How much can the non-metallic compensator extension joint hold? Don't be fooled by the name
"Is it normal for your non-metallic compensator to telescope and save energy to withstand 300℃?" This question is actually quite in place-many people think that "non-metallic" is soft and temperature-resistant when they hear it. But the reality is just the opposite. The non-metallic expansion joint (also called fabric fiber expansion joint) we often say is mainly pressurized by multilayer composite fabric belts, with aluminum silicate fiber cotton and PTFE membrane sandwiched in the middle, and the long-term working temperature can reach more than 1000℃. Once the metal bellows exceeds 400℃, it has to rely on alloy materials to carry it hard, and the cost will rise. Therefore, it is more cost-effective to use non-metallic ones in places such as boiler flue and hot air duct. Of course, the pressure of this non-metal is indeed weak, and the conventional design pressure does not exceed 0.1MPa. However, if you encounter a low-pressure and large air duct, it is half lighter than metal, so you don't have to worry about flange alignment when installing.
Structure is a "sandwich," but every floor has a statement
The expansion joint of the non-metallic compensator looks like a cloth tube, but when it is actually disassembled, it has at least five to seven layers: the outermost is weather-resistant fluororubber coated cloth, which shields wind and rain; In the middle is a ceramic fiber blanket, which is insulated; The inner layer depends on the medium-polytetrafluoroethylene compensator (PTFE membrane) is used for sulfur-containing flue gas. If it is wear-resistant, add a layer of stainless steel wire mesh. However, there is one detail that many people ignore: the lap seams of the loop must be staggered, otherwise the air leakage rate will double directly. Last year, there was a cement factory project, which used our rectangular non-metallic expansion joint. During the installation, the construction team installed the ring belt in the reverse direction, and as a result, the test run smoked. So don't look at it soft, the installation rules are stricter than metal ones.
Don't just look at the size when selecting the model, the displacement is the key
"Get me a non-metallic compensator expansion joint for DN600." But you have to ask clearly first: Is the pipe axially expanded or laterally offset? The non-metallic compensator expansion joint is best at absorbing lateral displacement and angular displacement. A 1000mm long product can have a lateral displacement of ±100mm, while a metal bellows of the same size may only be ±20mm. Conversely, the amount of axial compression of non-metals is just a cut short. Therefore, in the case of both axial compensation and corrosion resistance, some people string non-metallic expansion joints and general-purpose corrugated expansion joints together-the front absorbs the axial direction and the back absorbs the transverse direction. This trick is particularly common in the flue gas system of the power station industry, but it is necessary to pay attention to leaving enough gaps between the two products, otherwise they will interfere with each other.
Three "death-seeking" actions during installation, and you have to rework if you meet one
Install the guide tube in the reverse direction. The arrow of the guide tube (if any) inside the expansion joint of the non-metallic compensator must be directed toward the direction of media flow. If the medium is installed backwards, it will directly flush the seam of the ring belt, and it will leak in three months. Second: Hoist the loop strap directly with wire rope. The edge of the non-metal loop belt is reinforced by steel belt, but the stress point should be on the flange when hoisting. Many people try to save trouble, and the rope sleeve is pulled as soon as it is hung, and the edge of the loop belt is torn, but it is not admitted. Third: Forgot to leave the amount of pre-stretch. When the manufacturer leaves the factory, it usually gives installation instructions. For example, if you require cold stretching of 10mm, you can directly push it up. When the hot pipe expands, the ring belt will be jacked to death. So whether you use our rubber compensator or fabric fiber compensator, be sure to read the accompanying "installation instructions" note before installation-don't guess from experience.
How many years does the lifespan exist? The standard is not dead, but there is a simple algorithm
The national standard for non-metallic expansion joints JB/T 12235-2015 only says that there is no damage after 1000 times of fatigue test, but does not mention the service life. The actual life depends on three things: the frequency of temperature fluctuations, the corrosiveness of the medium, and the material of the band. For example, the non-metallic compensator behind the desulfurization flue gas baffle door, with the medium containing wet acid below the dew point, is lined with PTFE compensator, which will be fine for five years; However, if the flue gas temperature is tossed back and forth from 80℃ to 200℃ every day, the silicone rubber coating of the ring will accelerate the aging, and it may become brittle in two years. What about that? Simple-every year when the machine is shut down for maintenance, press the surface of the loop belt with your finger to see if there are any cracks; Then use a strong flashlight to shine it from the other side to see through the opaque light. If the light is transmitted, change it quickly. Don't wait for it to leak before repairing it.
Alternative: When should I use a rubber PTFE compensator?
Many people confuse non-metallic compensator expansion joints with rubber PTFE compensators. Rubber PTFE compensator is actually a special case in non-metals. It is lined with PTFE and covered with rubber, which is specially designed to deal with pipelines with strong corrosion, low pressure and normal temperature. For example, for hydrochloric acid pipelines in chemical plants, we can also use our PTFE-lined hoses, but the cost is high; It is half cheaper with a rubber PTFE compensator. But the disadvantages are also obvious: rubber is afraid of ultraviolet rays and ozone, so you have to add a protective cover for open-air clothing. On the other hand, the non-metallic expansion joint of pure fabric fiber is more suitable for high-temperature flue gas-the principle is that the PTFE membrane in the ring belt can resist 235℃, and the ceramic fiber can resist 1260℃, with one section of each tube.