What exactly is a non-metallic compensator? What is the essential difference with metal corrugated expansion joint?
Non-metallic compensators (also called fabric fiber expansion joints and non-metallic expansion joints in the industry) are not the same thing as our common metal corrugated expansion joints. The core materials of non-metallic compensator are flexible non-metallic materials such as high-temperature-resistant coated fabric, rubber and polytetrafluoroethylene, which are made into a soft joint. The metal corrugated expansion joint absorbs displacement by elastic deformation of stainless steel corrugated pipe. Different ways, application scenarios are naturally different.
For example, the metal corrugated expansion joint is like a tough guy, which can carry high pressure, but it is afraid of corrosion and fatigue. The non-metallic compensator is like a master of jiu-jitsu, which can't bear high pressure, but it is resistant to high temperatures, corrosion, and can absorb large displacements in three dimensions. You're asking tough guys to do jiu-jitsu work, isn't it realistic? The other way around is the same.
Why can it gain a firm foothold in the harsh working conditions of high-temperature flue duct, power plant desulfurization and cement kiln tail?
Resistant, big and good.ResistanceHigh temperature-the ceramic fiber layer can withstand more than 1000℃;ResistanceCorrosion-Polytetrafluoroethylene or acid-resistant rubber layer directly attacks acidic gas;LargeDisplacement-Rectangular non-metallic expansion energy saving absorbs displacement in X, Y and Z directions at the same time, and metal parts can often only absorb axial or transverse directions. In addition, the vibration reduction effect is first-class. If the fan inlet and outlet pipes are installed with it, the vibration can eat more than half.
In the desulfurization flue of power plant, although the flue gas temperature is not high, it is heavy in moisture and contains acidic condensate. It won't take long for the metal corrugated expansion joint to be pitted and perforated. Replace it with a non-metallic expansion joint (such as this station'sRubber PTFE compensatorOrNon-metallic expansion joint (fabric fiber expansion joint)), the inner layer is tetrafluorine acid-resistant, and the outer layer is fiber insulation, which is still intact after three or four years of use. Is that the truth?
The shortcomings are also obvious. Don't treat it as a panacea
Non-metallic compensators are not without drawbacks. The pressure capacity is pitifully low-generally no more than 0.1MPa, that is, just over one atmosphere. If you use it on a steam pipe or high pressure oil pipe, it will explode in minutes. In addition, it is afraid of sharp objects scratching, and it is easy to leak air if the flange surface is uneven during installation. In terms of life, the fiber and rubber layers will age, but according to JB/T 12235-2015 standard, the design life of regular manufacturers can cover the overhaul cycle of the unit (usually 3~5 years).
Two days ago, a cement factory purchaser spat with me, saying that the metal expansion joint in their kiln tail pipeline cracked in less than a year, and it was annoyed to death after several changes. I suggested that he replace it with a rectangular non-metallic expansion joint with a temperature of about 800 ℃ and a composite layer of ceramic fiber + silicone cloth. And guess what? Used it for more than two years without any problems. Therefore, everything is easy to say if the selection is right.
Focus on these four parameters when selecting
- Design temperature: Look at the resistance temperature of the fabric layer. For example, ceramic fiber can reach 1260℃, but the actual use should leave a margin.
- Working pressure: Non-metallic compensators are mostly used in low-pressure smoke ducts, and don't think about them if they exceed 0.1MPa.
- displacement amount: The three directions of X, Y and Z should be calculated clearly. Metal parts can be calculated as transverse axial, and non-metals can be calculated as three-dimensional.
- Media composition: The desulfurization flue gas has a large moisture content and acidity, so acid-resistant PTFE or rubber materials must be selected, such as this station'sRubber PTFE compensator。 If the cement kiln tail contains alkaline dust, then alkali-resistant coating must be used.
The national standard JB/T 12235-2015 has clear test methods for fatigue life and air tightness.
When should you choose a non-metallic compensator?
Low pressure, large displacement, high temperature, corrosive mediaOccasions, preference is given to non-metals. Specific scenarios include: the pipelines in front and behind the desulfurization flue gas baffle door, the inlet and outlet of the fan in the cement industry, the flue of the power station boiler, the air-cooled island vacuum pipeline-and so on. The air-cooled island vacuum pipeline is commonly used thereDouble hinge expansion joint for air-cooled island vacuum pipelineBut that's because the vacuum condition requires a metal seal. As for the Smoke Wind Dao, it is basically a world of non-metals.Flue gas baffle doorOrDesulfurization flue gas baffle doorUsed together, seal and compensate in one step.
Conversely, if high-pressure pipelines (such as main steam), oil media, or occasions where frequent pressure is required, honestly use metal corrugated expansion joints, such as this station'sUniversal corrugated expansion jointOrHigh temperature axial expansion joint。 Don't think about non-metal saving money and hard on it-if you choose the wrong one, it will be more expensive to repair it later than to buy a new one, and the gain will outweigh the loss.
So how about non-metallic compensators? Bottom line: Use it in the right place is an artifact, and use it in the wrong place is scrap metal. Understand your own working condition parameters, and then compare the above points, and basically don't step on pits in the selection.