Don't rush to count the layers-the layers of the skin are not determined by patting the head
"How many layers is your flue expansion joint skin? I want four layers, strong!" Alas, this matter really can't be done like this. More layers ≠ durability, fewer layers ≠ saving money. Before the three parameters of temperature, medium and pressure are clear, 80% of the layers set by patting your head will flip over. This article does not talk nonsense, directly takes you step by step, and you can match your own skin after reading it.
Step 1: Measure the flue temperature-temperature is the first hurdle
Take out your infrared thermometer or flip through the process drawings and first look at the actual operating temperature in the flue. Don't just look at the design temperature. It is normal for the actual temperature in many sites to be thirty or fifty degrees higher than the design.
- ≤200℃: This temperature range is the most conventional. Generally, 3 layers are enough-the innermost layer of silicone cloth (temperature resistant and sealing), the middle fiberglass cloth (enhancing tension), and the outer layer of fluorine tape (oil resistant and corrosion resistant). Like the flue at the tail of the boiler and the low-temperature flue gas pipe, the three layers are stable.
- 200~400℃: The temperature is up, and the 3rd floor can't hold it. It has to be added to 4~5 layers. How to add? Plug a layer of PTFE film or ceramic fiber blanket in the middle. For example, 4-layer combination: silicone cloth + glass fiber + ceramic fiber + fluorine tape. If you are usingNon-metallic expansion joint (fabric fiber expansion joint)Manufacturers usually embed multiple layers of insulation cotton in the skin layer.
- Over 600°C: Ordinary skin burned directly. At this time, we have to use high-temperature resistant non-metallic expansion joints, like the one in our stationFabric fiber expansion joint, with multi-layer high-temperature resistant insulation cotton (ceramic fiber blanket, aluminum silicate cotton). Under this working condition, the number of skin layers can be 6~8, but the key point is not the number of layers, but that each layer of material can withstand 600℃ +.
Tips: Don't just focus on temperature peaks, look at long-term operating temperatures. Some flue temperature fluctuates greatly, and the highest temperature lasts only a few seconds, which can be relaxed appropriately.
Step 2: Look at media and pressure-the culprits of corrosion and bulging
Temperature fixed? Don't hurry. Is there sulfur in the flue gas? Is there any acid? Is the pipeline positive or negative?
- Corrosive medium (sulfur, acid, chloride): The outermost layer must be made of corrosion-resistant fluoroadhesive tape or PTFE. Like desulfurization flue, the flue gas is full of acidic condensate, and ordinary silicone cloth will rot in a few months. You can choose at this timePTFE compensatorThat kind of skin, or directly let the manufacturer stick a layer of PTFE film on the outermost layer of the skin. By the way,Desulfurization flue gas baffle doorThe matching non-metallic expansion joints and skin are basically high-grade corrosion-resistant.
- High pressure (positive pressure> 10kPa): No stainless steel wire mesh in the middle layer? Just wait for the bulge. If the positive pressure exceeds 10kPa, the skin will be blown into a balloon, which will tear from the flange edge over time. It must be reinforced by a layer of stainless steel wire mesh sandwiched in the glass fiber or ceramic fiber layer. Look at thoseRectangular non-metallic expansion jointUsed in the outlet of power plant fans, there are nets in the middle.
- Vacuum or negative pressure: Under negative pressure environment, the skin will be deflated, affecting the compensation amount. In this case withrubber compensatorThe skin with good elasticity will do, and the number of layers can be fewer (for example, 2~3 layers), but the sealing performance must be strict. Air leakage from negative pressure flue will directly lead to the decrease of system efficiency.
And guess what? Many maintenance workers complained that "the skin was broken again". When they were removed, the outermost layer was intact, and the middle layer was completely broken-that is, the materials were not selected according to the medium and pressure.
Step 3: Select the number of layers against common configurations-give a few ready-made combinations
Don't be afraid you can't remember, just copy your homework:
- 3-tier standard combination: Silicone cloth + glass fiber cloth + fluorine tape. Applicable scenarios: boiler tail flue, low temperature flue gas, drying kiln. Temperature ≤200℃, no strong corrosion, positive pressure ≤5kPa. Cheap enough.
- 4-layer reinforcement combination: Silicone cloth + glass fiber cloth + PTFE film + fluorine tape. Applicable scenarios: desulfurization flue, chemical tail gas pipeline. Focus on polytetrafluoroethylene film, which can carry strong acid and alkali. FollowDesulfurization flue gas baffle doorMatching expansion joints often use this configuration.
- 5-layer high temperature combination: Silicone cloth + glass fiber cloth + ceramic fiber blanket + stainless steel wire mesh + fluorine tape. Applicable scenarios: cement kiln head, high-temperature area of power station boiler, hot air duct. Note:Metal Corrugated Expansion Joints in Cement IndustryAlthough predominantly metallic, similar multilayer skins are used in the non-metallic compensation section.
attention: A large number of layers does not mean a long life. The key depends on whether the material of each layer is correct. For example, if you use 5 layers, but there is no stainless steel wire mesh in the middle, it will still bulge when pressed.
Step 4: Don't step on pits when installing-the details make or break
If you choose the right skin, it will be useless if you don't fit it well. Keep the following in mind:
- Check flange surface flatness before installation: The skin is a soft connection, and the flange surface is uneven. When the bolts are pressed, the outermost layer of the skin directly presses out the pit, which will leak soon. Take a ruler or gauge and measure it. If it is uneven, level it first.
- Leave sufficient expansion margin: In particularRectangular non-metallic expansion jointWhen installing, the margin of cold tightening or hot tightening must be allowed according to the drawing. Don't deadlift the skin to align the flange. Who is responsible for the crack?
- Disassembly transport screw: Many expansion joints are fixed by transport screws when they leave the factory (to prevent deformation during transportation). Must be removed after installation! This question is related to "Do you need to remove the screw of the expansion joint"That question and answer a truth-if you don't dismantle it, the expansion joint can't be freely expanded and contracted, which is equivalent to white.
- Install rain cover: Non-metallic expansion joint of outdoor flue. Once the skin is exposed to rain, rainwater seeps into the internal layers, and when steamed at high temperature, the interlayers will blister and peel off. Rain covers are cheap, but many people save on them and end up changing the skin every three months.
Two days ago, I met a customer who regarded the transportation screw as a permanent fixture, and the skin was torn after half a year's operation-do you think it was wrong?
Finally, I'll give you a judgment formula
The higher the temperature, the thicker the number of layers, the stronger the corrosion, the more refined the outer layer, and the greater the pressure.Really unsure? Ask the manufacturer for the working condition table and let them customize it according to the actual parameters of your flue-don't blindly make up the number of layers yourself, and the money saved is not enough to change the loss of equipment shutdown.
By the way, if you findSkin layers of flue expansion jointThere are many opinions on this question on the Internet. You might as well compare this guide with the situation at your scene. Pass it one by one, and the answer will naturally be available.