Find out the "temper" of your house's clean flue first-temperature, corrosive substances and pressure are indispensable
Before choosing a skin, you have to find out at least three things: how high the temperature is, whether there are corrosive components in the smoke, and how much pressure is in the pipe. As long as these three figures are one difference, no matter how good the skin is, it will not be able to carry it. Two days ago, a customer came up and asked, "I want the most expensive fluororubber". As a result, when he asked, the flue gas temperature on his side was above 350℃ all the year round, and the temperature resistance limit of fluororubber was only about 250℃. Isn't this a waste of money?
How to touch? Three steps:
The first step is to check the design drawings or measure the surface temperature of the flue with an infrared thermometer on the spot, leaving a safety margin of 10% ~20%. For example, the actual 300℃, then when you choose the skin, the temperature resistance must be at least 360℃. The second step is to check whether there are acidic gases such as SO₂ and HCl in the flue gas, or whether there is oil mist and dust. The more corrosive, the higher the chemical resistance requirements of the skin. The third step is to confirm the working pressure. Generally, the net flue is slightly negative pressure or low pressure (≤0.1MPa), but if there is a positive pressure section, the pressure bearing capacity of the skin has to keep up.
If you are not sure, just turn over the product information of "Non-metallic Expansion Joints (Fabric Fiber Expansion Joints)" on this site, which generally lists the applicable working conditions, and just check it.
How to pick the skin material? Silicone, fluoroadhesive or PTFE? Compare the product list of this site to select
To put it bluntly, the skin is a few layers of cloth + coating pressed together. There are three common coating materials: silicone, fluororubber, and polytetrafluoroethylene (PTFE). Let's talk about it one by one.
- Silicone skin: Temperature resistance range-60℃ ~250℃, good elasticity, good sealing performance, but average acid and alkali resistance. It is suitable for occasions where the smoke is clean and the temperature is not high.
- Fluorine rubber skin: The maximum temperature resistance is about 250℃, oil resistance, acid and alkali resistance are much stronger than silica gel, and the price is also a bit more expensive. Be sure to make sure that the temperature does not exceed the limit before selecting it.
- Polytetrafluoroethylene (PTFE) skin: It can be carried to 260℃ for continuous use, and it can reach above 300℃ in a short time, and it hardly reacts with any chemical substances, and it is corrosion-resistant ceiling. The disadvantage is that it is stiff and poor elastic, so you have to be extra careful when installing it.
Then which one to choose? A stupid way: open the product page of "Non-metallic Expansion Joint (Fabric Fiber Expansion Joint)" on this site, and put the working condition parameters into it to see which one has a high matching degree. In addition, the "rubber compensator" and "rubber PTFE compensator" of this site are often used in similar scenarios, but note that their upper temperature resistance limit is usually not as good as that of pure PTFE. Really entangled, go directly to customer service and drop a sentence: "I am a clean flue, the temperature is XX, the corrosive substances are XX, and the pressure is XX", and let them recommend it.
3 details that are most prone to rollover when installing a skin: sealing, pre-stretching, bolt torque
The installation looks simple, but the rollover rate is really not low. One of the worst cases I have ever seen: the worker screwed the bolt so hard that the skin tore straight away-strangled to death. Remember three key points:
1. The seal must be tightly fitted.Check the flange surface before installation, whether there are burrs, rust and welding slag? If you have it, dispose of it first. A sealing gasket (usually asbestos rubber sheet or PTFE pad) should be placed between the skin and the flange, so as not to save trouble and confront it directly.
2. Do not forget pre-stretching.When the new skin is installed, give a pre-stretch amount. Why? Because the pipeline expands and contracts by heat, if it is not pre-stretched, the skin will be tightened as soon as the temperature comes up, and the life will be directly discounted by 50%. How much exactly? Referring to the provisions of National Standard for Non-metallic Expansion Joints JB/T 12235-2015, it is generally extended by 1% ~3% of the installation length. You can install the bolt on one side first, and gently pull the skin to the specified length with a tool on the other side before fixing it.
3. The bolt torque should be uniform.Don't screw to death all at once! Gradually tighten in 2~3 passes along the diagonal. For the torque value, see the manual of the skin manufacturer. If not, refer to the M16 bolt torque, which is about 80~120N·m. If it is too loose, it will leak, and if it is too tight, it will crush the skin directly. I am used to twisting to the point that "I can't turn my fingers no matter how hard I push them" and then backing back half a turn-pure experience, try it for yourself.
How to do daily inspections? Keep an eye on these 5 parts, and the skin life can last two years longer
The skin is not installed and done. If you take a look at it regularly, many problems can be found earlier. When you inspect, focus on these five places:
- Welds and flange edges: Are there any cracks or bulges? Especially at the connection between the skin and the flange, the stress concentration is easiest.
- skin surface: Is there any bubble, delamination, hardening? Touch it with your hand. If it feels obviously brittle than when it was new, it means that the material is aging.
- Strips and bolts: Is there any deformation in the strip? Are the bolts loose? Try twice with a wrench, don't really tighten it, just check it.
- Deflector (if available): As mentioned in the "Specific Function of Expansion Joint Guide Tube" of this site, the guide tube protects the skin from being directly washed by airflow. During the inspection, see if the guide tube is worn or washed away.
- drainage hole: There are drainage holes at the bottom of some net flue expansion joints, so don't block them. Blocking the standing water will accelerate skin corrosion.
Once a week for the first month of new fitting, then changed to once a month. Just like doing maintenance on a car, it never hurts to be diligent.
Don't panic if your skin is broken! Emergency Repair and Replacement Steps
What if it's broken? Look at the mouth size. Small cracks less than 5cm-emergency repair; Widespread rupture – replace straight away. Let's not talk clichés, just go to dry goods.
Emergency repair (small break)
Preparation tools: high temperature silicone rubber (temperature resistance 300℃ +), fiberglass cloth, scissors, brush.
Step:
1. Wipe the dust and oil around the break and degrease it with alcohol or acetone.
2. Cut a piece of fiberglass cloth that is more than 5cm larger than the break.
3. Brush a layer of silicone rubber on the break and fiberglass cloth, stick it, compact it by hand, and discharge bubbles.
4. Wait for 24 hours to cure before turning on (the higher the temperature, the faster the cure).
Note: This is only a temporary measure and it is best to arrange a formal replacement within two months.
Official replacement
This standard stipulates the whole process of installation, inspection and acceptance. I'll just talk about the key steps:
1. After shutting down and cooling down, remove the strips and bolts of the old skin.
2. Check the flange surface. If there is corrosion, it must be polished or replaced.
3. Before installing the new skin, pre-stretch it according to the standard requirements (as mentioned earlier).
4. Tighten the bolt torque according to the design value, and tighten it diagonally in 3 passes with a torque wrench.
5. Do the airtightness test after installation. The national standard requires that 0.05MPa compressed air be kept under pressure for 5 minutes, and no leakage is considered qualified. If the net flue pressure is low, you can also brush the joint with soapy water to detect leaks.
Don't be cheap and buy three no skin. The "non-metallic expansion joint (fabric fiber expansion joint)" products of this site are all produced according to the national standard, and at least there is a guarantee. You don't want to just replace it and break it, do you?