make it effortless to disassemble and assemble later. Especially in the high-temperature flue, the bolts are easy to rust to death, and when the expansion joint is changed, it will be sad.
Step 5: Trial Run and Daily Inspection-Don't just leave it alone
After the media is in, don't leave in a hurry. Stand by and observe for half an hour, listen to any abnormal noise (hissing, puff), and see if there is any air leakage (you can apply soapy water to the flange seam, blistering is leakage). After 24 hours of running, tighten the bolts again-because the fluorine hasCompressive creepIt is still elastic when it is first pressed, but it will thin slightly after a while, causing the bolts to loosen. At this time, twist it again, pay attention to the diagonal order, and don't use too much force to crack the rubber.
Is the flange connection loose? Is there any crack, bulge or discoloration on the rubber surface? If there is dust or scale in the flue, it should be cleaned up in time, otherwise the accumulation will accelerate the aging of fluororubber-the acidic dust will gradually penetrate into the rubber layer, just like slowly nibbling on you. Also, don't forget to checkExpansion joint tie rod nutIf it is found that the gap is gone (indicating that the displacement of the pipe has exceeded the design value), you have to adjust the tie rod or recalculate the displacement.
Buy flue flue expansion joint, don't try cheap. The cheaper ones are often recycled fluororubber or mixed with fillers, which are poor in temperature and corrosion resistance. Okay, have you remembered these five steps? Anyway, next time someone asks me "how to choose expansion joints", I will dump this article directly to him.