Step 1: Find out exactly what kind of expansion joint you need for your flue-don't just pick the model
"Do you have an expansion joint? Give me one." You asked him what equipment it was used on, and he said million unit flue. Good guy, the flue of the million unit is high in temperature, large in diameter, and there is sulfur and dust in the flue gas. You can't just find a bellows and get it on. Think about it, if you take an ordinary rubber compensator on it, it will melt in two days. Not only will the money be wasted, but the loss of shutting down for emergency repair will not be a little.
Then how do you choose? You have to look at the actual situation of your flue first:
-Temperature range: Is it a continuous 300°C or an occasional 600°C rush?
-Medium corrosivity: Wet smoke or dry smoke? Is there a desulfurization system?
-displacement direction: Is it more axial expansion and contraction or lateral oscillation?
For millions of machine flues, the common ones are as follows:Metal rectangular expansion joint(Suitable for square flue, low pressure but large compensation amount),Non-metallic expansion joint(That is, fabric fiber expansion joint, high temperature resistance, good vibration reduction, suitable for large diameter rectangular flue),Corrugated expansion joint for power station industry(Circular flue, high pressure occasion).
Two days ago, there was a power plant user. The flue was square, the temperature was 450℃, and the flue gas contained sulfur. He initially wanted to use a metal rectangular expansion joint, but I suggested that he use a non-metal expansion joint. Why? Because that non-metallic layer can withstand acidic smoke, and the square flue is easier to seal with non-metals. You see, if you don't think through the first step, the rest is all in vain.
Step 2: Staring at these 3 parameters when selecting, one less is easy to overturn
After determining the type, don't rush to place an order. You have to report these three figures to the manufacturer:Design temperature, design pressure, compensation amount。 One less? Hey hey, the probability of rollover is doubled directly.
1. Temperature
The exhaust temperature of the flue of a million machines is generally 120℃ ~180℃, but some working conditions (such as soot blowing) may instantly reach above 300℃. That's when you have to chooseHigh temperature axial expansion jointOr non-metallic expansion joints with thermal insulation. If the temperature is selected low, the bellows will accelerate fatigue and even crack.
2. Pressure
The flue pressure is usually not high, slightly positive or negative. However, if it is a wet flue after desulfurization, the pressure fluctuates greatly, so it has to be consideredCompound hinge transverse expansion jointTo absorb multidirectional displacement. If the pressure parameters are wrong, the expansion joint will be squashed or bulged.
3. Compensation Amount
You want to figure out what the total thermal elongation of the flue is, and divide it by the compensation capacity of the individual expansion joints. Don't think about one expansion joint package, sometimes you need to connect several in series, such asCompound straight pipe bypass pressure balanced expansion jointFor large axial compensation. In addition, don't forget the guide tube-it not only protects the bellows, but also reduces the erosion of the expansion joint by the medium (for specific functions, please turn over our previous Q&A).
Step 3: Preparation before installation-measuring the size, checking the direction, and removing the screw, one step is wrong, one step is wrong
Okay, the expansion joint has arrived. Don't rush to attack the flue. Listen to me and follow these three steps:
① Measure the size
Take a tape measure and measure all four sides of the flue connection, not only one side. It is normal that the actual size is sometimes three or five millimeters different from the drawing. If the size of the expansion joint is wrong, if it is hard pried on the spot, the sealing gasket will be uneven, and it will inevitably leak in the future.
② Check the direction
There is usually an arrow on the expansion joint to represent the direction of the medium flow. The direction of the arrow must be consistent with the direction of the flue flow. Especially for models with guide tubes, the opening direction of the guide tube should be facing the medium. And guess what? I have seen a factory install the arrow backwards, and as a result, the deflector is overturned by the airflow, and it is scrapped in a month.
③ Remove the screw
Many expansion joints will use screws to press and fix the bellows or fabric layer during transportation to prevent damage during transportation. After installation,The screw must be removed(Someone asked if the screw of the expansion joint needs to be removed? The answer is: it must be removed!). If it is not disassembled, the expansion joint will lose its compensation ability, which will have the same effect as welding. In addition, if you are using a large tie rod expansion joint, the tie rod nut should be adjusted to the proper position, which can't be locked or too loose (how to adjust it specifically? Refer to our previous question and answer "How to adjust the tie rod nut of expansion joint").
Step 4: Don't go in a hurry after installing it. These inspections must be done on site
The expansion joints are up and the bolts are tightened. Calling it a day? Don't worry, do four things on the spot:
- Check flange seals: Click the flange gap with a gauge. If a gauge of more than 0.5mm can be plugged into one side, it means that the bolts are not evenly tightened and have to be tightened again.
- Check for distortion of the expansion joint: Especially for non-metallic expansion joints, if the flange is crooked during installation, the fabric layer will be twisted and the life will be shortened by half.
- Verify limiting device: For expansion joints with tie rods or limit rings, adjust the nuts after installation so that the bellows have normal expansion and contraction space at the working temperature. Adjustment method: When cold, screw the nut to just contact the limit block, and then retreat half a turn to leave a thermal expansion margin.
- Cold state pre-stretch/pre-compression: Some installation ambient temperatures are low and the amount of thermal elongation of the pipe is large, which requires pre-stretching. The calculation formula is based on the length and temperature difference of the pipeline, which can be asked by the manufacturer to provide the recommended value.
Is it okay to not check? Alas, I have seen a project that turned on as soon as it was installed. As a result, two days later, there was an air leak at the flange. When I disassembled it, I saw that the deflector was blown askew. Because I didn't check the guide tube position. So don't be lazy.
Step 5: Routine maintenance Look at these 4 places, most faults can be found in advance
Once installed, the running phase also has to be watched. Let me tell you, most expansion joint failures are not suddenly broken, but are accumulated by minor problems. Focus on these four positions during your weekly inspection:
1. Bellows/Fabric Layer Surface
Metal expansion joint to see whether there are foreign objects stuck in the corrugated gap, or whether there are cracks and corrosion points. Non-metallic expansion joints see if the fabric layer is bulging, delaminated, and worn. If white powder (corrosion product) or black spots (localized overheating) are found on the surface, it must be documented and planned for replacement.
2. Guide Condition
Check whether the guide tube falls off or deforms by observing the window or disassembling the insulation layer. Once the guide tube is loosened, the high-speed airflow will flush the bellows directly, and it won't take long to perforate.
3. Flange bolts
Thermal expansion and contraction can cause the bolts to loosen. It is recommended to pull the nut with a hand after shutting down. If it can be twisted for more than half a turn, it means that the preloading force is not enough. Especially forDesulfurization flue gas baffle doorNearby expansion joints, corrosive liquids tend to leak down the bolts.
4. Displacement trajectory
Make a mark (such as a line) on the expansion joint and record the change in the position of the mark during each inspection. If it is found that the expansion joint deflects too much in a certain direction, it means that the pipeline system may have uneven settlement or the support is stuck. At this time, it is useless to just change the expansion joint, so you have to check the pipeline support.
Maintenance records must be kept well. When something goes wrong, flip through the previous inspection list, and you will know where the problem lies. Is that the truth?