1. Thermal expansion and contraction are the natural enemies of pipelines, and the expansion joint is the "pressure reducing valve"
The flue ducts of power plants and chemical plants are hundreds of meters long at every turn, and the medium temperature tosses back and forth from tens of degrees to hundreds of degrees. The linear expansion coefficient of steel pipe is there-about 1.2 mm per 100 degrees of temperature increase per meter. You calculate, a 50-meter flue, with a temperature difference of 300 degrees, has to be stretched by 18 centimeters. Without expansion joints, pipeline connections, brackets and equipment interfaces have to bear this stress, ranging from leakage to cracking. The core function of the flue expansion joint of the air duct is to absorb this axial, lateral and even angular displacement, so that the duct system "has a place to gasp".
The general-purpose corrugated expansion joint and high-temperature axial expansion joint of this station are specialized in this work-through the elastic deformation of the corrugated structure, the thermal stress is digested in itself. To put it bluntly, the expansion joint is to install a "spring cushion" on the pipeline system, which turns the head-on into a soft solution.
2. Sealing is the vital gate of flue system, and non-metallic expansion joints are stronger than metals in this regard
Many people only focus on displacement compensation, but ignore that high-temperature smoke, corrosive gases and even dusty particles run in the flue duct. Once leaked, it not only wastes energy, but also may cause excessive environmental protection and equipment corrosion. The second function of the flue expansion joint of the air duct is sealing. At this time, the non-metallic expansion joint (fabric fiber expansion joint) shows an advantage-its flexible sealing layer can keep the air leakage rate to an extremely low level, and it is temperature-resistant and corrosion-resistant.
The rectangular non-metallic expansion joint of this station is used a lot in the inlet and outlet of desulfurization flue and dust collector, because it has good sealing effect and can absorb multi-directional displacement. On the other hand, although the metal rectangular expansion joint has high strength, the corrugated plate has many welds and is difficult to seal, which has to be compensated by the guide tube and the sealing structure. Tell me, is that the truth?
3. Vibration and noise reduction and pressure isolation: Invisible skills of air duct flue expansion joints
When the blower and induced draft fan were turned on, the whole flue shook. Vibration not only produces noise, but also makes the weld fatigue crack. The corrugated or fabric layer of the expansion joint itself has damping properties, which can buffer mechanical vibrations and fluid pulsations. Another trick: when the flue system needs to be overhauled or switched in sections, it can be used with the flue gas baffle door-such as the desulfurization flue gas baffle door and the electric plug-in insulation door of this station-and the expansion joint can withstand a certain internal pressure difference, making the valve easier to operate.
To put it bluntly, expansion joints are not only "expansion joints", but also "shock pads" and "pressure buffers". Think about it, without this layer of damping, how many starts and stops can those welds hold?
4. Cases of selection rollovers abound-temperature and media determine whether metal or non-metal
Two days ago, I met a customer. The temperature of the preheater flue of the cement plant was 450 degrees. It was supposed to use metal corrugated expansion joints or high-temperature axial expansion joints, but they bought ordinary non-metallic expansion joints cheaper. It burned through in three months. On the other hand, some desulfurization flues have low temperature but strong acid corrosion, so metal expansion joints have to be lined with PTFE, which doubles the cost. It is better to directly apply non-metal expansion joints + corrosion-resistant coating.
Therefore, the key to the role of the air duct flue expansion joint lies in the selection:
- Temperature over 400 degreesMetals are preferred, such as corrugated expansion joints for power station industries and metal corrugated expansion joints for cement industries.
- There is corrosion or large amount of compensation is required: Non-metallic ones (such as rectangular non-metallic expansion joints and rubber compensators) are more reliable.
- Frequent alternation of hot and cold: Also consider pressure balanced types, such as straight tube pressure balanced expansion joints, to eliminate thrust on equipment ports.
Don't buy expansion joints with standard parts thinking. Every working condition is a custom job.
5. These small details of installation and guide tube directly affect the actual effect of expansion joint
The expansion joint is installed backwards, the guide tube is welded crooked, and the tie rod nut is not adjusted properly. No matter how good the product is, it is useless. The guide tube of the flue expansion joint of the air duct has two functions: one is to guide the airflow to pass smoothly and avoid vortex erosion ripples; The second is to protect the corrugated box from the direct impact of high-temperature flue gas. This site has an article dedicated toSpecific Function of Expansion Joint Guide Tube, very thorough.
In addition, when installing the expansion joint of the large tie rod, attention must be paid to the direction arrow pointing to the flow direction of the medium, and the tie rod nut must be pre-adjusted to the designated position when it is cold, otherwise the bellows may be broken when the hot state expands. These details are the most valuable experience in engineering practice. Think about it, if a nut is screwed wrong, tens of thousands of dollars of equipment will be wasted. Is it wrong?
6. Summary: Don't buy the expansion joint as a standard part, it is a system component
The function of air duct flue expansion joint is comprehensive-displacement compensation, sealing, vibration reduction, pressure isolation and equipment protection. However, the working conditions of each project are different, so the formula cannot be set. It is recommended to ask the manufacturer clearly before selecting: medium temperature, pressure, composition, pipeline direction, position of fixed bracket, whether it is installed horizontally or vertically, and how much expansion is.
There are various types of expansion joint products in this station, from non-metallic expansion joints to metallic rectangular expansion joints, as well as special purpose rotary compensators, sleeve type pipe expansion joints. Only by matching to specific working conditions can it play its due role. If you are not sure, it is much more worry-free to call and ask the technician to do the math for you directly than to buy with your eyes closed.