What Are the Ways of Fabric Connection? Complete solution of connection process of fabric fiber expansion joint in industrial pipeline compensation
The "fabric connection" we talk about, in the field of industrial pipelines, most likely refers to the joint treatment between non-metallic expansion joints (fabric fiber expansion joints) and pipelines. This type of equipment is usually used in flue gas, hot air and dust ducts, and relies on flexible bands of multi-layer fiber fabric and rubber composite. The connection method determines the sealing and life of the whole compensation system. If you choose the wrong one, the later maintenance can make people collapse.
Flanged connection: the most versatile, but the details cannot be sloppy
Flange connection is the most common way in the field-welding flanges at both ends of the expansion joint, flanges on the pipeline, gaskets in the middle, and the bolts are tightened. It is convenient to disassemble and assemble, and does not need to move the pipeline during maintenance, and directly loosen the bolts and change the ring belt. But the pit is also here: the flange surface and bolt materials are not selected correctly, and it will rust to death in half a year. For example, the PTFE-lined metal hose matching the desulfurization flue gas baffle door has strong acidic medium in the flue gas. The flange has to be made of 316L stainless steel, and the bolts have to be coated with Dacro. Otherwise, it will be too late to break the bolts when disassembling them. The sealing gasket is also cheap. Graphite composite gasket is used for high-temperature flue gas and PTFE gasket is used for low-pressure and normal temperature, otherwise the leakage rate will double directly.
Welding connection: once and for all, but don't expect to change it later
Welding connection is to weld the metal frame of the expansion joint directly to the pipe, without bolts and gaskets. Advantages? Extremely low leakage rate, suitable for high temperature, high pressure and long-term non-maintenance occasions. For example, the power station industry uses corrugated expansion joints, high-parameter steam pipelines, with a temperature above 500℃ and a pressure of 10MPa. Do you dare to use flanges? The spacer blew off long ago. There are also high-temperature axial expansion joints, and the working conditions are continuously stable, so they don't have to be cared for for ten or eight years after welding. The cost is that you have to cut the pipe during maintenance, welding, flaw detection and heat treatment, and the labor cost is more than 3 times higher than that of flange. Therefore, welding is only suitable for those scenarios where "install it and don't plan to disassemble it".
Clamp/hoop connection: a money-saving tool with low voltage and large diameter
The clamp connection looks simple-apply sealant to the end faces of the two pipes, put a rubber compensator or rubber PTFE compensator on it, and use a hoop on the outside. Quick installation, one person can do it in half an hour. It is especially suitable for smoke and air ducts with low pressure (below 0.1MPa) and large diameter (above DN1000). Cement plant denitrification flue loves to use this trick, saving money and construction period. However, the disadvantages are also obvious: the sealing ring is a consumable part, and the rubber ages quickly. If the ambient temperature exceeds 80℃, it can't bear it, so it has to be replaced every two or three years. If the medium contains particulate dust, it will wear faster. To put it bluntly, the clamp is a combination of "cheap, fast and short-lived".
Adhesive connection: Patching is the technical job
The loop belt of non-metallic expansion joint (fabric fiber expansion joint) itself is multi-layer composite, and the loop belt and the metal frame have been vulcanized or bonded into one body when the manufacturer leaves the factory. The scene is just docking the frame with the pipe flange. But what if the ring belt is partially damaged during maintenance? Can't change the whole thing, can you? The sheet has to be patched on site with a special adhesive. This job looks simple, but it is actually very demanding on curing time and temperature. I met a customer two days ago, saying that it opened the glue after two months of mending. I asked: What is your curing temperature? He said that the workshop was 5℃ in winter, and it was used directly after gluing. That certainly won't work! Cure at room temperature for at least 24 hours, and ensure that the ambient temperature is not lower than 15℃. If it is a high-temperature zone, it is necessary to use heat-resistant epoxy glue, which can withstand the temperature above 150℃ after curing. Tsk, not many people pay attention to this detail.
Three elements of model selection: temperature, pressure and space
Which one do you choose? There is no "best", only "most suitable". Staring at three numbers first —Medium temperature: Basically say goodbye to rubber and ordinary bonding when it exceeds 300℃. Flange bolts should pay attention to high-temperature creep, and welding is more reliable.Pressure rating: Flanges or welding are preferred above 0.1MPa, and clamps below 0.1MPa can also be made up.Installation space: The narrow clamp is easier to use than the flange, such as the double hinge expansion joint of air-cooled island vacuum pipeline, which has a compact space and can't be sealed with a clamp, so it can only be welded.
Cement industry metal corrugated expansion joint, pipeline temperature fluctuation large, dust. Some people tried to save trouble with welding. As a result, two years later, the ring belt wore out and had to be replaced. The pipe had to be cut, and the kiln was shut down for three days, resulting in a loss of millions in output value. If the flange connection was used at the beginning, with the double-sealed single-axis circular baffle door, the sealing grade could reach more than 99.9%, and it would take half a day to change the ring belt. On the other hand, the double hinge expansion joint of air-cooled island vacuum pipeline, welding is the only choice in high vacuum scenario, and the flange leakage rate can't pass the test at all. Once the vacuum degree drops, the power generation efficiency plummets.
Don't be fooled, turn your own standards
To put it bluntly, many people can't even figure out the temperature threshold. If you are not sure, go directly to this site"National Standard for Non-Metallic Expansion Joints"Or compare the article "The Specific Function of Expansion Joint Guide", which is much more realistic than listening to bragging. The way of fabric connection seems simple, but behind it is the comprehensive consideration of material science, thermodynamics and sealing technology. If you choose the right one, the pipeline will run safely for ten years; If you choose wrong, half a year will make you doubt your life.