1. The skin is the "soft rib" of the expansion joint, and it is also the key to determine the life span
The non-metal expansion joint skin of the flue is, to put it bluntly, the most delicate part of the whole expansion joint. When you go to the scene, the metal frames, flanges and bolts are still hard, but once there is a problem with the skin, the whole set of equipment has to lie down. Two days ago, a power plant customer spat with me, saying that the expansion joint of their factory had changed its skin three times a year, and the maintenance workers were almost scolding. I asked them what the working temperature was and whether the flue gas composition had been measured, but I didn't know what I asked. Where does this work? How long to carry the skin is not determined by patting the head, but depends on the design, material selection, installation and maintenance. To put it bluntly, whatever treatment you give the skin, it will pay you back what life span.
2. Structure of skin: fabric fiber, sealing layer, heat insulation layer, one layer must not be lacking
Many people think that the skin is just a piece of cloth, and it can be used by sewing and mending. Tsk, so wrong. The real flue non-metallic expansion joint skin is a composite structure of at least three layers: the outermost layer is fabric fiber, which is responsible for temperature resistance and tensile resistance; In the middle is a sealing layer, usually fluororubber or silicone, which blocks the smoke; The inner layer is an insulating layer, such as ceramic fiber felt, that prevents heat from being directly conducted to the fabric. These three layers are indispensable. Whichever layer is missing, the lifespan will be directly discounted. I have seen the skin used by a cement factory, the insulation layer cut corners, and as a result, the outer layer burned in two months, and the cost of replacing it is more expensive than buying a good one. You do the math?
3. The three main reasons for skin failure: high temperature, corrosion and fatigue, which is the most fatal?
Let me say, these three are not fuel-efficient lamps, but the most ruthless one is the combination punch of high temperature + corrosion. High temperature alone is easy to handle, just choose materials with high temperature resistance; Corrosion alone is also easy to handle, and fluororubber is used as the sealing layer. However, there are both water vapor, sulfur dioxide and hydrochloric acid in the flue gas. When the temperature is high, the acid corrosion rate doubles. What about fatigue? Mainly, the vibration and expansion of the pipe lead to repeated wrinkles of the skin, and micro-cracks occur over time. But to be honest, as long as the pre-stretch is in place during installation and the guide tube is reasonably designed, fatigue failure is uncommon. On the contrary, those projects that do not select materials according to the national standard (JB/T 12235-2015) will wear their skin in half a year. And guess what? Finally, it was found that the design temperature was only marked at 200℃, and the actual operation often rushed to 280℃. That's not a trick.
4. Choose the right skin material: fluororubber for desulfurization flue gas, silica gel composite for cement kiln tail
When it comes to material selection, we have to talk about specific working conditions. The flue gas of desulfurization system has high humidity and many acidic components. The skin sealing layer must be made of fluororubber, which is corrosion-resistant and aging-resistant, and the temperature is very stable within 150℃. The tail of the cement kiln is different. The temperature is always above 260℃, and there is much dust, so fluororubber can't bear it. You have to use silica gel composite skin and ceramic fiber insulation layer to top it. The rectangular non-metallic expansion joint we matched to a cement factory, the skin is silica gel composite structure, and it is still running after more than two years of use. In addition, the power station industry also pays attention to it-for example, the corrugated expansion joint used in the power station industry, the metal part can withstand high temperature and high pressure, but the skin of the non-metallic expansion joint (fabric fiber expansion joint) next to it has to be selected according to the flue temperature, so don't fool it with the general type for cheap. You get what you pay for, and the money saved on the skin has to be spit out of the maintenance fee in the end.
5. Skin replacement signal: Don't wait for smoke before replacing, these signs are more accurate than the alarm
Many customers waited until there was black smoke at the scene before calling for help. At that time, it was too late to regret. In fact, before the skin is about to be scrapped, it will give you several signals: First, the skin surface is bulging or layered, and it feels loose when pressed with your hand; Second, there is seepage or crystal on the edge of the flange, indicating that the sealing layer has been broken; Third, the expansion joint runs with a strange hissing sound, which is the movement of smoke leaking out of the crack. Another trick is simpler: regularly scan the surface temperature of the skin with an infrared thermometer. If the local temperature rises abnormally, it means that the insulation layer may collapse. Don't wait for the alarm to go off. The alarm is generally used to detect smoke leakage. When it goes off, the whole workshop will smell. Inspect once a month, see, touch, listen and measure, which is more reliable than anything else. We matched the flue gas baffle door and metal hose for a chemical enterprise. Because the skin was maintained in time, the whole system was not overhauled for five years.
6. Practical application of non-metallic expansion joint in power station, cement and desulfurization
With all the theory, let's get something practical. The non-metallic expansion joints (fabric fiber expansion joints) made in our station are mainly used in the power station industry with corrugated expansion joints used in the power station industry, and are installed at the inlet and outlet of the flue to absorb thermal displacement and vibration. It is more common in the cement industry. Rectangular non-metallic expansion joints are used in the kiln tail flue and dust collector import and export, and the skin is customized according to the working conditions of the cement kiln tail. For desulfurization system, we also provide desulfurization flue gas baffle door and circular baffle door (double seal), and the non-metallic expansion joint of fluorine rubber is made of skin material, so that the corrosion resistance is full. There are also rubber compensators and rubber PTFE compensators, which are suitable for low pressure and small displacement occasions and have high cost performance. For each project, we will make a specific scheme according to the actual temperature, pressure and media composition, so as to ensure that the skin life can reach the design requirements of 2~3 years or even longer. If you have specific working conditions at hand, you might as well send the parameters, and we will help you calculate how long the skin can last.