Just say the answer: What exactly is the common temperature tolerance range?
The temperature resistance limit of high-temperature non-metallic expansion joints is not a fixed value, but depends on which fiber material you choose. The mainstream high-temperature non-metallic expansion joints on the market (that is, we often call fabric fiber expansion joints) mainly use three kinds of fabrics:
- Silicone cloth: The continuous working temperature is generally around 250℃, and it can reach 300℃ instantly. Suitable for ventilation ducts with low flue gas temperature, such as boiler tail flue.
- Fluorine tape: The temperature resistance can reach 300℃-350℃, and the corrosion resistance is stronger than that of silica gel cloth. Fluorine tape is the first choice when it comes to flue gas containing sulfur and acid.
- Ceramic fiber cloth: This is the real high temperature resistant player. The limit temperature can be above 1000℃, but in actual engineering, we generally design according to 800℃-1000℃. The ceramic fiber itself is fine with temperature resistance, but the outer sealing layer (such as the silicone rubber coating) will limit the overall temperature resistance.
Many manufacturers name "temperature resistance 1200℃", but you have to ask whether it is a short-term peak or a continuous working condition. We have done a case in the power station industry-the flue temperature of a power plant is designed to be 850℃, and we chose ourNon-metallic expansion joint (fabric fiber expansion joint)The inner layer is made of ceramic fiber felt + multi-layer insulation layer, and the outer layer is made of high-temperature resistant coating. At present, it has been in stable operation for 3 years. The temperature parameter does not depend on how much it can carry at the highest, but whether it can carry "continuous drying".
Three "Invisible Killers" Affecting Temperature Resistance
Just because the temperature number looks good doesn't mean it can be used. I have encountered it several times, and the customer took the parameter of 800℃ to select the model, but the result was leaked in less than half a year. Why? Because temperature is only a basic indicator, these three things are really fatal:
Medium corrosivity
High-temperature flues often carry sulfur dioxide, hydrogen chloride, and even alkali vapor. Ceramic fiber can withstand 1000℃, but encounter strong acid corrosion, the fiber structure will be destroyed. At this time, you have to choose fluorine tape or add corrosion-resistant coating. weDesulfurization flue gas baffle doorThe matching non-metal expansion joint, the lining is made of polytetrafluoroethylene film to prevent corrosion.
Pressure fluctuation
The fabric layers of non-metallic expansion joints have no strength themselves and rely on metal frames and platens. Once the pressure exceeds the design value (generally, the design pressure of non-metallic expansion joint does not exceed 0.1MPa), the fabric will bulge or even tear. The higher the temperature, the faster the tensile strength of the material decreases. For example, the strength of the same silicone cloth is about 60% of that of normal temperature at 200℃, but it may only remain 30% at 300℃. So don't just look at temperature, pressure and temperature should be calculated together.
Number of cyclic displacements
The high-temperature non-metallic expansion joint compensates for thermal expansion and contraction, and every time the unit starts and stops, it is a large displacement. Fibrous materials are subject to fatigue aging under repeated bending. We have a customer in the cement industry. The kiln tail pipeline uses ordinary non-metallic expansion joints, which are replaced twice a year. Later, we put on oursMetal Corrugated Expansion Joints in Cement Industry(Strengthened design is made for high temperature and multi-displacement working conditions), and the service life is directly doubled.
Non-Metallic Expansion Joints vs Metallic Expansion Joints: Who is More Reliable?
When many engineers hear about high temperature, their first reaction is to "put on the metal expansion joint". However, the metal expansion joint also has shortcomings at high temperature: the bellows will cause fatigue cracks due to thermal stress, and the installation accuracy is extremely high. OurHigh temperature axial expansion jointIt performs well below 600℃, but when it exceeds 700℃, nickel-based alloys have to be used, and the cost will rise.
Low cost, light weight, large amount of compensation and good corrosion resistance。 Especially in the scenario of large-diameter flue (more than 2 meters in diameter), using metal expansion joints is not only expensive, but also a problem in manufacturing and transportation. Non-metallic expansion joints can be assembled on site, and the maintenance is simple-if they are broken, only the fabric loop belt is changed, and the pipe is not removed.
Then when to choose non-metallic? Remember two principles: one is that the temperature is high but the pressure is low (Corrugated expansion joint for power station industryIt is used a lot at the outlet of the boiler (temperature 500-600℃), but at the inlet of the desulfurization tower (temperature 120-180℃, containing corrosive flue gas), the non-metallic expansion joint is the optimal solution.
The easiest pits to step on when selecting a model
Pit 1: "All non-metals are resistant to 800℃"
This is the biggest misconception. You take a silicone cloth to carry 800℃, and it will burn to ash in less than an hour. Only ceramic fiber substrate is resistant to 800℃, and multi-layer insulation layer must be designed: inner ceramic fiber blanket, middle fire barrier layer and outer sealing cloth. Without any layer, the temperature parameter is waste paper.
Pit 2: Ignore the insulation design
The insulation of non-metallic expansion joints is not just stuffed with asbestos. We doRectangular non-metallic expansion jointWhen, the insulation layer thickness is calculated according to the flue section and the temperature gradient. For example, the flue temperature is 600℃, and the external surface temperature is required to not exceed 60℃. The thermal insulation layer must be at least 150mm thick, and multi-layers of staggered seams should be laid to prevent thermal bridges.
Pit 3: Ignoring the air or water cooling requirements of the installation location
Some high-temperature pipes are close to the steel structure, and radiant heat can bake the peripheral equipment. At this time, it is necessary to install an air-cooled jacket or a water-cooled jacket. We encountered a machine in the cement industryMetal Corrugated Expansion Joints in Cement IndustryAlthough the metal part itself is fine, the adjacent non-metallic compensator causes the fabric to age prematurely because there is no ventilation gap. Later, an air guide hood was added, and the problem was solved.
High Temperature Application in Power Station, Cement and Desulfurization
- Power station industry: The temperature of the boiler flue is usually 400-600℃, ourCorrugated expansion joint for power station industryUse with non-metallic compensators. The non-metallic part is used between the outlet of the induced draft fan and the desulfurization tower, and the temperature drops to 120-180℃, but contains SO2 and dust. It is used with fluorine tape + wear-resistant lining plate, and the life span is 3-5 years.
- Cement industry: The temperature of the kiln tail exhaust gas is as high as 900-1000℃, but the pressure is extremely low (slightly negative pressure), and there is a lot of alkaline dust. At this time, non-metallic expansion joints are the only option. We made it for a cement factoryMetal Corrugated Expansion Joints in Cement IndustryIn fact, it is used for the circulation pipeline of raw mill (temperature 150℃), and the kiln tail is the world of non-metals. Note: High-temperature non-metallic expansion joints in cement industry must have wear-resistant guide tubes, otherwise dust directly washes the fabric layer, and it will be perforated in half a year.
- Desulfurization industry: This scenario is the most complex-the temperature is not high (80-150℃), but the medium is a strongly corrosive slurry or wet flue gas. Metal expansion joints can't withstand pitting corrosion with 316L, while non-metallic expansion joints have a longer life because they are lined with PTFE or rubber. OurDesulfurization flue gas baffle doorThe matching non-metallic expansion joint is designed with a liquid drainage port at the bottom, which solves the problem of liquid accumulation corrosion.
Summary: The selection checklist behind the high temperature numbers
At this point, you should understand:How many degrees is the high temperature of the high-temperature non-metallic expansion jointNot a simple number, but a set of working condition matching logic. Keep these three in mind:
- Look at the media: Smoke or hot air? Does it contain corrosive ingredients? Decide to choose silicone cloth, fluorine tape or ceramic fiber.
- Look at displacement: Use non-metal when the displacement is large and the frequency is low; Use metal when displacement is small and pressure is high. Don't mix it.
- See attachment: The thickness of the insulation layer, the cooling method, the anti-corrosion lining these details determine success or failure.
Selection is not about whose parameters are bright, but about who runs longer. Next time I see the advertisement of "Temperature Resistance 1000℃", let me ask first: What is the continuous temperature? How much pressure? What are the ingredients of media? — — After asking these three questions, the manufacturer will know that you are an expert.