1. Let's start with "non-metallic expansion joint"-what is an oversized non-metallic compensator?
To put it bluntly, the non-metallic compensator is what we often call the non-metallic expansion joint. The industry standard is calledNon-metallic expansion joints (fabric fiber expansion joints)For details, please refer to JB/T 12235-2015. How do you understand the word "oversized"? Usually refers to compensators with rectangular or circular cross-sections with a diameter of more than 1 meter or even larger. For example, the flue duct and desulfurization tower of thermal power plants are used for inlet and outletRectangular non-metallic expansion jointThe diameter is more than 3 meters ×5 meters at every turn. The main body of this type of product is not a metal bellows, but a combination of high-temperature resistant fabric skin, thermal insulation filling layer and metal frame. Its ability to compensate for displacement does not depend on corrugation deformation, but all depends on the flexibility of the skin and the sliding structure of the frame-to put it bluntly, "soft connection".
2. Compared with the metal compensator, what is the advantage?
Metal expansion joints (e.g.Universal corrugated expansion joint) It is indeed reliable on high-pressure and high-temperature steam pipelines, but when faced with high-temperature flue gas and corrosive media (such as wet flue gas after desulfurization), metal bellows are easily corroded or fatigue cracked. The advantages of super-large non-metallic compensators are precisely:
- Corrosion resistance-The fabric skin material is usually fluororubber, silicone rubber or polytetrafluoroethylene coated cloth, which is easy to deal with SO₂ and acid-base droplets;
- Large compensation displacement-It can absorb axial, transverse and angular displacements simultaneously, and does not produce metal fatigue problems;
- Light structure— — Large-size metal expansion joints are not only expensive, but also scary in weight. Only the frame of non-metal models is metal, and the overall weight can be saved by more than half.
Two days ago, I met a cement factory customer. The high-temperature fan pipeline at the end of the kiln was originally usedMetal rectangular expansion jointAfter less than a year of use, the air leaked. After replacing it with a rectangular non-metallic expansion joint, there was no problem for three years. Do you think it's irritating?
3. How to choose the site? Don't step on these pits.
The most common mistake to make when selecting a model is to only look at the caliber regardless of the medium temperature and pressure. The working temperature of super-large non-metallic compensator is generally limited by the skin. Ordinary silicone cloth can withstand the temperature of 150~200℃, and Teflon cloth can reach about 250℃. If it exceeds 250℃, ceramic fiber insulation layer has to be added. In terms of pressure, it basically does not exceed 0.1MPa, so it is only used on low-pressure pipes. In addition, the installation direction is also particular-many construction teams try to save trouble, lock the tie rod or install the guide tube backwards, and as a result, the compensator can't play a role. Remember:The guide tube is to be directed toward that direction of the medium flowThe tie rod nut must be loosened by a certain stroke after installation, otherwise it will be a dead knot. What about that? It is right to pull the skin with your hand after installation, and you can feel the looseness.
4. Which industries can't live without it?
Super-large non-metallic compensators are needed for the pipes in front and behind the boiler flue duct and the desulfurization flue gas baffle door. Although the temperature of the flue gas after desulfurization is only 50~80℃, the humidity is high and it contains acidic condensate, which will soon rot with a metal compensator. It is usually accompanied hereDesulfurization flue gas baffle doorUse it together. Cement industry: kiln tail preheater, dust collector import and export, high temperature (350℃ +), large dust, rectangular non-metallic expansion joint with wear-resistant lining can carry. The sintering machine and pellet shaft furnace flue gas pipeline in the steel industry are similar scenes. In additionDouble hinge expansion joint for air-cooled island vacuum pipelineThese kinds of special custom structures are used occasionally, but that's another way to play.
5. Routine maintenance-don't wait until you miss it.
The weakness of non-metallic compensators is skin aging. Under normal working conditions, the fabric skin can be used for 3~5 years, but if the environment is bad, it may be changed in 2 years. Usually, the inspection should keep an eye on the skin surface for bulging, cracking or leakage marks. If local damage is found, you can use high-temperature repair tape for temporary emergency, but it is best to replace the whole piece. In addition, the frame bolts must be tightened regularly-pipe vibration will cause the bolts to loosen and then the skin will be torn. By the way: Don't forget to remove the insulation cotton in the old skin when replacing it. The new cotton should be compressed evenly, otherwise the compensation amount will be discounted. Don't ask me how I know, anyone who has suffered a loss knows.