How many degrees can a non-metallic expansion joint carry? Give me a hard target first
"What is the temperature resistance of non-metallic expansion joints? The temperature of my flue gas pipe here is 350℃, can it be used?" This question is asked almost every week, but the answer really can't be dispatched with a "can" or "can't" sentence. Non-metallic expansion joint (also called non-metallic compensator, this site has specialNon-metallic expansion joint (fabric fiber expansion joint)The temperature resistance range of the product mainly depends on its "skin"-that is, what material is used for the skin and filling layer. The most basic hard index: the upper limit of temperature resistance of conventional products is about 400℃, but the gap can be stretched several times for different materials.
Think about it, the temperature of the flue of a power station boiler may rush to more than 600℃, while the ordinary air conditioning pipe is only dozens of degrees. There is no "universal" non-metallic expansion joint, only the "right road" selection.
Material determines the upper limit: fabric fiber, rubber, PTFE, temperature resistance is different
The "body" of non-metallic expansion joints is usually composed of multi-layer composite materials, the core of which is the skin. There are three common categories:
Fabric fibers (silicone cloth, fluorine cloth, ceramic fiber cloth)
This is the most common non-metallic expansion joint material. The long-term working temperature of silicone cloth skin is-60℃ ~ +200℃, and the short-term working temperature can reach 250℃; Fluorine tape is more manufactured, generally at-20℃ ~ +300℃, and the special formula can reach 350℃. If you encounter high-temperature smoke, you have to use ceramic fiber cloth, which can be temperature-resistant and dry directly above 1000℃, but the price will double several times. We have quite a fewRectangular non-metallic expansion jointIt is laminated with multiple layers of ceramic fibers, and is specially equipped with boiler flue. To put it bluntly, fabric fiber expansion joints are the best "elastic" and can absorb large displacements, but the upper limit of temperature resistance depends on the fiber material.
Rubber (EPDM, NBR, silicone rubber)
rubber compensatorIt relies on elastic deformation to absorb displacement, which is cheap and hassle-free to install. However, rubber is naturally afraid of high temperature: the upper temperature resistance limit of nitrile rubber (NBR) is about 100℃, EPDM (ethylene propylene monomer) can reach 150℃, and silicone rubber can reach 200℃. Higher? The rubber will age, become brittle and crack. Therefore, rubber non-metallic expansion joints are usually used in air conditioners, water systems and low-pressure steam pipes, and no one dares to stuff them into the flue of power stations. In addition,Rubber PTFE compensatorIt is a composite of rubber and PTFE, and its temperature resistance is between the two, but it emphasizes corrosion resistance.
Polytetrafluoroethylene (PTFE/PTFE)
PTFE compensatorIt is the "king of corrosion resistance", and it is not afraid of strong acids and alkalis, but the upper limit of temperature resistance is about 250℃ (long-term), and it can reach 280℃ in the short term. The disadvantages of PTFE are that it is not resistant to wear, will soften at high temperature, and has poor elasticity. It mainly relies on corrugated structure to compensate for displacement. If your pipeline is filled with high-temperature and highly corrosive media (such as wet flue gas behind the desulfurization tower), tetrafluorine is the optimal solution-seeDesulfurization flue gas baffle doorPTFE-lined expansion joints are commonly used in systems.
Don't just look at temperature: pressure, medium, displacement are all holding back
Do you choose the right material and everything will be fine? It depends on whether the working conditions are "giving face". For example: a fabric fiber expansion joint has a nominal temperature resistance of 350℃, but if the pipeline pressure soars to 0.3MPa, the medium is high-speed dust flue gas, and the lateral displacement per hour exceeds 50mm-then the actual allowable working temperature may be discounted by 30%. Why? Because the strength of the material decreases at high temperature, the skin is easy to bulge or tear when the pressure comes up. If the displacement is too large, the fiber layer will be excessively fatigued and the life will be sharply reduced.
To put it bluntly, the selection formula is:Actual operating conditions = temperature + pressure + medium corrosivity + displacement + cycle frequency。 Not even one less. For example, those used in the power station industryCorrugated expansion joint for power station industry(Metallic) is more stable at high temperatures and pressures, while non-metallic has the advantage of vibration reduction and large displacement absorption, both of which perform their respective duties. If you have to take a rubber compensator with a temperature resistance of 200℃ to carry the hot air duct of 300℃, that's not a mistake in selection, but looking for trouble.
How to choose high temperature working conditions? Real cases from flue gas baffle doors to power station boilers
In the original flue gas pipeline of the desulfurization system of a power plant, the temperature fluctuates between 180℃ and 230℃, the pressure is very low (slightly negative pressure), and the medium contains a large amount of SO₂ and condensate acid. The customer initially chose the ordinary fabric fiber expansion joint, but it was leaked in half a year. Later replaced withFlue gas baffle doorcomplementaryNon-metallic expansion joint (fabric fiber expansion joint)The skin is lined with double-layer fluorine tape + polytetrafluoroethylene, and an aluminum silicate cotton insulation layer is added in the middle. This combination is temperature-resistant, corrosion-resistant and can absorb heat displacement, and there has been no problem for almost three years now.
The air inlet of the rotary kiln in the cement industry has a long temperature of 400℃ ~500℃, and a large amount of dust is carried with it. At this time, only non-metallic expansion joints mainly made of ceramic fiber cloth can be used, and a guide tube must be installed (refer toMetal Corrugated Expansion Joints in Cement IndustryFlow diversion design) to protect the skin from being washed by high-velocity particles. You see, the devil is in the details.
There is also the flue at the tail of the boiler, which is usually at about 300℃, but the space is limited and requires a large lateral displacement. At this timeRectangular non-metallic expansion jointIt is more fragrant than metal-light weight, flexible installation and better ability to absorb displacement. However, remember to choose a flame-retardant skin. In case the boiler deflagrates, ordinary fabrics will burn through.
Improper installation and maintenance, no matter how high the temperature resistance is, it is useless
The last one, many people ignore. When the non-metallic expansion joint is bought, the installation is misaligned, the bolt torque is uneven, or there is not enough pre-compression, which will cut the actual life by half. Such asUniversal corrugated expansion jointThe (metal) tie rod nuts need to be adjusted after installation, and the non-metal ones have similar problems. How exactly to adjust? You can refer to the information in our site"How to adjust the tie rod nut of the expansion joint"That Q&A.
Regularly check the skin for scratches, bulging or chemical corrosion marks, paying particular attention to leakage at the flange joints. If the skin is found to be partially worn, it can be repaired by hot pressing with the same material patch. Don't wait until it is completely replaced. Also, don't forgetexpansion joint guide tubeFunction-it not only diverts flow, but also protects the skin from being blown directly by high-temperature smoke. Don't reverse the installation direction of the guide tube when disassembling and assembling.
Is it OK to use non-metallic expansion joint for 350℃ flue gas pipeline? The answer is: as long as you choose the right fabric fiber (such as fluorine tape or ceramic fiber cloth), with a reasonable insulation layer and diversion structure, it is completely fine. But if you only buy ordinary silicone cloth for cheap, then it won't work. Therefore, there is no standard answer to "how much is the temperature resistance of non-metallic expansion joints", the only criterion is your working condition parameters.