First, understand what kind of deformation the flue expansion joint should carry (axial, transverse, angular, don't confuse)
When you open the drawing or the flue scene, the expansion joint that you see actually has to carry three kinds of deformation instead of one:Axial deformation、Lateral deformation、Angular deformation。 To put it bluntly, the pipe will expand and contract along the axis, deflect left and right, and tilt like a seesaw. What about that? You score clearly.
Axial deformationMost commonly, it is the length change caused by thermal expansion and contraction of pipes. For example, after a boiler is started, the chimney outlet can retreat by tens of millimeters, which is the axial change. When measuring, you mark two points on the pipe to see if their distance has changed.
Lateral deformationTo put it bluntly, the pipe was "screwed" in the horizontal direction. For example, the flue at the outlet of the fan will sway left and right due to vibration and lateral wind load. At this time, you have to consider the choice of modelCompound hinge transverse expansion jointOrLarge tie rod expansion jointTo absorb this displacement.
Angular deformationMore concealed, it is common in pipe corners or uneven heating of vertical pipes, resulting in angular deflection of pipe sections. If you take a square and measure it, you find that the flange surfaces are not parallel, which is the angular displacement. When you encounter this kind of thing, you must useCurved tube pressure balance expansion jointOrCompound straight pipe bypass pressure balanced expansion joint。
Many projects are only calculated according to the axial direction, but after installation, it is found that the pipe is holding up or the bellows is blown-just because the lateral and angular directions are not considered. Don't be too troublesome. All three kinds of deformation have to be calculated, even if one value is estimated, there must be a basis.
2. On-site measured pipeline displacement data-take a ruler, measure the mark, calculate the net value, and teach it step by step
If you don't go to the site for testing, you will probably overturn by relying on the drawings alone. Two days ago, I met a customer and said that "the thermal expansion was 50mm written on the drawing". As a result, when I went to the site, the actual displacement of the pipe was only 38mm, because the bracket friction and elbow compensation consumed part of the displacement. What about that? Take your own ruler and do it.
Step 1: Make marks.Choose two stable points on the pipe, such as the middle of two flanges or two fixed brackets, draw a cross with a marker, and it is best to weld a small iron sheet. The distance between the two marks, you take a steel tape measure, the reading is accurate to millimeters, and note it down. This is called "cold distance".
Step 2: Wait for the working condition to be stable.After the pipeline runs to the normal temperature (for example, the flue gas temperature is 350℃), wait for more than half an hour to allow the heat to expand fully. Then take the ruler and measure the distance between the two marks again. It's called "thermal distance". Pay attention to safety, don't burn it, and use an infrared thermometer to confirm the temperature if necessary.
Step 3: Calculate Net Worth.The hot distance minus the cold distance is the axial displacement. What about lateral displacement? You pull a vertical line on the side of the pipe to see how much the pipe centerline is offset; Or make a horizontal line with a laser rangefinder. What about angular displacement? Use an angle gauge to measure the inclination angle of the flange surface.
If there is aFlue gas baffle doorOrManual plug-in insulation doorWhen testing, ensure that the door panel is in a fully open position, otherwise it will block the flow of smoke and lead to inaccurate displacement measurement. Also, if there is dust accumulation in the flue, clean it first and then test it, because dust accumulation will affect heat conduction and displacement.
Why emphasize "calculating net worth"? Because the pipe may already be pre-biased when it is cold. For example, the manufacturer has deliberately left the pre-stretching amount during installation. If you directly measure the cold state to the hot state, you may get the "apparent displacement", not the real thermal displacement. Therefore, it is best to measure three sets of data: during installation (cold state), steady state of operation (hot state), and after shutting down and cooling (re-cold state), the real net displacement is subtracted by hot state (cold state + pre-bias).
3. Select products according to the deformation quantity: how to match high-temperature axial, rectangular non-metallic and corrugated expansion joints for power stations?
The data has been measured back, and all three kinds of deformation have been figured out. The next step is to select products. Don't choose randomly, you have to take your seat according to the working conditions.
High temperature axial expansion joint— — Straight pipe sections that are most suitable for pure axial expansion and contraction, such as the main steam pipe of power plants and the boiler outlet flue. Its bellows wall thickness, high temperature resistance, and some with multi-layer structure. If your measured axial displacement is large and the lateral and angular directions are almost 0, choose it directly. But be aware that it cannot withstand lateral and angular directions, so the pipe must be centered when installing, otherwise it is easy to wear off.
Rectangular non-metallic expansion joint— — This good thing is specially used for rectangular flues, such as the inlet and outlet of desulfurization tower and the inlet and outlet of dust collector. Because the structure is square, metal bellows are difficult to make, and non-metal (fabric fibers) can absorb three-dimensional displacement. Your measured lateral and angular displacements are relatively large, so you have to goRectangular non-metallic expansion jointOrNon-metallic expansion joint (fabric fiber expansion joint)。 It is not afraid of misalignment and can be corrosion resistant. The disadvantage is that it cannot bear pressure (it can only be used in low pressure section).
Corrugated expansion joint for power station industry— — This name is broad, but it specifically refers to the metal bellows used in high-temperature and high-pressure occasions such as the main flue, reheating hot section and cold section of power stations. It takes into account both axial and lateral directions, but its angular capability is average. If your pipe has both axial and transverse directions (such as an air-cooled island vacuum pipe), considerDouble hinge expansion joint for air-cooled island vacuum pipelineOrCompound hinge transverse expansion joint, they absorb lateral displacement with a hinge structure, while the tie rod limits axial overdisplacement.
Oh, by the way, andUniversal corrugated expansion jointThis is a panacea, suitable for occasions where the temperature is not high and the pressure is not high. However, do not use it in the high-temperature flue gas section, otherwise the bellows may fail fatigue soon.
How to match it? Here's a simple formula for you:
-Pure axial → high temperature axial type expansion joint
-Rectangular flue, multi-directional displacement → rectangular non-metallic expansion joint
-High temperature and high pressure, mainly axial in power station → Corrugated expansion joint for power station industry
-There is lateral displacement and the pipe is circular → double hinge transverse type expansion joint or large tie rod expansion joint
-with angular displacement and pressure balancing required → curved tube pressure balancing type expansion joint
Don't forget to look at the temperature. If the flue gas temperature exceeds 600℃, the metal bellows need to be insulated or used withNon-metallic expansion joint。 If the temperature is below 100°C, a rubber compensator can also be considered, but the wear resistance is not as good as non-metallic.
4. Practical skills of reserving deformation during installation: Don't screw the tie rod nut to death, and don't reverse the direction of the guide tube
After choosing the product, you have to install it right. Many on-site accidents are loaded wrong. Let's talk directly about the two most critical practical details.
First, don't screw the tie rod nut to death.What is the tie rod (also called limit screw) on the expansion joint for? Prevents the bellows from being overstretched during transport and installation. Once installed in place, you should loosen the nut to the predetermined clearance according to the measured axial displacement. For example, the maximum axial compensation of your expansion joint is 80mm, and the measured thermal displacement is 60mm. Then you loosen the nut to leave a gap of about 60mm (or adjust it according to the pre-stretching amount given by the manufacturer). Specific operation: First loosen the locking nut, then rotate the adjusting nut, measure the exposed length of the pull rod with a caliper, and adjust to the design value. After adjustment, tighten the locking nut again, but don't force too hard to prevent the thread from slipping. You can take a look at the Q&A of "How to Adjust the Tie Rod Nut of the Expansion Joint" on our station, which is illustrated.
Second, don't reverse the direction of the guide tube.Specific Function of Expansion Joint Guide TubeIs to guide the flow direction of the medium and reduce vortex and wear. The small opening (narrowed end) of the guide tube must face the direction in which the medium flows. That is, if the smoke flows from left to right, the small opening of the guide tube is on the left and the large opening is on the right. Install it backwards, anyway, the smoke directly washes the bellows, and it will wear out in a few months. Remember: Look at the direction of the arrow (many products have arrows when they leave the factory). If there is no arrow, you mark one yourself or ask the manufacturer. Be sure to confirm before installation, don't rely on your feeling.
-If it is a metal bellows, remove the transportation limiting device (such as transportation bolts and pads) after installation, otherwise the bellows cannot deform freely.
-If it is a non-metallic expansion joint, be careful not to scratch the fabric layer and protect it with a soft cushion when installing.
-The pipe support point should be set at a place other than 200mm away from the expansion joint to avoid the expansion joint bearing the pipe's own weight.
-forDirect buried (fully buried) type expansion jointBefore installation, anti-corrosion and heat preservation must be done, and the backfill soil should be tamped in layers. Don't let the stones squeeze into the bellows.
5. How to verify whether the deformation is enough after installation? Look at corrugation compression and measure temperature change, three simple tricks
It doesn't mean everything will be fine if you are done. You have to verify whether the expansion joint can eat the deformation amount under actual working conditions. Don't wait until you miss it before you regret it. Three tricks.
First trick: Look at the amount of ripple compression.After running it for a while (say a week later), the furnace is shut down to cool down, and you go to see the bellows of the expansion joint. Use a caliper to measure the spacing between the ripples, or just use a scale to measure the total length. If the corrugation is almost flattened (for example, the remaining spacing is less than 20% of the original spacing), it means that the selection is too small or the reserve is not enough, and fatigue fracture may soon occur. If the corrugation doesn't move much (the compression amount is less than 30% of the design value), it means that the actual thermal displacement is smaller than you measured, no problem. However, if it is a non-metallic expansion joint, you can see if the outer fabric has any bulging or wrinkles. If so, it is excessive displacement.
The second trick: measure the temperature change.Use infrared thermal imaging camera or contact thermometer to measure the surface temperature of the expansion joint. If the temperature of a certain part is obviously high (for example, more than 50℃ higher than that of the adjacent pipeline), it means that the medium has generated vortex or erosion inside the expansion joint, which may be because the guide tube is installed backwards or dust accumulates inside the bellows. In addition, if the local temperature difference on the surface of the metal bellows exceeds 30°C, thermal stress cracks may have occurred.
The third trick: listen to the sound and watch the leak.During the operation, take the listening stick to listen to whether there is a hissing sound near the expansion joint. It may be that the bellows is leaking. Or apply soapy water to the bellows weld to see if there are bubbles. If it leaks, it has to be replaced quickly, otherwise the pressure of the whole system will fluctuate, and even the baffle door will be damaged.
Simple right? You don't have to buy any high-end instruments, just a ruler, a thermometer and a piece of soapy water, and you can judge whether it is installed correctly. If you find that the amount of deformation is not enough, don't panic-many times it is because the tie rod nut is not adjusted in place during installation, and it can be solved by readjusting it. If it does exceed the amount, then you can only switch to a product with a larger compensation amount.
The amount of flue expansion joint deformation can't really be patted on the head. You follow the steps above and at least you won't go wrong.