Crane pipe non-metallic compensator: pipe "soft joint" that moves as soon as it is twisted
Friends who are engaged in chemical industry and oil depot are familiar with crane pipe-the rotating arm for loading and unloading liquids should be flexible and sealed. But have you settled the bill? The thermal expansion and contraction of the pipeline is several millimeters at a time, and the equipment vibrates hundreds of times a day. Coupled with the visible error during installation, who covers the bottom? The answer lies in the humble "cushion" in the middle of the crane pipe-the compensator. Today, we will talk about the non-metallic compensator used on the crane tube, also called the non-metallic expansion joint (fabric fiber expansion joint). What exactly does it rely on to absorb displacement? How is it different from metal bellows and metal hoses? Don't worry, let's peel it off layer by layer.
Structural dismantling: three layers of "armor" perform their duties
Disassemble a crane tube non-metallic compensator, and you will find that it actually has three parts:
Level 1It is a flexible non-metallic body-multi-layer fabric fiber composite material, and the common silicone cloth, fluororubber and glass fiber cloth are laminated layer by layer. This thing looks soft, but it can withstand high temperatures above 1000℃ (different materials have different upper limits), and it can also withstand acid-alkali corrosion.
Second floorIt is a metal flange or connector that is responsible for the hard connection to the pipe.
Level 3It is an insulation layer, and it is only applied in high temperature conditions.
You may mutter: This soft thing, won't it blow up once the pipe is pressurized? Hey, it just doesn't bear pressure on its own strength. The tension of multi-layer fibers and the coating seal, the principle is the same as that of tire cord cloth-the fibers bear the tension, and the coating ensures airtightness. The greater the pressure, the tighter the fiber pulls, and the stronger the seal.
Working Principle: Four Words-Flexible Deformation
When the crane pipe is elongated or shortened due to temperature change, or the equipment vibration brings lateral offset and angular displacement, the non-metallic compensator "eats" these displacements by bending, twisting and stretching of the fabric fiber layer. Note that it is completely different from the metal bellows-the metal bellows deforms by the elasticity of the corrugations, and each deformation consumes the fatigue life, and it hangs after tens of thousands of uses. The fiber layer of the non-metal compensator has almost no fatigue problem. Why? Because its deformation depends on the relative sliding between fibers and the buckling of the fabric itself, it belongs to "geometric deformation", not the elastic deformation of the material itself. Therefore, it can absorb a much larger amount of displacement, and it can be done in the axial, lateral and angular directions together, one top three.
Sealing mechanism: the greater the pressure, the less leakage
Going further, the sealing mechanism of this thing is kind of interesting. An airtight layer (fluorine rubber or PTFE film) on the inside and a reinforcing layer on the outside. During operation, the medium pressure presses the airtight layer tightly against the fiber layer-the greater the pressure, the tighter the seal. This is the "self-tightening seal", which is exactly the same as the pressure cooker gasket. So it can be used in negative pressure systems (such as flue gas pipes) and corrosive media (acid, alkali, salt spray). By the way, the rubber compensator and rubber PTFE compensator of this station are similar in principle, except that the crane tube non-metallic compensator requires higher flexibility for displacement compensation-after all, the crane tube turns there every day.
Installation and Maintenance: Absurdly High Tolerance
Tell me a practical case. Last year, a chemical plant changed the crane tube compensator. The metal universal corrugated expansion joint was twisted for two hours without aligning its eyes, and finally it was replaced with a non-metal one. Why? The metal compensator requires high installation accuracy, and it will get stuck or leak if it is misaligned by one millimeter. Instead of a metal compensator? Even if the pipe is not aligned, it can "fix" it itself-flexible. Replacement is also convenient: loose flange bolts, old parts are removed, new parts are replaced, no hot welding. Of course, it also has shortcomings: the withstand pressure generally does not exceed 2.5MPa, which is mainly used in low-pressure pipelines; Moreover, fabric fibers are afraid of sharp objects scratching, so transportation and installation should be careful. But then again, the pressure of crane pipe working conditions is usually not high, which is enough.
Selection misunderstanding: Don't think of it as an ordinary canvas soft connection
Two days ago, I met a customer, and when I opened my mouth, I wanted to "canvas soft connection". Isn't it the same thing to say that compensator? Big mistake. The crane pipe has special working conditions: it rotates frequently, may contact flammable and explosive media, and sometimes has to withstand a low temperature of-40℃. When selecting the model, it is necessary to check the medium temperature, pressure, displacement (axial, transverse and angular specific values), and chemical corrosion resistance. For example, rectangular non-metallic expansion joints in this station are often used in flue gas pipes, while round non-metallic expansion joints are more commonly used in crane pipes. In terms of material, fluororubber coating can carry most organic solvents, and silicone cloth is suitable for high temperatures. If you are not sure, directly refer to the national standard of non-metallic expansion joints JB/T 12235-2015, and the parameters are matched one by one.
Say at the end
Non-metallic compensators are nothing new, but in the subdivision scene of crane tubes, its flexibility, sealing and installation width are indeed much more worry-free than metal schemes. The next time you see the "cloth tube" in the middle of the crane tube, don't think it's just a rag-it's a stress relief expert made of fabric and coating.