What exactly is a fluororubber non-metallic compensator? — — From the rubber compound to the skeleton, take a look
This thing isn't just any rubber compensator. The non-metallic expansion joint (that is, fabric fiber expansion joint), which we often call, is mainly composed of flexible composite materials, while the high-temperature resistant fluororubber non-metallic compensator replaces the core sealing layer with fluororubber-a special elastomer with full temperature resistance and corrosion resistance.
The outermost layer is silicone rubber glass fiber cloth (fireproof and heat insulation), with stainless steel wire mesh or steel wire ring skeleton sandwiched in the middle (pressure-bearing and deformation-resistant), and the inner layer directly contacts the medium, which is the fluororubber layer. There are fluorine atoms in the molecular chain of fluororubber, and the bond energy of carbon-fluorine bond is frighteningly high, so it can work at 260℃ for a long time, and carry it to 300℃ or even higher in a short time. Plain rubber? Nitrile rubber is soft at 120℃, neoprene is dead at 150℃, and directly carbonized at 200℃.
For this skeleton, some people want to use carbon steel mesh cheaply, but there are usually sulfide and water vapor in the flue gas pipeline, which corrode quickly. The serious thing to do is use 304 or 316 stainless steel wire mesh, or simply use a monolithic metal frame. The non-metallic expansion joints (fabric fiber expansion joints) on our station are usually equipped with Q235 flanges, but stainless steel flanges are recommended for fluororubber compensators-don't save this money, it will be more expensive to replace it with air leakage in the later period.
Comparison of High Temperature Resistance: Viton Rubber vs Ordinary Rubber vs PTFE, Who Is Better for You?
- Common rubber compensator(This site has rubber compensator products): Temperature resistance range-20℃ ~ +120℃, cheap, suitable for water and low-pressure air pipelines. Above 150℃, the life is calculated on a monthly basis.
- PTFE compensator(This site has PTFE compensator): Temperature resistance-60℃ ~ +250℃, excellent chemical stability, almost any acid and alkali are not afraid. However, PTFE is a rigid material with no elasticity. It compensates for displacement by mechanical deformation of corrugated shape, so its fatigue life is limited, and it is easy to creep.
- High temperature resistant fluororubber non-metallic compensator: Temperature resistance-20℃ ~ +260℃ (300℃ for a short time), while maintaining elasticity, can absorb three-way displacement (axial, transverse and angular). Moreover, fluororubber has good tolerance to acidic flue gas and sulfur-containing gases-this is incomparable to PTFE? Wrong, PTFE has stronger chemical resistance, but PTFE compensator (PTFE compensator of this station) has high cost, strict installation requirements, and can't absorb large displacements. The fluororubber non-metallic compensator is better in comprehensive performance: sufficient temperature resistance, good elasticity and moderate price.
Pipeline temperature
Which operating conditions must be fluororubbed? — — Real cases of flue gas, chemical industry and power stations
Two days ago, I met a customer. A section of pipeline was connected behind the desulfurization flue gas baffle door of their factory (there are desulfurization flue gas baffle door products in this station), and the temperature was high and low, with the highest temperature reaching 280℃. The ordinary non-metallic expansion joint used before leaked in half a year. After changing the fluororubber compensator, there was no problem for two years. Why? Because the flue gas contains SO₂ and HCl, which form sulfurous acid after condensation, ordinary rubber is directly corroded, and the chemical inertness of fluororubber makes these acidic gases unable to do anything about it.
Let's talk about the power station industry. Corrugated expansion joints for power station industry (this station has corrugated expansion joints for power station industry) are the norm, but when it comes to boiler outlet and hot air duct, although metal expansion joints are resistant to high temperatures, they can't absorb multi-dimensional displacement and have limited fatigue life. That's when non-metallic compensators come in handy. With fluororubber as the inner lining, the outside is sealed with silicone cloth + glass fiber, and the inside is filled with ceramic fiber. The whole structure is both temperature resistant and flexible. The high-temperature resistant fluororubber non-metallic compensator provided by us for a thermal power plant is applied to the outlet flue of induced draft fan. The flue gas temperature is 280℃, and it has been operated for three years without aging and cracking.
Not to mention the chemical industry. Many high-temperature steam pipelines and heat medium pipelines require compensators to withstand both temperature and pressure. However, note that fluororubber is intolerant to ketone and ester solvents. If the medium is this kind of organic solvent, you have to use PTFE compensator instead (this site has PTFE-lined metal hose and PTFE compensator). Therefore, be sure to find out the media composition before selecting.
I have stepped through the three pits that are most prone to rollover when selecting a model
Pit 1: Just look at the temperature, not the pressure.The bearing capacity of non-metallic compensator mainly depends on the skeleton layer and flange connection. Many supply trademarks claim temperature resistance of 300℃, but the working pressure is only 0.1MPa. If your pipeline pressure is above 0.5MPa, you must thicken the stainless steel wire mesh layer, or choose the reinforced type with metal frame. The rubber compensator and non-metallic expansion joint on our station have clear pressure levels. When selecting the type, compare the working condition table and don't exceed the limit.
Pit 2: Ignore the guide tube.What is the specific function of the expansion joint guide tube? I'll say the conclusion directly: prevent high-speed airflow from directly washing the inner wall of the compensator while reducing the flow resistance. If the flue gas pipe is at a high flow rate (> 10m/s), without the guide tube, the fluororubber layer will be worn out in a few months. Therefore, the manufacturer must be required to equip the guide tube. The material is recommended to be 304 stainless steel, and the thickness is not less than 2mm.
Pit 3: The installation length is hard.Some on-site pipeline installation errors are large, and workers force-pull or press the compensator to install it. The tie rod or screw of the expansion joint (how to adjust the tie rod nut of the expansion joint was talked about in the FAQ of this site) is used to adjust the pre-displacement, not for you to force the counterpart. The installation length must be within the allowable range given by the manufacturer, otherwise the compensator will have internal stress before it works, and the life will be directly reduced by half.
Installation and maintenance: Don't let the last bolt destroy the entire compensator
Check whether the flange surface is flat and the sealing gasket is aligned before installation. When tightening the bolts, tighten them multiple times in diagonal order, and do not beat the torque at once. The most outrageous thing we have ever encountered: the customer tightened all the bolts with an air cannon, and as a result, the flange deformed, the sealing surface warped, and gas leaked directly from the gap. The flange of a non-metallic compensator is usually thinner than that of a metallic compensator, and it will be scrapped if the torque is too large.
In terms of maintenance, regularly observe the external surface for bulging and cracking. When fluororubber is aged, it will harden and crack. Once you find it, don't delay it and change it quickly. Also note: If the plumbing system has a water hammer or violent vibration, the compensator is prone to tearing. In this case, it is recommended to add brackets or limiting devices in front and rear of the compensator. Although the metal parts such as the high-temperature axial expansion joint and the double hinge transverse expansion joint on our station are not used here, the principle is the same-guide the impact force to the fixed bracket.
Don't think about overdue service. The design life of fluororubber non-metallic compensator is usually 5-8 years. The actual use is affected by temperature fluctuations and corrosive media, and it may need to be inspected and replaced in 3 years. Replace when you need to, so as to save pipeline explosion or shutdown for maintenance and greater losses.