1. Start with a field failure: the metal compensator stumbled in the flue system
Last summer, there was a big trouble in the desulfurization flue of a steel mill in Hebei. They use a metal corrugated expansion joint (the one in our stationUniversal corrugated expansion joint), only half a year after installation, the weld began to seep water. After removing it, the inside of the bellows is ashed and scaled, and the acid corrosion has bitten the stainless steel into holes. The project manager spat with me: it cost hundreds of thousands to change a set of metal parts, but the result couldn't last a maintenance cycle.
It's all too common in power plants and steel mills. There are SO₂ and HCl hidden in the wet smoke. The temperature is not high but the humidity is high. In this environment, the metal bellows is just like paper. At this timeNon-metallic skin soft connection flue compensatorThe advantages are completely exposed-it is not afraid of acid and alkali, can absorb the displacement in three directions (axial, transverse and angular), and will not cause fatigue cracking due to stress concentration like metal parts.
Since it's so good, why didn't you use it before? The answer is simple-in the past, the technology was not up to standard, the skin material was not temperature-resistant enough, and the air leakage was fast. However, the current silicone cloth, fluorine tape and multi-layer composite structure are no longer the same level as before.
2. What exactly is non-metallic skin soft connection?
To put it bluntly, it's the one in our stationNon-metallic expansion joint (fabric fiber expansion joint)Another name for. Structurally like a thousand-layer cake: the outermost layer is a fabric fiber layer (silicone cloth or fluorine tape), with insulation cotton and stainless steel wire mesh sandwiched in the middle, and the innermost layer is a sealing layer. In this way, layers are stacked, which not only keeps flexibility, but also holds hundreds of degrees of smoke.
Why is it called "skin"? Because it acts like a soft skin, wrapped tightly around the pipe connection. When the pipe expands and contracts thermally, it follows the stretching or compression; Smoke wants to run out? Blocked by the sealing layer. In terms of material selection, silicone rubber is temperature resistant to 200℃-350℃, and fluororubber can carry it to 400℃. If it encounters a high temperature above 1000℃, there is a combination scheme of ceramic fiber + polytetrafluoroethylene.
Although it is soft, the amount of displacement it can withstand is not small. The lateral displacement is tens of millimeters and the angular displacement is several degrees. For metal parts, it can be realized by connecting several bellows in series, but one non-metallic skin can do it.
3. Compared with metal expansion joints, where is it stronger?
Let's talk to the data. Metal expansion joints (e.g.Universal corrugated expansion jointOrExternal pressure single axial type expansion joint) is prone to fatigue under high temperature, especially in the working conditions of frequent start and stop, and cracks often appear at the root of bellows. Moreover, you have to leave the amount of pre-stretching when installing, so if you don't calculate it, you will dry it for nothing. The installation of non-metallic skin soft connection is much simpler-the flange is clamped, the bolt is twisted, there is no need to pre-stretch, and the slack amount of 5%-10% is enough.
Maintenance is worry-free. If the metal parts are broken, they can only be replaced as a whole. Cutting the pipe and welding the flange can't be done in two days. What about non-metallic skin? Once the strips were removed, the old skin was pulled out, and the new one was laid out. It took half a day to finish. What is the difference in cost? For a compensator of the same size, a non-metal skin costs one-third to half the price of a metal piece.
Of course, it's not a panacea either. Weak pressure resistance is a flaw-generally it can only be used in low-pressure flue systems below 0.1MPa. High-pressure situations (such as the main steam pipe of the boiler) still have to rely onHigh temperature axial expansion jointOrStraight pipe pressure balanced expansion joint。 In addition, the fatigue life is not as good as that of high-quality metal parts. After all, the fabric layer is essentially a polymer material, which will age over time.
4. The three easiest pits to step on during selection and installation
The first pit: just look at the medium temperature, not the radiant heat.A while ago, there was a cement factory customer with a nominal flue gas temperature of 300℃. They chose silicone rubber skin, and it bubbled after two months. After investigation, it was found that the radiant heat on the flue wall made the local temperature of the skin soar to 450℃. What to do? When selecting the model, you must add heat insulation layer, or simply use the composite scheme of fluororubber skin + ceramic fiber.
The second pit: pull the skin as tight as a bandage when installing.There is an installation team to save trouble, pull the skin straight before putting on the strip. As a result, as soon as the temperature rises, the skin has no room to stretch and tears directly. Remember: 5%-10% slack must be retained during installation to allow the skin to fit the flange in its natural state.
The third pit: ignore the deflector.High-speed dusty smoke directly washes the inner wall of the skin, and it can be worn out in three months. Guide tube (the specific function can be seen in the FAQ in our stationSpecific Function of Expansion Joint Guide Tube》) Must be installed, made of stainless steel, and the length should cover the skin area. In addition, the opening direction of the guide tube should follow the airflow, so don't install it backwards.
5. Practical application scenarios: desulfurization flue, cement kiln tail, induced draft fan outlet of power station
These three places areNon-metallic skin soft connection flue compensatorThe most typical place to go.
Desulfurization flue:The flue gas after wet desulfurization has a temperature of 60-80℃, but the acid content is extremely high. Metal parts are rusty for two months, and the fluororubber skin can carry three to five years. From our stationDesulfurization flue gas baffle doorOften used in conjunction with non-metallic skin, one is responsible for isolation and one is responsible for compensation.
Cement kiln tail:The temperature is 400-600℃, and the dust concentration is large. Can't carry it with a silicone rubber skin? Then go on the composite skin of multi-layer ceramic fiber + stainless steel wire mesh. If the local temperature exceeds 1000℃, it can even followMetal Corrugated Expansion Joints in Cement IndustryMake a mixing scheme-use metal parts for the high-temperature section and non-metal skin for the low-temperature section, each taking its strengths.
Power station induced draft fan outlet:The space here is narrow, and the shape of the pipe may be a flat rectangle. Metal rectangular expansion joints are heavy and expensive, making them difficult to install. Replace withRectangular non-metallic expansion joint, weighs only half the weight of metal pieces, and can be customized to fit the pipe perfectly. The square "bulge" at the outlet of the induced draft fan that you see is in all likelihood it.
6. How long is the lifespan? How to replace it if it is broken?
Don't believe the manufacturer's "ten years are not bad". The actual life depends on the working conditions: clean hot air systems (such as boiler cold air ducts) can last 5-8 years, and dusty acidic flue gas systems (such as desulfurization inlets) usually have to be replaced in 2-3 years. There are three key factors that affect the life: temperature, dust concentration and acid dew point. The higher the temperature, the coarser the dust and the thicker the acid, the faster the skin aging.
The replacement process is not complicated. Stop the machine for cooling first, remove the pressing strips on both sides of the old skin, and clean up the residue and rust on the flange surface. Pay attention to the orientation when laying a new skin-if there is a guide tube, the installation mark of the skin must be in the same direction as the guide tube. The bolts should be tightened diagonally multiple times, and the torque should not be too large, because the deformation of the pressing bar will leak.
What if it's partially broken? Small holes with a diameter of less than 20mm can be patched-cut a piece with silicone cloth of the same material and apply high-temperature glue to it. However, if the perforation exceeds 20mm, or the damaged area exceeds 30%, it is recommended to replace it as a whole. Don't feel bad about the money. The downtime loss caused by air leakage is even greater.
With the guys in our stationrubber compensatorThe replacement process is similar, but the non-metallic skin is more afraid of mechanical damage. When disassembling, don't use a crowbar to stab directly. In case the fabric layer is scratched, the small hole will expand and expand.