Two days ago, a customer who was doing a desulfurization project sent a drawing, which was clearly marked "Non-metallic Compensator Type A". He asked me: Lao Zhang, is this the same thing as the non-metallic expansion joint (fabric fiber expansion joint) in your shop? I said, don't be confused, this is the same thing, but the code name on the drawing is different. Type A non-metallic compensator, to put it bluntly, is the most basic round fabric fiber expansion joint.
Let's talk about the conclusion first: Type A is not mysterious, it is a round fabric fiber expansion joint
Talking about non-metallic compensators in the industry, there are two main categories: fabric fiber expansion joints and rubber compensators. Type A specifically refers to a circular structure with single or multi-layer fabric bands, flanged connections, and no guide tubes. Without those bells and whistles configurations, the structure is the simplest and the price is the most affordable. If you take over a flue gas pipeline project, you only write "Non-metallic Compensator Type A" on the drawing, without additional parameters such as pressure, temperature and guide tube. You can't go wrong with the standard parameters of "Non-metallic Expansion Joint (Fabric Fiber Expansion Joint)" of this site to quote.
Look at the structure: the three core components, the circle belt is the soul
The A-type body consists of three things: a loop (that is, a layer of fabric fibers), a metal flange, and a compression bolt. The loop belt is made of silicone or fluororubber coated cloth, glass fiber cloth and ceramic fiber cloth, and has a temperature resistance range of-40℃ to 400℃. It does not absorb the displacement by the deformation of the metal corrugation like the metal corrugated expansion joint, but by the flexible bending of the ring belt itself. This brings a huge benefit – the thrust on the pipe is so small that it is almost negligible. Is it much gentler than the universal corrugated expansion joint of metal?
The number of layers and thickness of the loop belt determine its temperature and pressure resistance. Under normal standard working conditions, three to four layers of composite are sufficient. In case of highly corrosive fumes, a fluororubber coated cloth must be arranged. The price will be a little more expensive, but the lifespan can double.
So what is the difference between it and Type B and Type C?
Type A is the basic model, Type B is the strengthened model, and Type C is the anti-pressure model.
- Type A: The most basic single-loop belt structure, suitable for low pressure (≤0.1MPa) and small displacement scenarios. Air duct, flue duct and dust collection duct are its home field.
- Type B: Install heat insulation layer or guide tube on the A-type basis. The function of the guide tube is to guide the high-temperature flue gas to directly scour the ring belt, so as to avoid the flame directly contacting the fabric layer. Type B is more reliable in high-temperature occasions such as cement kiln tail waste gas pipeline and boiler outlet.
- Type C: Add a stainless steel wire mesh reinforcement layer outside the A-ring belt to resist positive pressure conditions. For example, the pressure of the flue behind the flue baffle door may reach 0.15MPa, and Type C can hold it.
But don't get confused. The "non-metallic expansion joint (fabric fiber expansion joint)" of this site is the standard form of Type A. The "rectangular non-metallic expansion joint" is another category according to its shape, and its structure is completely different. Don't confuse it.
The most painful pain point in model selection: pressure resistance
The biggest weakness of Type A is that it can't bear high pressure. Think about it, no matter how thick the loop belt is, it is still fabric. The metal bellows can withstand the pressure of several MPa. Type A begins to tremble when it exceeds 0.2MPa. Therefore, it is only mixed in low-pressure systems: fan inlet and outlet, dust removal pipeline, desulfurization flue gas pipeline... These places have high temperature and great corrosion, and the metal corrugated expansion joint is prone to fatigue failure. I have done a project in a cement plant. The exhaust gas pipeline at the end of the kiln originally used metal corrugated expansion joints in the cement industry, but it cracked in less than half a year. It was replaced with a type A non-metallic compensator, and there has been no air leak in three years. Why? Because the fabric belt is not afraid of repeated bending due to thermal expansion and contraction, the long-term high-frequency vibration of metal bellows is easy to produce stress concentration. Alas, this matter is to put it bluntly: choose the right place, and Type A is a treasure; Throw it on a high-pressure pipeline, and it is scrap metal.
Type A has minimal and almost negligible thrust on the pipeline. This means that you don't need heavy-duty brackets and guide brackets like metal expansion joints, and the steel money saved is enough to buy several compensators. Isn't it a good deal?
Record of Installation Pit Stepping: The 80% Torque Law
Last year, there was a power plant project, and the Type A non-metallic compensator installed by Party A itself tore apart after less than a month's operation. I went over and looked, boy, the bolts were tight and the bands were bulging. What's the problem? In the cold state, the ring belt is too tight, and as soon as the pipeline heats up and expands, the ring belt has no place to release stress and tears directly.
The ring belt is easy to be compressed and deformed during transportation, so the flatness of the flange surface must be checked first after arrival. When installing, pre-tighten the fixing bolts to 80% torque first, and do not screw them to death. After the hot state of the pipeline is stable, do secondary tightening. If you are constructing in winter, the ambient temperature is low and the ring belt is hard, the preloading force can be smaller, 70% is enough. When the summer is hot, the circle belt becomes soft, and then tighten it again. This thing is not about tightening as much as possible, but about leaving a margin for thermal expansion.
In addition, if there is dust or oil on the flange surface of the ring belt, it must be cleaned up. Otherwise, air will leak during operation and the compression bolt will loosen. Don't ask me how I know, it's all experience gained by tuition.
One sentence summary
Type A non-metallic compensator is the most common round fabric fiber expansion joint. Low pressure, low temperature and low thrust are its labels, and flue gas pipes and dust removal air ducts are its destination. If you only write "Non-metallic Compensator Type A" on your drawing, without additional pressure, temperature and guide tube, directly quote according to the standard parameters of "Non-metallic Expansion Joint (Fabric Fiber Expansion Joint)" on this site. Don't worry, you can't go wrong.