What exactly does a cylindrical non-metallic compensator look like? — — Structural disassembly and material selection
Let's talk about the circle structure first. The biggest difference between cylindrical non-metallic compensator and rectangular non-metallic expansion joint is that the cross section is round, which is specially used in circular pipes-smoke duct, dust removal pipe and desulfurization flue gas pipe. You should think of it when you see circular pipe. The main body consists of four layers: outer skin (silicone cloth, fluororubber cloth, polytetrafluoroethylene cloth, etc.), heat insulation layer (ceramic fiber blanket), inner lining layer (stainless steel wire mesh), plus metal flanges at both ends. The skin material directly determines the bottom limit of temperature resistance and corrosion resistance. For example, the temperature resistance of silicone cloth skin is about 200℃, and the temperature resistance of fluororubber cloth is above 250℃. If it is higher, it will be the scheme of PTFE compensator. The thickness and number of layers of ceramic fiber blanket determine the thermal insulation ability. When the instantaneous high temperature rushes to 800℃ (such as the pipe behind the flue gas baffle door), the thermal insulation layer must be thickened or multi-layer design must be adopted. The lined stainless steel wire mesh is designed to prevent negative pressure from deflating the skin while increasing mechanical strength.
What exactly does it solve? — — Comparing the three core advantages of metal expansion joints
One is to absorb multidimensional displacements. Cylindrical non-metallic compensators can absorb axial, lateral and angular displacements simultaneously, unlike general-purpose corrugated expansion joints that are particularly sensitive to lateral displacements. Excessive lateral displacement of metal bellows is easy to become unstable, while the non-metallic fabric structure is naturally flexible, and the three-dimensional displacement can be easily digested by the folds and fiber deformation of the skin. The second is vibration and noise reduction. The fabric fibers themselves are naturally porous sound-absorbing materials, and pipe vibrations are greatly attenuated as they are transmitted through the skin and insulation. Think about it, vibration and noise have always been a big problem in the export of power plant fans and steel mill dust removal fans. If you replace them with non-metallic compensators, the effect will be immediate. Third, corrosion resistance and wear resistance. Desulfurization flue gas contains acid and dust. In this environment, the surface of metal bellows will be fatigued, cracked and pitted, while non-metallic skin (especially fluororubber or polytetrafluoroethylene) can withstand it more. Two days ago, there was a customer of a cement factory, who originally used a metal corrugated expansion joint in the cement industry. It leaked in less than half a year and was replaced with a non-metallic one. It was still stable after two years. The difference was not slightly.
The easiest pits to step on when selecting a model-pressure, temperature and medium must all be missed
Although non-metallic compensators are corrosion resistant, they must not be used in high-pressure conditions. The industry standard JB/T 12235-2015 reads in black and white: The design pressure generally does not exceed 0.1MPa, that is, about one atmosphere pressure. Low pressure desulfurization flue, negative pressure dust collection pipe is fine, but you want to connect it to the steam pipe? Then wait for it to explode. Be more careful about temperature: Is the medium temperature a sustained value or an instantaneous peak? For example, the instantaneous temperature of the pipe behind the flue gas baffle door may rush to 800℃ during switching operation, so it is necessary to thicken the heat insulation layer or adopt multi-layer non-metallic expansion joints. If the material is selected wrong, the whole set of equipment may be scrapped in a few days.
Media properties are even more deadly. Flue gas containing acid (sulfuric acid, hydrochloric acid) or alkali will corrode ordinary silicone cloth, so the skin made of fluororubber or polytetrafluoroethylene must be selected. Don't think that the name "non-metal" is all-purpose-rubber compensators will expand and fail in oil media, which is exactly the same. One more point: don't just look at the operating temperature, but also the media flow rate. High-speed dusty airflow will polish the skin like sandpaper. At this time, lining stainless steel wire mesh is the life-saving talisman. To put it bluntly, if one of the three parameters of pressure, temperature and medium is missing, selection is a gamble.
Installation and Maintenance: Those Details Nobody Tells You
Be sure to reserve the amount of pre-stretch during installation, especially for high temperature pipes. Both ends of the cylindrical compensator are flanged, and the bolts should be tightened diagonally to prevent skin wrinkles. It can't be tightened casually. Once the skin creases, the local stress will be concentrated, and the life will be cut in half directly. For maintenance, check the skin surface regularly for wear, bulging or hardening. If local damage is found, special repair tape can be used for emergency treatment, but it won't last long, so it is recommended to replace it in the whole circle. In addition, the tie rod nut should never be screwed to death-the function of the expansion joint tie rod is to limit the position, not fix it. Two days ago, a customer called and asked, "Does the screw of the expansion joint need to be disassembled?" Most of this problem is because he didn't understand what the tie rod was used for. The tie rod limits the maximum displacement of the compensator during operation to prevent over-stretching, but the nut must leave room for free movement, otherwise the compensator will "stiffen", and the thermal expansion and contraction of the pipe will all be held back on the flange, which will cause accidents sooner or later.
And the selection logic of similar products: When to choose cylindrical non-metallic? When to choose something else?
Circular pipes, low pressure, high temperature or corrosive media, preference is given to cylindrical non-metallic compensators. If the pipe is square, choose a rectangular non-metallic expansion joint. If the design pressure exceeds 0.1MPa, you have to use metal expansion joints-general-purpose corrugated expansion joints, corrugated expansion joints for power station industry or large-diameter thick-walled expansion joints, all of which can be carried. There is also a special scenario: air-cooled island vacuum pipe, which must use air-cooled island vacuum pipe double-hinged expansion joint, which is metal, and non-metals will deflate under vacuum. The selection is not black or white, it depends on the actual working conditions-temperature, pressure, displacement, medium and installation space, all of which are indispensable. Don't be lazy, list all five parameters before selecting. Even if only one displacement direction is ignored, the compensator will be crippled when installed. In the final analysis, cylindrical non-metallic compensators can fire not because they are universal, but because they use the right materials in the right places.