First break it clear: What is a rectangular outer flanged skin non-metallic compensator?
Don't be fooled by the name, to put it bluntly, it is a variation of the rectangular non-metallic expansion joint-the skin (fabric fiber layer) has been cuffed at the interface. Most people's first reaction is: "Isn't it just adding an edge? Ordinary non-metallic expansion joints can also be used." The difference in structure is actually not small. The core purpose of the outer flanging is to enhance the connection sealing with the pipe flange, while avoiding the skin directly washed by the medium. You go through our stationRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)Page, you will find that the standard type is usually flat or inner flanged, while the outer flanged design is mostly used in scenes with high flue gas dust content and large pressure fluctuation. In the ordinary structure, after the flange is pressed, there is only one layer of contact between the skin edge and the flange surface, and the outer flanging is equivalent to folding the extra part of the skin to form a double or even three-layer sealing surface-this is not a simple edging, but a sealing logic.
What pain points does outer flanging solve?
In the flue behind the desulfurization flue gas baffle door, the medium temperature fluctuates greatly and the humidity content is high. Ordinary rectangular non-metallic expansion joints are used for a long time, and the skin edge is easy to seep water and accumulate dust from the flange gap, which finally leads to leakage. And guess what? The outer flange is equivalent to adding a "skirt" to the skin, which forms a labyrinth seal after being pressed tight. CooperateDouble-sealed single-axis circular baffle doorOrFlue gas baffle doorWhen used, the air leakage rate can be significantly reduced. After some projects are replaced with outer flanged structures, the maintenance period has been extended from half a year to two years. Why is it so much different? Because when the pressure of the ordinary structure fluctuates, the skin edge will rub back and forth with the small displacement of the flange, and the gap will be worn out after a long time; The outer flange disperses the force points to the flange corners, and the wear path becomes longer, which is naturally more durable.
Does it mean that all rectangular flues should be flanged? Neither is it. If your media is clean, the temperature is stable, and the pressure is barely fluctuating, the standard flat-mouth structure is completely sufficient, and there is no need to spend more. The outer flanging consumes more skin materials, and the price will be 15%-20% more expensive by one more hot pressing and shaping process during processing. But then again, this cost is much less than the loss of shutdown at those key nodes where "it has to be shut down for maintenance if it is broken".
Don't just look at the appearance when selecting a type. These four parameters are the core
First, temperature. The upper temperature resistance limit of the skin materials of non-metallic expansion joints (such as silicone cloth and fluorine tape) should be left with a margin of 20%. For example, the design temperature of flue gas is 200℃, so choose a skin with a temperature resistance of 250℃? Stop, the margin is not simply 50℃, but instantaneous overtemperature: the temperature may rush to 280℃ when the desulfurization system starts and stops, and at this time, 20% will become 240℃-you have to calculate according to the highest instantaneous temperature, not the average temperature. refer toNational standard for non-metallic expansion jointsJB/T 12235-2015, material selection must provide a temperature-time profile.
Second, stress. When the compensator with rectangular section is subjected to internal pressure, the inverted edge is the stress concentration area. Especially the position of the flange corner, the tensile stress of the skin and the preloading force of the flange bolt directly determine the sealing effect. If the internal pressure exceeds 0.1MPa, it is recommended to install a limit rod-don't think that it doesn't matter if it is non-metallic. If the pressure is high, the skin will still be bulged into a balloon. How to adjust the tie rod nut? Refer to our site Q&AHow to adjust the tie rod nut of expansion jointNot long-winded here.
Third, displacement. Rectangular compensators typically absorb axial and lateral displacements, but the outer flanged structure will slightly reduce the amount of axial compensation-the flanged fold portion takes up the deformation space. Assuming that the standard model can absorb ±50mm axial displacement, the outer flanged version may only be able to achieve ±45mm. When selecting, if the axial displacement just presses the upper limit, it is recommended to change to a larger gear or change to a double-wave structure.
Fourth, the medium. For flue gas containing acidic gas and particulate matter, the skin should be corrosion-resistant plus wear-resistant layer. Don't listen to people fool the "general type", you have to talk about the working condition data: SO₂ concentration, particle size and flow rate. For example, the dust concentration of the kiln tail flue gas in the cement industry is as high as 100g/Nm³, and the ordinary silica gel cloth will wear out in two months, so it is necessary to use PTFE + ceramic fiber composite skin.
Record of installation pit stepping
Two days ago, I met a customer who installed the flanging direction of the outer flanging compensator backwards-it should have faced downstream of the flue gas, but it turned out to be upstream. Consequences? The high-temperature smoke directly washes the inside of the flange and burns through in three months. Remember two points: First, check the direction of the guide tube before installation (Specific Function of Expansion Joint Guide TubeRefer to the Q&A in our station), the guide tube must point to the flow direction of the medium, so as to ensure that the flue gas contacts the guide tube first instead of directly impacting the skin; Second, leave enough pre-stretching when adjusting the tie rod nut, and don't lock it. The bolts of the rectangular compensator flange should be tightened in diagonal order in stages to prevent wrinkling of the skin. What is the tightening torque? You can refer toMetal hose pressure standardThe recommended value of the bolt torque of the middle flange, generally, the torque of the M16 bolt is between 80-120N·m, and the specific adjustment is according to the flange grade.
If there is a vibration source in the installation environment, such as a fan or reciprocating pump next to it, it is best to add an anti-loosening washer at the flange connection of the outer flange compensator. Don't be too troublesome. We receive several repair cases every year for leaks caused by loose vibration.
Application scenarios are not limited to power stations and cement industries
Cement industryMetal corrugated expansion jointIt is commonly used in kiln heads, but the rectangular flue mostly uses non-metallic expansion joints. Desulfurization flue, air-cooled island vacuum pipeline (such asDouble hinge expansion joint for air-cooled island vacuum pipeline) Rectangular cross-sections are also common. The outer flange is designed inManual plug-in insulation doorOr the inlet and outlet flue of the electric plug-in type insulation door is particularly useful-the vibration caused by the frequent opening and closing of the insulation door is insulated, and the outer flange can buffer to avoid the tearing of the skin root. If you are unsure about the specific selection, directly refer to the parameter table of "Rectangular Non-Metallic Expansion Joint" on our product page.
Don't think that a non-metallic compensator can be bent casually. Although the outer flange structure improves the sealing performance, the overall stiffness is also increased, and it cannot be forcibly twisted or compressed during installation. If the pipeline alignment deviation is found to exceed 5mm at the site, it is recommended to adjust the pipeline support first, and do not expect to rely on the compensator to eat the displacement. If you do that, no matter how good the structure is, you can't handle it.