First, find out: What is a non-metallic telescopic compensator? How is it different from metal?
Non-metallic telescopic compensator, also called non-metallic expansion joint and fabric fiber expansion joint in the industry, is mainly composed of flexible non-metallic skin, thermal insulation layer, frame and guide tube. Its core is one word: soft. This "softness" allows it to absorb the displacement of the pipe in three dimensions-especially angular displacement and lateral displacement, while metal corrugated expansion joints (such as general corrugated expansion joints and external pressure single axial expansion joints) are often inadequate in this respect.
For example, the hot air ducts in the cement industry and the smoke ducts in power plants have high temperatures, lots of dust, and the duct paths often turn. At this time, metal bellows are used, and it won't take long for fatigue to crack. But replacing it with a non-metallic telescopic compensator can last a long time. Why? Because metal bellows rely on corrugation deformation to compensate for displacement, repeated bending is easy to produce stress concentration; The non-metallic skin itself is a flexible body, and its displacement is dispersed by the whole surface, so it is naturally more resistant.
Is "weak" a false proposition? Yeah, it was a misunderstanding.
Second, the "softness" of non-metallic compensator is not a weakness, but just its killer
Many people think it is a soft persimmon when they hear "non-metal", which is a big misunderstanding. The skin of non-metallic telescopic compensator is usually made of multi-layer composite materials: fluororubber, silicone rubber, polytetrafluoroethylene, glass fiber cloth and other combinations. Each layer has a clear division of labor-some are responsible for temperature resistance, some are responsible for anti-corrosion, some are responsible for sealing, and some are responsible for pressure. For example, in the desulfurization flue gas system, the flue gas contains acidic condensate, and the metal bellows corrodes in a few months. Switch to rubber PTFE compensator or non-metal expansion joint, and the life span is directly pulled to two or three years. And guess what? After the customer settled this account, he changed it without saying a word.
For example, the tail flue of the power station boiler uses a rectangular non-metallic expansion joint. The rectangular flue has a large diameter, low pressure, and the temperature is always five to six hundred degrees Celsius. The metal bellows can't be made of such a large size at all. Even if it is made hard, the cost is ridiculously high. Non-metallic ones are easy to handle.
3. Only use the right place, and you will never be bad for a lifetime- -Selection guide of non-metallic compensator
Of course, not all pipes are suitable for non-metals. Its advantage range is clear: low pressure (generally 0.1-0.5MPa), large diameter (rectangular flues with a diameter of several meters are common), large temperature difference (instantaneous temperature difference can reach several hundred degrees), and scenarios requiring large displacement compensation. For example, the preheater pipe of cement kiln and the air-cooled island vacuum pipe-you said the temperature of the air-cooled island vacuum pipe is not high, right? However, the requirements of vacuum degree are strict, and the metal hose is afraid of deflating. On the contrary, the non-metallic fabric fiber structure and internal support ring are better. We have a double hinge expansion joint of air-cooled island vacuum pipeline specially for this working condition, and customers have reported that it has been used for three years without any problems.
Operating pressure, medium temperature, displacement amount. Never throw a non-metal into a high-pressure steam pipe-that's suicide. For high pressure steam, you have to use a metal corrugated compensator, such as an external pressure single axial expansion joint or a universal corrugated expansion joint. What tools to do, hard on non-metal, that is to make fun of life.
4. Installation and daily maintenance, don't step on the three pits
The non-metal compensator is very solid, but if it is not installed properly, it will still be scrapped in advance. First pit: Direction of the guide tube. When installing, be sure to make sure that the direction of the arrow of the guide tube is consistent with the flow direction of the medium. If it is reversed, the airflow will directly wash the skin, and it will not take long to wear it out. The second pit: transport and storage. The non-metallic skin cannot be heavily pressed or folded. Once a crease appears, it becomes a stress concentration point, and it will crack from there in the future. Third Pit: Check the outer layer for wear or aging cracks periodically after operation, especially in high temperature areas. Two days ago, I met a customer who said that he had not taken care of it for two years. As a result, the skin was worn out and smoke leaked. How much does it cost to replace a new one? Shutdown losses are the big one. Therefore, it doesn't take a few minutes to take a second look during daily inspections.
5. How to choose from similar products? Non-Metal vs Rubber vs Metal Bellows
Do you choose a non-metallic or rubber compensator? The advantages of rubber are cheap and easy to install, but the temperature resistance generally does not exceed 120℃. The temperature resistance of non-metallic telescopic compensator can reach more than 1000℃ by replacing the skin material (for example, using ceramic fiber composite layer). However, the metal corrugated compensator has high pressure bearing capacity, but the cost is also high, and the installation space requirements are strict. To put it bluntly, there is no universal compensator, only the best fit. If the pipeline is round and the pressure is low and the temperature is high, choose non-metal; If it is high-pressure steam, you have to honestly use a metal expansion device (general corrugated expansion joint or external pressure single axial type).
The pipeline medium contains strong corrosive substances, such as hydrofluoric acid and concentrated sulfuric acid. At this time, metal and ordinary rubber are not good, so PTFE compensator (lined with PTFE) has to be used. Therefore, when it comes to type selection, you can't pat your head, you have to look at the working condition data.
Don't be superstitious about any kind of product. The non-metallic telescopic compensator is not a panacea, but in the areas where it is good, it is the optimal solution.