Let's first talk about how this "Type A" came from
In the circle of non-metallic compensators, Type A is not an official standard model-looking through JB/T 12235-2015 "National Standard for Non-metallic Expansion Joints", you can't find the word "Type A". It is a conventional name in the industry according to the structural form. To put it bluntly, it usually refers to the kind of structure with an integral frame, multi-layer composite skin, and flanged connection.
When you open the product page of "Non-metallic Expansion Joints (Fabric Fiber Expansion Joints)" on this site, you will find that the actual products match Type A-skin, thermal insulation cotton, stainless steel wire mesh and flange. Why is it called Type A? Because when the non-metallic compensator was first made, this simplest and most versatile structure was ranked first, and it became the default option over time. Like A4 paper for typing and typesetting, no one stipulates that it must be called A4, but everyone just calls it.
Dissecting a Sparrow: What Does a Type A Nonmetallic Compensator Really Look Like?
frame(angle steel or channel steel welding),skin(multi-layer composite of silicone cloth + fluorine adhesive cloth + glass fiber cloth),fill layer(aluminum silicate wool or rock wool). Here is a detail that is easy to overlook: the skin is not a layer of cloth, but stacked like a thousand-layer cake. Each layer of material is responsible for different functions-the outer layer is weather-resistant, the middle layer is pressure-bearing, and the inner layer is temperature-resistant. What is the temperature resistance you ask? The conventional A-type can carry about 350℃. If the flue gas temperature is higher, it has to be high-temperature resistant, such as the all-metal scheme of "high-temperature axial expansion joint" of this station.
Let's talk about the framework. A-frame is generally symmetrical on four sides, and can be made in circular or rectangular shapes. However, there is a pit when it is rectangular: the aspect ratio can't be too large, and the stress at the corners is concentrated when it exceeds 2:1, so the skin is easy to tear. We'll talk about this case later.
What is the difference between type A and type B and type C?
To be honest, the definitions of Type B and Type C of different manufacturers may be different. Some call the one with the guide tube type B, and some call the one with the insulation layer type C. But Type A is almost a consensus-the most basic, the cheapest, and the fastest delivery time.
Take a practical case. Two days ago, a cement factory purchaser called, saying that their pipeline went through the kiln tail flue gas, the temperature fluctuated greatly, and there was dust, so they had to have a non-metallic compensator. I asked him you choose type A? He's right. But when I looked at the working conditions, the pipeline section was square, and the aspect ratio exceeded 2:1. When the four-sided symmetric structure of Type A was used, the stress at the corners was concentrated, and the skin would tear before long. Finally, the "rectangular non-metallic expansion joint" is recommended, which is actually a variant of Type A, but the frame shape and corner treatment have been strengthened. So, don't stare at the letters. Whether the structure can adapt to the direction and displacement of your pipe is the key.
If the pipe is round and the temperature is not high, use Type A casually. However, if it is a square section, large displacement, and high temperature, you have to consider rectangular non-metallic expansion joints or metal solutions.
Which industries love to use non-metallic compensator type A?
For desulfurization flue in power industry, kiln head and tail in cement industry, and hot air duct in chemical industry, you can look through the product list of this site-"desulfurization flue gas baffle door" and "metal corrugated expansion joint in cement industry" are all matched. The biggest advantage of Type A is that it absorbs large displacements, especially lateral and angular displacements, which are unmatched by metal compensators.
For example, at the chimney outlet of a power plant, the thermal expansion is several centimeters. With a type A non-metallic compensator, one can handle the axial, transverse and torsional directions. If you are on metal, you have to string several models to achieve it. Moreover, non-metal has good vibration isolation effect and low noise, which is why power plants like it.
There were three pits in the selection and I've seen too many people fall into them
The first one: the temperature margin.The design temperature is 350℃, and you just choose Type A at 350℃. As a result, the flue gas contains sulfur and is corrosive, and the aging rate of the skin doubles. To leave a margin, at least above 50℃. The skin material under corrosive media should be upgraded, for example, fluorine tape should be used instead of silicone tape.
Second: Installation space.Type A generally needs to reserve an installation length of 200-300mm, and the space is not hard enough to plug, which compresses the compensation amount. Some customers only have a gap of 150mm on the site, so they have to install Type A. As a result, it collapses as soon as it is installed. In this case, it is better to replace a "rubber compensator" or a "rubber PTFE compensator", and it is better to use rubber for lateral displacement.
Third: media particles.With hard particles (such as fly ash) in the pipe, wear-resistant lining should be added to the inner layer of the skin, otherwise it will wear out in three months. The "rubber compensator" of this station can actually cover some working conditions, but its wear resistance is not as good as the A-type liner scheme. The cost increases by about 30% after adding liners, but the life can be doubled.
In this aspect of maintenance, Type A has an innate advantage
The skin can be replaced locally. Unlike a metal compensator, one breaks the whole cut. You open it every other year and check it to see if the skin is bulging and cracked, and if the insulation cotton has collapsed. Referring to the service life of the expansion joint mentioned in the question and answer of this site, generally, Type A can be used for 5 to 8 years under normal working conditions, but if the medium temperature fluctuates frequently or there is chemical erosion, it has to be replaced in three years.
When installing, apply a layer of high-temperature sealant to the flange connection, which can last for two years. In addition, if you find that the skin is partially damaged, you don't need to change the whole strip. Find a manufacturer to buy a skin piece of the same specification, and fix it by pressing the strip on the spot. Is it much less hassle than a metal compensator?