What exactly is a welded rectangular non-metallic compensator? What is the difference between it and regular non-metallic expansion joints?
To put it bluntly, the welded rectangular non-metallic compensator is a compensator specially designed for rectangular duct systems-such as flue ducts and desulfurization systems in power plants. Different from the common round non-metallic expansion joint, the rectangular structure fits the shape of the flue interface more, and the welded connection ensures the reliability of the seal. A while ago, a customer who was doing a desulfurization project asked me why the non-metallic expansion joint he bought leaked within a few months of installation. One check showed that the choice was wrong-he used a flange connection type, and the vibration of a large manhole door collapsed. The welded type is directly welded to the pipe without the risk of loose bolts, suitable for the rectangular pipe environment with high temperature and high pressure.
Structural dismantling: What parts does it consist of and what roles does each assume?
Welded rectangular non-metallic compensator is generally composed of metal frame (four angle steel or channel steel welded up, down, left and right), non-metallic flexible loop belt (multi-layer composite fabric fiber + silicone or fluororubber), insulation layer (aluminum silicate wool or rock wool) and bead bolts. The metal frame is responsible for bearing load, the non-metal ring belt absorbs displacement, and the insulation layer prevents heat leakage to the external structure. There is a key point: the connection between the ring belt and the frame is not a simple overlap, but a labyrinth seal is formed by strips and bolts-if the bolt torque is uneven during installation, this is the hardest hit area for leakage. Refer to this siteRectangular non-metallic expansion jointThe standard practice of products is usually to add an anti-corrosion fluoroplastic film on the inside of the ring belt to cope with sulfur-containing flue gas.
The easiest pits to step on when selecting a model: pressure, temperature and displacement, all of which can't be missed
Many people think that nonmetallic compensators only need to be "the right size", but they tear in less than half a year. There are three core parameters of welded rectangular non-metallic compensator: design pressure (generally no more than 0.1MPa, but the negative pressure section behind the flue gas baffle door must also be considered), working temperature (silicone ring belt can reach 120℃ for a long time, fluororubber can reach 250℃, and ceramic fiber should be used for higher), and displacement (rectangular pipes usually have lateral displacement and angular displacement, and axial displacement is relatively small). I suggest that when selecting a model, be sure to ask the supplier to provide a fatigue life calculation book based on JB/T 12235-2015. Two days ago, there was a case in a cement plant. Because the rectangular non-metallic expansion joint they selected did not consider the lateral displacement, the side of the ring belt was cracked, and the furnace was shut down for 4 days.
Installation & Maintenance: Weld it and everything will be fine? Don't be careless
Although the welding installation has good sealing performance, it requires extremely high welding quality on site. Clean the rectangular pipe port before welding, and prevent splashing and burning the ring belt during welding-many installation teams save trouble, do not cover the protective layer, and the welding slag falls on the ring belt and burns out the hole directly. In addition, the non-metal ring belt cannot be folded or damp during transportation and storage. After installation, it is necessary to adjust the strip bolt to make the force uniform-you can refer to this siteHow to adjust the tie rod nut of expansion jointThe question-and-answer method of. Daily maintenance depends on two places: First, whether there are cracks, bulges or aging and hardening on the surface of the ring belt; Second, the corrosion of metal frame, especially the desulfurization flue gas environment, it is recommended that the frame material be upgraded to 316L or duplex stainless steel.
How to choose between it and metal rectangular expansion joint? Bottom line: It depends on the working conditions
Metal rectangular expansion joint (this site hasMetal rectangular expansion jointProduct) is suitable for high temperature and high pressure, and requires large thrust compensation, but the cost is high and the installation space is large. The advantages of non-metallic welded rectangular compensator are light weight, corrosion resistance and strong ability to absorb multi-directional displacement. The disadvantage is that it cannot withstand excessive pressure and vacuum. Non-metal is the first choice for low-pressure large-section flue such as the outlet of induced draft fan and the inlet of desulfurization tower in power plants. If it is the high-temperature flue gas at the boiler outlet, the temperature exceeds 400℃, then it is necessary to honestly use the metal rectangular expansion joint. At the end of the day, there is no universal compensator, only the right selection.