Flue expansion joint edging, how to choose and install it? Teach you how to do it step by step

Understand first: What is the edging of flue expansion joint used for?

To be honest, when many people buy expansion joints, their eyes are all fixed on bellows or fabric bands, and they don't take hemming seriously at all. And the result? In less than half a year, the edge rotted first, and the smoke went directly out. The expansion joint was equivalent to wasting half of its life. Then what the hell is this circle of hemming for? Simply put, it is the "bulletproof armor" and "sealing strip" of the expansion joint-not only to block the high-temperature smoke and corrosive media in the pipeline from running out, but also to protect the expansion joint body from being worn and scratched. Especially in the flue system, the dust is large, the temperature is high, and there is much vibration. Once the edging is finished, the non-metallic fabric layer or metal bellows inside will be directly exposed to the harsh environment and will soon die. So don't underestimate that circle of cloth or iron, it is a big deal.

Polish your eyes before buying-How to choose edging materials and structures?

When choosing hemming, you first depend on what kind of expansion joint you use. The two most common in our site:Non-metallic expansion joints (fabric fiber expansion joints)AndMetal rectangular expansion joint, the gameplay of edging is completely different. If you are confused, wait for rework.

Hedging of non-metallic expansion joints

The edging of non-metallic expansion joints is usually a composite structure-the outermost layer is high-temperature resistant silicone or fluororubber cloth, reinforced by stainless steel wire mesh sandwiched in the middle, and the inner layer is draped on the edge of the loop band. Pay attention to a few points when buying:

• Material temperature resistance should be matched: If the normal working condition is below 200℃, it is enough to wrap the edge with silicone cloth; If the smoke temperature exceeds 300℃, fluororubber or PTFE cloth must be applied. Don't worry about the money, it's more expensive to change it once it burns out.
• Don't choose width blindly: The edge width is generally 30~50mm wider than the flange edge of the expansion joint, so that the pressure plate can be pressed firmly during installation. Too narrow is not compact, too wide is easy to warp the edges.
• See if there are embedded bolt holes: The edging of some non-metallic expansion joints is drilled when they leave the factory, and the holes are installed directly on the spot; However, many small factories save trouble and don't play them, so you have to draw your own lines and drill holes-remember, the hole spacing is strictly according to the flange bolt spacing, don't rely on your feeling.

Edge wrapping of metal rectangular expansion joint

Metal rectangular expansion joint (like the one in our stationMetal rectangular expansion joint) The edging is often thin steel plate or stainless steel plate, which is welded or riveted on the crest. Find out the material when choosing it:

• Carbon steel edging + anti-corrosion coating: Cheap, but a little acidic gas in the flue (like wet flue gas after desulfurization) is quickly corroded through. It is recommended for use in dry flue gas environments.
• Stainless steel hemming (304 or 316L): It is more expensive, but it is corrosion-resistant and fatigue-resistant, especially the flue of wet desulfurization system, which must be 316L, otherwise it will rust through in one year.
• Thickness: too thin (4mm) will increase the stiffness of the expansion joint and affect the compensation amount. Generally, 2~3mm is more reliable.

"What should I do if the metal rectangular expansion joint I bought is always open for welding?" When I asked, he bought carbon steel for cheap. The welding electrode was not made of stainless steel, and it collapsed directly after thermal expansion and cold contraction. Tsk, this is a typical example of saving a small amount of money and suffering a big loss.

I've tried some of the most easy places to stumble during installation for you

Say a thousand words and ten thousand, if the edge is not well packed, it is equivalent to buying it for nothing. I'll list the points that are prone to problems below, and compare them one by one when you install them.

Installation steps (take non-metallic expansion joints as an example)

1. Clean the flange surface: Polish all the welding slag, oil and rust on the pipe flange and expansion joint flange. Don't be lazy, touch it with your hand, and there can't be a bump.
2. Straightening expansion joint: Hoist the non-metallic expansion joint in place and pay attention to the direction-the guide tube arrow points to the medium flow direction. If there is no guide tube, also make sure that there are no creases on the inner wall of the loop belt.
3. Pre-installed plates and bolts: Put the edge pressing plate (usually also stainless steel bar) on the edge of the pack, screw the bolts diagonally, don't screw them to death, leave a 2mm gap for easy adjustment.
4. Fasten from the middle to the sides: Use a torque wrench to tighten the bolts step by step in diagonal order. For the torque value, refer to the product description. Generally, 80~100N·m is enough for M16 bolts. Do not screw one point at a time, it will pull the edge off.
5. Check if the edging is smooth: After tightening, use your fingers to touch along the edge of the edge pressing plate in a circle, no warping, wrinkles. If so, loosen the adjacent bolts and readjust.

attention: When installing the metal rectangular expansion joint, the edging is welded-be sure to fix it by spot welding first, measure the diagonal size, confirm that there is no misalignment, and then weld it fully. The welding current is not too large, the thin plate is easy to burn through.

Guide to avoiding pits (lessons from blood and tears)

• Pit 1:The wrong material is used for the edging platen. The platen must be matched with the edging material-stainless steel platen for non-metallic edging, and the carbon steel platen will wear down the edging after corrosion. And guess what? I have seen a construction site, all of which were plated with galvanized carbon steel, which all rotted in less than half a year, and the expansion joint fell and smashed the maintenance channel.
• Pit 2:The bolts are tightened too tight. The non-metal edging is a flexible material, and the bolt force is excessive and it will tear directly. Remember: As long as the pressure plate can press the edge tightly without air leakage, don't screw it to death.
• Pit 3:Ignore the thermal displacement direction. Some pipes have large horizontal displacement, and if the edging is only installed according to the conventional, it may be pulled off. At this time, you need to consult the manufacturer whether to add a limit plate on the outside of the edge.

If the edging is broken or leaky, don't rush to replace the whole expansion joint

Found an air leak in the hemming? Don't panic first, and don't place an order for a new one immediately-many times the edging can be repaired separately, and the cost is less than one-tenth of replacing the expansion joint.

• Small hole in non-metallic edging (diameter : Patch with high temperature resistant sealant. Clean the area around the hole, apply silicone high-temperature sealant (temperature resistance above 300℃), then stick a patch cloth of the same material, and compact for 24 hours. If the patch cloth is not readily available, you can use a fluorine rubber cloth for emergency.
• Large area tearing of non-metallic edging: Need to replace the edging layer. Remove the old edge flange bolt, cut the new edge (the material and width are the same as the original), and compress it again with the platen. Note that the newly wrapped bolt holes should be drilled in advance, and do not drill holes on the spot, which are easy to tear.
• Metal edge partial rust penetration: Cut off the corroded section first and weld it with stainless steel sheet (the same thickness). The overlap length should be at least 30mm, smooth polished after welding, and painted with anti-corrosion paint.

Here, if the edging damage has damaged the expansion joint body (for example, the band of non-metallic expansion joint is worn out, and the trough of metal bellows is cracked), then the whole piece can only be replaced. Don't forcefully fix it, safety is important.

Don't take routine maintenance seriously, being a lazy person can last two or three years longer

It usually takes 10 minutes to take a look at this thing, which can save tens of thousands of replacement fees. Is that the truth?

Maintenance Tips (Lazy Edition)

• Purge dust on the outside of the edge with compressed air quarterly: Dust accumulates in the gap between the pressure plate and the edging, and the corrosion rate doubles after being damp. When blowing, don't spray directly on the edge, blow sideways to avoid damaging the sealant.
• Check for loose bolts: Thermal expansion and contraction of pipes can cause bolts to loosen, especially expansion joints close to heat sources. It is recommended to re-tighten with a torque wrench every six months, in the same order as the diagonal twisting method.
• Observe the discoloration of the surfaces of the envelope: If the non-metallic edging is hard, brittle or cracked, it means that the material is aging. Even if it has not leaked, it is best to replace the edging layer in advance. Don't wait until there is smoke on the site to fix it.

Checklist (print it out and post it on the wall)

• [] Is there any damage, bulging or discoloration in the appearance of the hemming?
• [] Is there any corrosion or deformation in the edging platen?
• [] Is the bolt loose? Are there any missing parts?
• [] Is there any trace of air leakage at the junction between the edge and the flange (can be tested with soapy water or smoking agent)?
• [] Is there any media build-up or corrosion on the inside of the edging (if you can look at it)?

To be honest, you don't need to stare at it every day when you do maintenance. You run the flue every quarter and score it according to the list for half an hour at most. Just this half hour can make your flue expansion joint hemming last for two or three years-is this account worth it for you?

Okay, that's all for today's dry stuff. If you don't know anything, go directly to our stationNon-metallic expansion jointAndMetal rectangular expansion jointProduct pages, parameters and drawings are available. Or leave a message and ask me, and reply when you see it.