Find out first: What exactly is the skin non-metallic compensator?
Look at the name-skin non-metal compensator. Do you feel tall and confused when you hear it? In fact, to put it bluntly, it is the soft connector responsible for "flexible compensation" in the pipeline system. Structurally simple: a circle of metal flanges or carbon steel frames with a special flexible skin sandwiched between them, that's it. And metal expansion joints (like the one in our stationUniversal corrugated expansion joint、Metal rectangular expansion joint), the difference is bigger-those metals deformed by bellows, with high rigidity and small displacement, which are suitable for high-pressure clean media; The skin relies on the elastic deformation of fabric and rubber layer, which can compensate for large displacement in three dimensions and hardly transmit thrust. If you want to draw a picture, the left side is a rigid bellows, and the right side is a soft skin laminated structure. You will understand its "soft" truth at once.
Cough, in practical applications, flue gas pipelines, desulfurization systems, air ducts and other places have high temperature, strong corrosion, alternating hot and cold, and dust particles-do you let metal bellows carry it? It can't handle it for a few days before it cracks from fatigue. At this time, you have to rely on non-metallic compensators to play. So don't be fooled by the name, it's a flexible joint specialized in "dirty work".
Why can it withstand high temperatures and corrosion resistance? — — The mystery of the core material "skin"
The skin is not a piece of cloth, it is a composite of layers of materials. The most common is: the outermost layer is silicone cloth or fluororubber coated cloth, with glass fiber cloth and polytetrafluoroethylene film sandwiched in the middle, and a layer of acid-resistant rubber may be added to the inner layer. Each layer performs its duty-silicone cloth carries temperatures above 200℃, fluororubber is resistant to acid and alkali corrosion, glass fiber provides tensile strength, and polytetrafluoroethylene is anti-adhesion. Let's put it this way, the acid-alkali condensate and high-temperature steam in the flue gas pipeline have long been rusty through the single-layer metal plate, but the skin is forcefully supported by these laminated combinations.
Talk about the desulfurization system. Although the flue gas temperature after wet desulfurization drops to about 50℃, it contains a large number of sulfuric acid and sulfurous acid droplets. The fluororubber layer in the skin non-metallic compensator can directly resist acid-alkali corrosion, and the skin itself does not conduct heat, which can also reduce the heat bridge effect of pipelines. That's why our stationNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion jointThe appearance rate in desulfurization projects of power plants and cement plants is so high. Is that the truth?
Don't step on pits in model selection: how much displacement with how thick skin?
You really can't slap your head when it comes to selection. Two days ago, I encountered the purchase of a cement factory, and I chose a thin skin for the air duct cheaply. As a result, it bulged and leaked in less than half a year-losing dozens of tons of cement output. There are three core principles: compensation amount, pressure level and medium temperature. Take the one from our stationRectangular non-metallic expansion jointFor those with large angular displacement, the skin has to be reinforced, and the number of glass fiber layers is increased from two layers to four layers; If the amount of axial stretching is large, the depth of the preset folds of the skin must be sufficient. The pressure level-low-pressure air duct (below 0.1MPa) can be reinforced with a single layer of skin, but if it is a positive pressure environment above 0.2MPa at the inlet of desulfurization tower, it is necessary to choose a double layer of skin and stainless steel wire mesh to reinforce it.
Medium temperature is a ruthless character. A silicone cloth-glass fiber combination is sufficient below 150°C; If it exceeds 300℃, you have to change the configuration of fluororubber-ceramic fiber. Real case: The raw material grinding ventilation pipe of a cement plant, the temperature is 280℃, the silica gel cloth skin is selected, and it will be layered in half a year. Later, it was replaced with fluororubber skin, and it is still in use for three years now. The wrong layer of material is selected, and the life difference is more than five times.
Install that little thing: to make it work, you have to untie it first
When installing a skin non-metallic compensator, the most taboo thing is "thinking that you can install it when you bring it". Remember three points, one less, and half the equipment will be scrapped.
- Transport tie rod must be removed: In order to fix the skin when the manufacturer delivers the goods, several temporary tie rods will be installed. Connect the pipe directly without dismantling it? Hey, the compensator can't move at all, the thermal expansion is all stuck in the pipes, and the equipment quickly deforms. After installation, confirm that the flange bolts are tightened, and immediately remove the tie rod.
- Pre-stretched (or pre-compressed): According to the design drawings, give the skin an initial displacement amount during installation. For example, if the pipeline is installed at ambient temperature, it will expand when the operating temperature rises, so the skin should be pre-compressed a little during installation, so that the compensation amount is enough. This value is given by the design engineer, so don't guess for yourself.
- Flange centering: The flanges on both sides of the compensator must be aligned parallel with a deviation of no more than 2mm. If forcibly straightened with bolts, the skin will be unevenly stressed, the angular deformation will exceed the limit, and the life will be directly cut in half. Besides, we have to talk to the people in our stationFlue gas baffle door、Round flapper doorIn case of cooperation, pay attention to the compensator to be installed downstream of the baffle door (according to the flow direction of the medium), so that in case of skin leakage, it will not directly rush to the sealing surface of the baffle door.
Once the installation is done, check again-is the tie rod removed? Is the flange bolt torque uniform? Is the pre-stretch amount in place? If this step is done wrong, the compensator will basically hang up. Tsk, we have seen too many cases of equipment being scrapped on site because we forgot to remove the tie rod.
How long is the lifespan? How to fix it if it is broken?
Under normal operating conditions, the design life of the skin non-metallic compensator is 3 to 5 years. But the actual life span is related to the conditions you serve-the medium contains acid and alkali, frequent start and stop, and large temperature fluctuations, so the life span will be shortened to one and a half years; If it is used to clean air ducts, it may be seven or eight years. How do you tell if it's time to change it? Two tricks on-site inspection: first, see if there is any bulging, delamination and cracking on the skin surface; Second, see if the flange bolt is loose (loose means that the skin creeps and deforms). As long as you find bulging or layering, change it quickly and don't delay it.
The first step is to loosen the flange bolt and remove the old broken skin (take care to protect the flange sealing surface). Step 2, clean the flange surface and apply temperature-resistant sealant (silicone rubber or fluorine rubber glue). The third step is to put on the new skin, pay attention to the direction not to install the reverse, and use the diagonal tightening method when tightening the bolts, and the torque is uniform. The whole process is done in half a day, and you don't have to stop production for too long. If there are multiple compensators in the pipeline system, it is recommended to replace them all at once, so as to avoid problems one by one in the future.
From our stationrubber compensatorAndRubber PTFE compensatorIt also belongs to the non-metallic category, but the structure is slightly different-the rubber compensator focuses on vibration damping, and the skin compensator focuses more on high temperature and corrosion. Which one to choose? It depends on the working conditions.