To be honest, I have been doing pipeline compensation for a long time, and customers often ask, "Where are non-metallic expansion joints generally used?" In fact, behind this problem, they often have suffered from the loss of metal expansion joints-cracking at high temperatures, corrosion and perforation, or can't fit in at all. Today, I will not take a detour, but directly break these main battlefields apart and crumble them into pieces. All of them are actual combat experience.
Power station boiler and flue gas system: the main battlefield of non-metallic expansion joint
How big can the temperature difference be in the air duct, flue and desulfurization tower inlet and outlet of thermal power plant? Cold to hot, the temperature difference of several hundred degrees is common. Moreover, the flue gas carries sulfide and chloride ions, which is extremely corrosive. The metal expansion joint often can't last a maintenance cycle here, and the weld cracks and intergranular corrosion can't be repaired. At this time, non-metallic expansion joints (especially fabric fiber materials) become standard.
The inlet and outlet of desulfurization tower must be matchedDesulfurization flue gas baffle doorUse. Think about it, when the smoke baffle door is switched, it will produce impact and vibration, and the metal expansion joint can't absorb the three-dimensional displacement at all. The result of hard carrying is cracking. The same cannot be said for non-metallic expansion joints, which also isolate vibrations and protect the entire flue system. We distributed a batch to a power plantRectangular non-metallic expansion jointIt is used between the outlet of the induced draft fan and the desulfurization tower, and it has been operated for three years without any problems. Remember, under the working condition of power station, the non-metallic expansion joint should not only consider the thermal displacement, but also the design and sealing structure of the guide tube. Otherwise, the high-temperature flue gas directly washes the fiber layer, and the life of the non-metallic expansion joint is greatly reduced.
Cement Industry: Flexible Responsibility in High Temperature Dust Environment
On the cement production line, from the preheater to the dust collector, the inside of the pipeline is full of high-temperature and high-dust gas, and the temperature is above 350℃ for a long time, occasionally rushing to 500℃. The metal corrugated expansion joint is prone to dust accumulation and stuck here, and once worn out, a new one will have to be stopped for a few days. The advantages of non-metallic expansion joints come out-wear resistance, easy replacement, and adaptation to large angle deflections of pipes.
Many cement factories like to putMetal Corrugated Expansion Joints in Cement IndustryAndNon-metallic expansion joints (fabric fiber expansion joints)Used with: metal bellows is responsible for axial compensation, and non-metal is responsible for lateral and angular displacement, both without delay. When selecting, it should be noted that the dust of cement plant contains silicon and has high hardness. The skin of non-metallic expansion joint must be thickened with wear-resistant layer, and the guide tube should be detachable to facilitate dust cleaning. Before, a customer had a cheap picture and used a general-purpose non-metallic expansion joint. As a result, it was worn out in half a year, which was not worth the loss.
Metallurgy and Steel: "Soft Connection" in High Temperature Flue Gas Pipeline
The working temperature of flue gas pipelines of blast furnaces, converters and heating furnaces often exceeds 500℃, even above 800℃. Metal expansion joints fatigue crack quickly at this temperature for a simple reason-the yield strength of the metal decreases at high temperatures, and the cyclic stress is wasted as soon as it is superimposed. The multilayer structure of non-metallic expansion joint (including thermal insulation layer) can effectively block the heat radiation, and can absorb the lateral and angular displacement caused by thermal expansion of the pipe.
Then exactly how to choose? Depends on the temperature range. When the temperature exceeds 600℃, ordinary silicone cloth skin won't work, so ceramic fiber cloth with multi-layer insulation felt has to be used. We have made a batch for the steel millHigh temperature axial expansion joint, but that was metal; In the position where three-dimensional compensation is needed, non-metallic expansion joints are used. Another point: the pipe diameter of the metallurgical industry is often very large, circular and rectangular. Non-metallic expansion joints can be made into any shape, and it is convenient to install on site, unlike metal expansion joints that have to adjust the flange surface when they correspond.
Chemical Industry and Environmental Protection: Corrosion Resistance is the Last Word
In the desulfurization, denitrification and pickling process sections, the medium contains sulfur, chlorine and acid, and the pH value is often below 1. Even if the metal expansion joint is lined with rubber and PTFE, the matrix will rot immediately as soon as the edge gap leaks. But here comes the problem:PTFE compensatorAndrubber compensatorAlthough they are corrosion resistant, they have limited pressure bearing capacity and are difficult to make into large rectangles structurally. At this time, the advantages of non-metallic expansion joints are reflected-they can be made into rectangular or circular structures, which are suitable for various irregular flues, and the overall cost is low.
"Can I replace the non-metallic expansion joint with a rubber compensator?" I said you depend on the working conditions: rubber is acid and alkali resistant but not high temperature resistant, and it softens when it exceeds 120℃; The PTFE film and silica gel layer in the skin of non-metal expansion joint can be combined, which is both temperature-resistant and corrosion-resistant, and the cost is 30% to 40% cheaper than that of metal expansion joint fully lined with PTFE. If you happen to have a circular flue, you can also considerRound Flap Door (Double Seal)With the use of non-metal expansion joint, the sealing effect is better.
Selection reminder: Don't just look at the material, the working condition details determine the life
AgainNon-metallic expansion joints (fabric fiber expansion joints)Used in power stations and cement plants, the thickness of fiber layer, sealing structure and guide tube design are different. Did you do it according to JB/T 12235-2015 standard? Does the installation location reserve enough access space? In order to save space, many customers install the expansion joint in the corner. As a result, when changing the skin, they can't even reach in the wrench, so they can only cut the pipe. There are really quite a few people who have stepped on these pits.
In addition, don't forget to consider it together with other products. For example, the flue is fittedManual plug-in insulation doorOrElectric plug-in insulation doorConvenient isolation during maintenance; If you need a higher seal grade, you can chooseDouble-sealed single-axis circular baffle doorOrSingle-axis double-flapper door。 The non-metal expansion joint and the baffle door are a perfect match. One is responsible for compensation and one is responsible for cutting off. Only when the two cooperate well can the whole pipeline system run stably.
Your current working conditions, is there high temperature, corrosion, or large displacement? Find the crux, then select the corresponding non-metallic expansion joint, and don't blindly follow the material. For specific models and sizes, you can compare the expansion joint model and size instructions on our website, or consult the technology directly to avoid detours.