When the skin breaks, the flue leaks-first understand what this thing is carrying
Think about it, what's running in the flue? High-temperature flue gas, sulfide, water vapor, and sometimes dust. The skin of the flue expansion joint is the "soft armor" that blocks the front. If it is broken, the smoke will go out directly, which will not only pollute the environment, but also reduce the efficiency of the fan. Maybe the whole system will have to shut down.
Two days ago, I met a customer who tore a hole in the skin of the flue expansion joint. He asked if he could paste it with tape first. Tsk, can that thing withstand 300 degrees? The skin, which looks like a piece of cloth, is actually a multi-layer composite: the outside is a temperature-resistant layer, the middle is a sealing layer, and there must be a reinforcing skeleton inside. It should not only absorb the displacement of thermal expansion and contraction, but also withstand corrosion and pressure. And guess what? Many faults are caused by choosing the wrong material or saving trouble during installation.
Therefore, the matter of changing the skin really can't be blind. If you follow the following five steps, it will work for at least two or three years.
Step 1: Find out your working conditions and don't buy the wrong materials
Before changing the skin, find out three things:Temperature, medium, pressure。 If these three parameters are wrong, no matter how good the skin is bought, it will be useless.
- Temperature:What is the maximum temperature in the flue under normal operating conditions? Are there any instances of instantaneous overtemperature? For example, at the inlet of desulfurization tower, the flue gas temperature may be about 150℃, but if the boiler bursts, it is normal to rush to 300℃ instantly. When you choose the skin, you have to leave an allowance, at least 50℃ higher than the measured temperature.
- Media:Is the flue clean or raw smoke? Contains no sulfur, contains no moisture? If the wet flue gas after desulfurization is very corrosive, ordinary silicone cloth can't hold it for long.
- Pressure:Positive or negative pressure? The skin of negative pressure system is easy to collapse, so it is necessary to consider adding a guide tube or strengthening the skeleton.
When you are not sure, just take a few on-site photos, measure the flange size (length, width and bolt hole distance), and ask the manufacturer for a plan. Don't just report the model, because different manufacturers have different specifications.
Step 2: Pick the right skin material, silicone cloth or fluorine tape?
There are only a few mainstream flue expansion joint skins on the market: silicone cloth, fluorine tape, polytetrafluoroethylene (PTFE) coated cloth and ceramic fiber cloth. How to choose? Depends on the working conditions.
- Silicone cloth:Temperature resistance about 200℃, good flexibility, suitable for most ordinary flue gas pipelines. The price is also affordable, which is regarded as a "jack-of-all-money". But the resistance to acid and alkali is average.
- Fluorine tape:The temperature resistance can reach 250℃, and the corrosion resistance is one grade stronger than that of silica gel cloth, especially suitable for wet flue gas after desulfurization. However, it is also expensive and hard, so it takes a bit of effort to install.
- PTFE Compensator:It can withstand strong acid and alkali, has low friction coefficient and is not easy to stick to ash. However, the tensile strength is not as good as that of fiber cloth, and it is generally used as an inner lining layer.
- Ceramic Fiber Cloth:High temperature resistance, above 700℃ can be used. But the sealing property is poor, and it is usually used in combination with other coated cloth.
Look at the working conditions of your home-if it's an ordinary boiler flue, silicone cloth is enough; If it is at the outlet of desulfurization tower or after wet dust removal, it is recommended to apply fluorine tape or PTFE compensator. Don't save dozens of dollars, and it will leak in half a year.
Step 3: Preparation before installation, flange cleaning and guide tube do not ignore
This step was overlooked by many people, and as a result, the new skin broke again within a few months of being installed. Why? The flanges weren't cleaned.
After the old skin is removed, there must be residual glue, rust residue and dust on the flange surface. You have to attach wire wheels with an angle grinder and sand the flange surface to a metallic sheen. Then check the flange for any deformation? Are there gaps in the bolt holes? If the flange itself is uneven, your skin will not seal it even if you press it on.
Another forgettable thing —guide tube。 The specific function of the expansion joint guide tube is clearly stated in the FAQ of this site: it guides the flue gas to the center of the pipeline to prevent the high-speed airflow from directly washing the skin. If your flue has an original deflector, check it for corrosion perforations; If not, an additional one is highly recommended. Especially in positive pressure systems, the guide tube can double the life of the skin.
Before installation, spread out the new skin on a clean ground to make sure there are no wrinkles or damages. Don't wait for the flange to find out the wrong shipment, that's a headache.
Step 4: Pay attention to the bolts, and the sequence and torque should not be chaotic
You think you just put the skin on the flange and tighten the bolts? Wrong! Many people's skin leaks, that is, the bolts are not tightened properly.
- Diagonal preload first:Start at the four corners of the flange and screw the bolts, but don't screw them to death, leaving some margin. Then the middle, and then the diagonal tightening. In this way, the skin is evenly stressed and will not wrinkle into a ball.
- The torque can't be too big:The skin is not metal. If it is pressed too hard, it will squeeze the sealing layer. Generally, the torque of M16 bolts is controlled at 80-100N·m. You don't have a torque wrench in your hand? Then it depends on the feel-twist the wrench until it feels hard, and twist it half a turn is enough.
- The beading should be used correctly:Many flue expansion joints have a strip (that is, the metal strip that covers the skin). The bead should be aligned with the flange bolt hole, and it should not be crooked. The function of the pressing strip is to compress the skin evenly and prevent the screw from piercing the skin directly.
Bolts should be coated with anti-rust oil, especially in wet smoke environment. Otherwise, the next time you change the skin, the bolts are rusty and can't be removed, which is called a collapse.
Step 5: Daily maintenance, the soil method to make the skin last for two more years
Leave it alone when the skin is installed? Then it may not last for a year. But if you have a little bit of a snack, two or three years will be fine.
First, check it regularly. Once a month, use a flashlight to show whether the skin surface is bulging, cracking or hardening. Especially when spring and summer change, the temperature and humidity change greatly, and the skin is most prone to problems.
Second, keep the flue from dust accumulation. Too much dust presses on the skin, and it will crush the skin over time. Especially when using the rectangular non-metallic expansion joint of this station, ash hopper should discharge ash frequently.
Third, if you find a small damage, make it up quickly. There are special silicone repairing agents on the market, which can be carried for a while with a small mouth. But don't expect the repair to last a year, that's an emergency-it's the right way to stock up and prepare for new ones.
Fourth, if the ambient temperature is too high, consider adding a layer of insulating aluminum foil on the outside of the skin. Don't underestimate this layer of aluminum foil. It can reflect radiant heat and reduce the skin temperature by 20 or 30 degrees.
You ask me how long does the skin last? That depends on the working conditions and maintenance. Some people are fine after five years of use, while others are wasted after one year of use. But there is one thing: don't wait until the smoke is out to change. If you find a crack, you have to check it and pinch the problem in the bud.
Okay, all five steps are here. From understanding the working conditions to material selection, installation and maintenance, you have understood these steps thoroughly, and you can do it yourself when you encounter the skin problem of the flue expansion joint in the future.