First understand the "temper" of sintering flue-temperature, pressure, displacement, medium, none of which can leak
The expansion energy saving you choose can't hold up, 90% depends on your understanding of the working conditions. To put it bluntly, the sintering flue is a high-temperature, high-dust and corrosive "thorn head". Don't come up and ask the manufacturer "Is there an expansion joint for DN200?"-first find out the four core parameters.
Temperature:The flue temperature of the sintering machine fluctuates greatly, the nose may be 300℃, and the tail may rush to 800℃ or even higher. To distinguish between sustained temperatures and instantaneous peaks. Metal expansion joints (e.g.High temperature axial expansion joint) can generally withstand to about 600℃, non-metallic (Non-metallic expansion joint (fabric fiber expansion joint)) The upper limit of temperature resistance is usually 400℃, but the instantaneous high temperature can be withstood by multi-layer insulation. When you report to the manufacturer, don't say "about four or five hundred degrees", but give the specific curve directly.
Pressure:The sintering flue is mostly under negative pressure (-5kPa to-20kPa), but there are also positive pressure sections. Don't underestimate the negative pressure. If the type is not selected correctly, the expansion joint will be deflated. The pressure parameters determine the wall thickness and the number of layers of the bellows. If it is negative pressure, pay special attention to the reinforcement ring or liner cylinder.
Displacement:Flue thermal expansion is not in a single direction. Axial elongation, lateral offset, angular displacement-you have to draw the pipe path and mark the position of the fixed brackets and guide brackets. For example, a 30-meter-long flue rises from normal temperature to 400°C, and the axial expansion amount is almost 200mm. MostlyUniversal corrugated expansion jointIt can only absorb axial displacement, and if the flue turns too much, it has to be consideredCompound hinge transverse expansion jointOrCurved tube pressure balance expansion joint。
Media:Sintering flue gas contains sulfur, dust, and sometimes acidic liquid produced by condensation. Metal materials should be corrosion-resistant (such as 316L and 254SMO), and non-metallic skin should be acid-and alkali-resistant. In addition, the dust particles will flush the bellows, at which timeSpecific Function of Expansion Joint Guide TubeIt is reflected-the guide tube can direct the high-speed airflow to the center, avoiding direct impact on the ripples.
Sort these parameters into a table and go through it yourself before sending it to the manufacturer. And guess what? Eighty percent of all selection mistakes are in "I thought".
Metal vs Non-Metal? Don't be in a hurry to pat your head, look at the flue layout and installation space first
Metal expansion joints and non-metallic expansion joints are not substitute relationships, but each has its own household skills. How to choose? Look at three points: installation space, flue section shape and convenience of maintenance.
Flue layout:If the flue is a round pipe with a straight pipe and large space, preference is given to metal corrugated expansion joints (such asCorrugated expansion joint for power station industryOrMetal Corrugated Expansion Joints in Cement Industry）。 Metals have strong pressure bearing capacity and long life, but can only absorb axial or a small amount of lateral displacement. If the flue is rectangular (sintering plants often use rectangular flues), then you can only useRectangular non-metallic expansion jointOrMetal rectangular expansion joint。 The advantages of non-metal are strong absorption capacity for lateral displacement, and light weight and easy installation.
Installation space:Non-metallic expansion joints (also calledNon-metallic compensator) Compact structure, short occupancy length, suitable for space-constrained occasions. However, its maintenance cycle is short, and the skin (fabric fiber layer) generally needs to be replaced in 2-3 years. Metal expansion joints, although longer, are less frequently maintained. You ask: "We only have parking once a year for overhaul, which one to choose?" – and the answer is most likely metal.
Also:If the flue gas temperature exceeds 400℃ and the temperature continues to be high, the non-metallic skin can't bear it, so it can only be made of metal. But metal expansion joints also have shortcomings-such asCorrect installation method of expansion joint of large tie rodAs emphasized in, the large tie rod structure can absorb lateral displacement, but it takes up space, so you have to put it down on the spot. Two days ago, I met a customer who insisted on buying non-metallic ones. As a result, the flue temperature was measured at 780℃, and it only took three months for the skin to burn through. Tsk, sorry for his money.
How to determine the key dimensions and parameters? The path is just the introduction, and this data is the vital gate
Don't think you're done by giving nominal diameter DN. Ten times more important than the path are the following four data:
- Bellows wavenumber:The greater the wave number, the greater the axial displacement that can be absorbed, but the pressure resistance will decrease. You need to inverse the wave number from the calculated displacement and check the fatigue life at the same time.
- Number of layers:When high pressure or corrosive, use multi-layer (double or triple layer) bellows. Such asLarge diameter thick wall expansion jointThe wall thickness is made thick, but the multilayer structure is more resistant to fatigue than the single layer.
- Dimensions of guide tube:The inner diameter and length of the guide tube directly affect the fluid flushing. Too short does not protect, too long increases resistance. refer toSpecific Function of Expansion Joint Guide TubeIn that article, the deflector also plays a thermal insulation role, which can reduce the temperature of the outer wall of the bellows.
- Connection method:Flanged or welded? The sintering flue is mostly welded, but if it is a position with frequent maintenance, it is recommended to use flanges. The number of bolt holes and sealing surface of the flange must match the pipe.
There is another one that is easy to miss —Do you need to remove the screw of the expansion joint？ The nuts on the tie rods are factory locked for transport and installation positioning. Once the installation is complete, the nut must be loosened according to the instructions (leaving a small amount of pre-tightening), otherwise the expansion joint will not work. How to adjust? lookHow to adjust the tie rod nut of expansion jointThat answer has a detailed answer.
When installing, stepping on one of these three minefields will cost money in vain, especially the pull rod and the guide tube
Minefield 1: The transport limit device was not dismantled.Many manufacturers will weld temporary supports or lock tie rod bolts at both ends of the expansion joint. Some installation teams plan to save trouble and weld the supports directly to the pipeline. As a result, as soon as the temperature rises, the expansion joint can't move, and the bellows is forcibly cracked. Remember: The temporary fixtures must be removed after installation and the tie rod nut must be adjusted to the working position.
Minefield 2: Install the deflector in reverse direction.The guide tube is marked with an arrow (ref.The direction of the arrow of the expansion joint refers to), the arrow must point to the direction of the media flow. If installed backwards, the guide can become a throttle, increasing resistance, and dust can build up at the bellows root. Note: There is a gap between the deflector and the bellows to allow a small amount of media to pass through to balance the pressure, but this gap cannot be changed indiscriminately.
Minefield 3: Cold tightening or pre-stretching are ignored.If the flue is installed at room temperature but operates at a high temperature, the pipe will extend substantially. The correct thing to do is to leave the expansion joint in a pre-tensioned state (cold tight) during installation so that the bellows can return to the neutral position in the working state. The specific stretching amount is calculated according to the displacement, and the general manufacturer will provide data. Don't understand? Ask the manufacturer directly for the installation instructions, don't pat your head yourself.
Don't expect "once and for all" for daily maintenance, teach you two tricks to warn leakage in advance
No matter how good an expansion joint is, it is not a perpetual motion machine. Metallic ones get fatigued and non-metallic ones age. But you don't have to lie there and check every day. Two tricks are enough:
First move: Listen to the sound.During inspection, use a listening stick or ear near the expansion joint. If you hear a "fizz" sound, it means there may be a leak. The leakage of metal bellows is usually micro-crack, while the non-metallic ones are damaged. Don't wait until you hear an obvious noise before you make a move. By then, the leak will already be large.
Trick 2: Look at the color and scaling.If yellow-brown or blue oxide scale appears on the surface of metal expansion joint, it means that the temperature exceeds the limit; If there are oil or water stains, it may be a leaking flange sealing surface. If the skin surface of non-metallic expansion joint is bulging and layered, it should be replaced. In addition, pay attention to whether there is any abnormal dust accumulation at the outlet of the guide tube-increased dust accumulation means that the guide tube may fall off or wear.
Every time you stop for overhaul, reach in with an endoscope to see inside the bellows. A lot of small cracks start from the inner wall. Don't wait until it leaks to regret it-replacing an expansion joint is enough money for several endoscopes.
The last step: What do you say when communicating with the manufacturer to not be fooled? Inventory of requirements template attached
Are you ready to call the manufacturer? Don't worry, fill out the list below and read it. As soon as the manufacturer hears it, he knows that he is an expert, and he dares not fool you casually.
List of requirements (according to this you won't be pitted):
- Flue Type: Round/Rectangular
- Nominal diameter: DN____ (rectangle write width × height)
- Design temperature: ____℃ (sustained) /____℃ (instantaneous peak)
- Design pressure: ____kPa (positive/negative)
- Displacement requirements: axial ____mm, transverse ____mm, angular displacement ____°
- Media composition: sulfur/dust/corrosive gas (specific composition)
- Connection Method: Welding/Flange (Flange Standard and Pressure Class)
- Installation space: Length limit ____mm
- Desired material: metal (304/316L/254SMO, etc.) or non-metal (fluororubber/silicone/PTFE, etc.)
- Whether a deflector is required: Yes/No; Whether insulation is required: Yes/No
- Fatigue life requirement: ____ times (general requirement ≥1000 times)
When you send these data, most manufacturers will actively recommend the appropriate model, instead of asking you if you want a "general-purpose type". If the manufacturer asks you "how much is your budget", you will say "quote first, and the performance will be given priority".
Alas, to be honest, it is not so mysterious to choose industrial sintered flue expansion joints. Understand the working conditions thoroughly and put the installation specifications in place, which can be used for ten years. I am afraid that you will come up and say "I want the best"-the best is not the best fit. If you collect this article well, you can avoid at least 90% of the pits by doing it directly next time you select the model. The remaining 10%, by experience and luck. But now that you see this, at least the luck won't be too bad.