Let's talk about something first: how to cure the "old problem" of power plant flue?
I used to encounter a power plant project, and the flue interface always leaked. The original design used a metal expansion joint, but it couldn't withstand the corrosion of high temperature and sulfur-containing flue gas, and it was scrapped in a few months. When I removed it, I saw that the bellows was covered with pitting corrosion and perforated in some places. Later replaced withStainless steel round non-metallic compensatorThe problem is completely solved. What's the difference between these kinds of products? To put it bluntly, it is a combination of a stainless steel frame and a flexible non-metallic loop belt-the frame provides structural strength, and the loop belt is responsible for absorbing thermal displacement and damping vibration. Compared with pure metal, it is not afraid of chloride ion corrosion, and it will not cause fatigue cracks due to frequent displacement. And guess what? It's been almost three years since I changed it, and I haven't leaked at all.
Structural anatomy: stainless steel frame + multi-layer "soft armor"
The circle band of stainless steel round non-metallic compensator is not as simple as a layer of cloth. It is usually composed of multi-layer composite materials, including fluororubber, polytetrafluoroethylene, ceramic fiber, etc. The laminated design takes into account both sealing and temperature resistance. The outer layer is fixed with stainless steel flanges or clamping rings and connected to the pipe. Note that "stainless steel" here refers to the frame and fastener materials. Not the whole compensator is metal-the loop band is the core. Some manufacturers like to call it "fabric fiber expansion joint", which is actually a kind of thing. We have the corresponding product information in our station — —Non-metallic expansion joint (fabric fiber expansion joint), described in greater detail.
The inner layer of the loop is usually made of polytetrafluoroethylene film as an anti-corrosion insulation layer, with a ceramic fiber blanket sandwiched in the middle for heat insulation, and the outer layer is coated with fluororubber or silicone rubber to ensure airtightness. This "sandwich" structure can easily cope with smoke within 300℃. If a higher temperature is needed, the belt material has to be replaced with aluminum silicate fiber layer, and the temperature resistance can be above 600℃.
Where on earth is it used? Don't just think about the flue
The most common application scenario is the flue gas pipeline system, especially the working condition with desulfurization. The flue gas contains sulfide and water vapor, and the temperature is around 200℃, so the metal bellows is easily pitted. With stainless steel round non-metallic compensator, the ring belt is acid-resistant, does not accumulate dust, and can also adapt to the deviation of large diameter pipeline. Fan outlets in cement industry and cold air ducts in power stations are also common. In addition, cooperating withRound flapper doorOrManual plug-in insulation doorWhen in use, it can effectively isolate vibration transmission. Has any customer loaded it at the inlet of the coal mill? Works just as well because pulverized coal pipes also need to be resistant to wear and absorb displacement.
But don't forget, this stuff is not a panacea. Extreme high pressure (e.g. above 1.6MPa) or vacuum conditions, the ring belt will be deflated or bulged, and at this time it has to be returned to the metal compensator, such asMetal rectangular expansion jointOrDirect buried (fully buried) type expansion joint。 The core of selection is to understand the core contradiction of one's working condition.
Pit with the largest selection: displacement, not caliber
Many purchases ask "how big is the caliber and how high is the pressure". Actually, where is the real pit? The amount of displacement. Non-metallic compensators can absorb axial, lateral, and even angular displacements, which are larger than metallic ones, but only if the number of layers and materials of the band are selected correctly. Temperature and medium are hard indicators-for example, above 300℃, conventional fluororubber will not work, and aluminum silicate fiber will be obtained. Also, the bolt material of the flange should be stainless steel, otherwise rust will lead to leakage over time. You can refer to the "National Standard for Non-metallic Expansion Joints" JB/T 12235-2015 of this site, which specificates the test methods in detail, such as tensile strength, compression test and airtightness test of loop belts.
The year before last, I helped a cement factory to select a type. The fan outlet diameter is DN1200, the temperature is 280℃, and the displacement requires 30mm in the transverse direction and 50mm in the axial direction. According to the conventional selection of fluorine rubber ring belt is definitely not enough. Later, aluminum silicate fiber + PTFE composite layer was used, and the ring belt was made of 5 layers. The margin of the tie rod stroke was also reserved, so it was completely fine to run for one and a half years. Is that the truth? The selection must be calculated by taking out the working condition parameters, and you can't pat your head.
What are you most afraid of when installing? The tie rod nut is not adjusted, and the guide tube is installed backward
More attention should be paid to when installing, and the pull rod and nut must be adjusted in place. The main function of the expansion joint tie rod is to limit excessive stretching. Before installation, the tie rod nut must be loosened to the design stroke, otherwise it will not work at all once the equipment is started. How exactly to adjust? We had previous FAQ"How to adjust the tie rod nut of the expansion joint"It is very clear in it. And the guide tube-if any-never install it backwards, the direction of the arrow represents the direction of the medium flow. In the past, a customer welded the deflector backwards, and the ring belt was directly broken. It cost hundreds of thousands of yuan to shut down once it was changed. The function of the guide tube is to guide the medium to flow smoothly through the inside of the compensator, so as to reduce the scouring of the ring belt by turbulence. If it is installed backwards, it is equivalent to leading the medium to the back of the ring belt to impact.
In addition, when installing, there must be fixed brackets and guide brackets at both ends of the compensator, otherwise the thermal expansion of the pipe will pull off the compensator. Don't ask me how I know-the pilot frame was not made on site, and the flange weld cracked in about half a year.
At the end of the day, cost performance is the last word
Therefore, on the whole, stainless steel round non-metallic compensator has advantages over metal in terms of cost performance, especially suitable for large diameter, low pressure and high temperature corrosion pipelines. If the project budget is limited and you want to worry about it, it's 80% right to go directly. Of course, extreme high voltage or vacuum conditions have to return to the metal compensator ordirectly buried expansion jointTo choose. Only by understanding the core contradictions of your own working conditions can you choose the right product.
We also have a lot of relevant product information in our site, such asDesulfurization flue gas baffle door、Metal Corrugated Expansion Joints in Cement IndustryAll are paired with the compensator. If you have a project on hand, you may wish to send the working condition parameters, and we can calculate the displacement and the number of belt layers together. Feel free to contact a technical consultant directly.