Non-Metallic Expansion Joint Disadvantages? Don't wait until you leak to understand these pits. After more than ten years of pipeline compensation, I have seen too many projects stumble on non-metallic expansion joints-it is not that it is bad, but that many people only focus on its advantages of cheap and large displacement resistance, and throw its shortcomings behind them. Today, if you don't brag or black, explain these pits clearly one by one.
Pressure capacity is a flaw
The core structure of non-metallic expansion joints (fabric fiber expansion joints) is a fiber fabric composite layer plus a metal frame, which is subjected to pressure by flexible bands? Thinking too much. Its pressure-bearing skeleton is essentially a fiber cloth and sealing layer, not a rigid metal shell. When the pressure is slightly higher, the circle belt will bulge like blowing a balloon, and if it is higher, it will tear directly.
In practical applications, non-metallic expansion joints can usually only be used in pipeline systems below 0.1MPa, and many smoke and air duct working conditions even only have a micro positive pressure of several thousand Pa. Compared with the metal corrugated expansion joint, the stainless steel corrugated pipe can easily carry 1.6MPa, and the special corrugated expansion energy saving for high-pressure steam pipeline can achieve more than 10MPa. And guess what? Someone dared to install a non-metallic expansion joint on the compressed air line, but the loop belt burst after half an hour of turning on. Have you ever seen a pressure cooker seal with canvas? No, no.
Temperature resistance is not infinite
The limit of fabric fibers lies there. The long-term temperature resistance of conventional silica gel-coated glass fiber products is ≤250℃, fluororubber ≤200℃ and polytetrafluoroethylene ≤150℃. Even if it is compounded with high silicon oxygen or ceramic fiber, and the limit is about 1000℃, it is also a special customization, and the cost is high. If it runs at a temperature close to the upper limit for a long time, the fiber will gradually embrittle and powder, and finally leak.
Two days ago, I met a buddy from a cement factory. The outlet temperature of the high-temperature fan frequently rushed above 900℃, and there was no margin left in the design. The non-metallic ring belt was ablated like a ragged rag in less than a year, and the scene was terrible. Therefore, leave at least 20% of the temperature margin when selecting the model, and don't take the upper limit as a normal working condition.
Easy to corrode and wear? Sulfur, chlorine, and dust in the medium are all enemies
In scenes such as flue gas baffle door and desulfurization flue gas baffle door, the non-metallic belt is not faced with clean air, but a mixture containing SO₂, chloride ions and high humidity acidic gas. Once the acid penetrates into the fiber layer, it directly corrodes the internal metal frame and connecting bolts. Dusty airflow washes at high speed, and the surface of the ring belt is like sandpaper polishing, and it is worn through from the weak point first.
Surface peeling → fiber fracture → perforation leakage. In a desulfurization project, acid-resistant coating belt was not used in order to save money. Half a year later, the belt was rotten like honeycomb briquettes, the baffle door was not closed tightly, and the whole system had serious air leakage. If there is sulfur, chlorine and dust in the medium, you have to choose the corresponding corrosion-resistant and wear-resistant composite layer. Don't think that all non-metallic expansion joints are the same.
Installation and replacement are not that simple
Many people think that non-metallic expansion joints are flexible, so they can be installed casually. Wrong! Precisely because of its softness, it has more demanding requirements for pre-stretching and limiting than metal expansion joints. Rectangular non-metallic expansion joints and round non-metallic expansion joints must be adjusted according to the designed cold drawing value when installing-the cold drawing amount is not enough, there is no compensation margin in the hot state, and the ring belt is pulled and cracked; The amount of cold drawing is too large, and it is squeezed into wrinkles when it is cold, and it doesn't take long to wear out.
The limit screw and the transport fixture should not be disassembled blindly. Some on-site workers try to save trouble. As soon as they come up, they screw off all the limit bolts. As soon as the pipeline expands slightly, the ring belt directly tears open a big hole. After the installation is completed, the adjustment of the limit device should be adjusted, and the removal of the limit device should be removed according to the manufacturer's instructions. Flexibility is not casual, but more demanding.
Lifespan Anxiety: Exactly How Many Years Will It Last?
There is no uniform answer to this question, but it varies greatly. Clean air, temperature no more than 150℃, no corrosive medium, it is normal to use for 5 to 8 years; However, if the medium contains sulfur and dust, and the temperature fluctuates frequently, it is not uncommon to leak in 1 to 3 years. The key lies in selection and maintenance.
Select the material and structure of the ring belt according to the pressure, temperature and media composition during the selection, strictly pre-stretch and limit the position during installation, and regularly check the surface of the ring belt for wear, blister and hardening during operation. Don't wait for a leak to pat your thigh. At that time, you can only stop the furnace for emergency repair, and the loss is dozens of times more expensive than the expansion joint itself.
Where is there a perfect compensator? In high-pressure working conditions, metal corrugated expansion joints are honestly selected, and it is the turn of non-metal expansion joints to play in large displacement and low-pressure scenarios. Understanding the shortcomings is not to deny it, but to use it for a long time.