Let's be clear first: What is the flue expansion joint for?
Many people think that the flue expansion joint is just a thick pipe, and it is done when connected. Alas, that's a big mistake. Its core task is one: to withstand the displacement and vibration caused by thermal expansion and contraction for you. Think about it, as soon as the flue gas pipe heats up, the pipe will stretch. What if the weld collapses without it? Who pays if the equipment is broken? To put it bluntly, it is a "flexible joint", which allows the pipe to expand and contract freely at high temperature without stifling itself.
You said you connected a smoke pipe, and the pipe stretched as soon as the temperature rose, and then retracted when it cooled down. If there is no place to release this expansion and contraction, the flange will leak at least, and the pipe will burst at worst. Flue expansion joints do this specifically-absorb axial displacement, lateral displacement, and reduce vibration and noise. Is that the truth?
Two mainstream materials, how to pick? Find out your working conditions first
The matter of choosing materials is a disaster if it is reversed. Two days ago, a customer installed a non-metallic expansion joint at the tail of the cement kiln, and it burned out in a month-big heart, brother!
Metal expansion joint: Like the one in our stationCorrugated expansion joint for power station industryOrMetal Corrugated Expansion Joints in Cement IndustryHigh temperature and high pressure resistance, suitable for dry flue gas, corrosion is not strong occasion. Places such as boiler outlets and chimney entrances, where the temperature is five to six hundred degrees or even higher, have to be made of metal.
Non-metallic expansion joints (fabric fiber expansion joints): The one we have on the siteNon-metallic expansion joint (fabric fiber expansion joint)It is cheap and has a large amount of compensation, but it is afraid of erosion and high temperature. It is suitable for desulfurization flue with wet flue gas and low temperature. If you use it as metal, you're looking for a burn.
Specific selection steps? Come on, do it:
- ① Look at the medium temperature-metal is generally considered when it exceeds 400℃, and non-metal may be more cost-effective when it is lower than 200℃.
- ② Look at the pressure-high pressure must be metal, and non-metal can't bear much pressure.
- ③ Look at the displacement direction-universal corrugated expansion joint for axial displacementUniversal corrugated expansion jointCompound hinge type for lateral displacementCompound hinge transverse expansion joint。
- ④ See if there is corrosion-if there is corrosive medium, consider lining PTFE hosePTFE-lined hoseOr PTFE compensatorPTFE compensator。
Then find the corresponding model parameters in the product manual. This step can't be saved, don't rely on your feeling.
Preparation work before installation, failing to do this step is equivalent to work for nothing
After unpacking, don't rush to load it. Check the appearance for bumps, especially pay attention to the direction of the guide tube. The function of the guide tube is toSpecific Function of Expansion Joint Guide TubeIt was talked about in-directing the airflow and preventing flushing the bellows. Install backwards, the airflow directly hits the bellows, and the life is halved.
Then, adjust the tie rod nut to the factory mark position. How to tune it?How to adjust the tie rod nut of expansion jointThere are detailed instructions in: Find the limit block, loosen the locking nut, adjust the screw to the design length and then lock it. This step is to ensure that the expansion joint does not move during transportation, and it should be restored to the working state before installation.
Tips:Before installation, the pipe bracket must be fixed to allow the expansion joint to expand and contract freely. The bracket is not fixed, and the expansion joint can't move if it wants to, which is equivalent to installing an iron pimple, so what's the use?
Keep an eye on these 3 points when hands-on installation to save rework
First, the cold-drawn value of the pipeline should be accurately calculated. The amount of pre-deformation of the expansion joint is adjusted according to the ambient temperature. For example, if it is installed in summer, the pipe will be heated and elongated in the future, so you have to leave compression space for it in advance. Don't ask me how to calculate it. There are generally cold-drawn values on the product parameter table, so just adjust them.
Second, do a good job of insulation when welding. The welding slag splashes onto the surface of the bellows, and as soon as a pit is burned, the stress concentration in the later stage will crack. Wrap the bellows with asbestos cloth, which is the basic skill.
Third, the flange connection should ensure parallel and uniform clearance. When screwing bolts, pre-tighten diagonally and tighten them three times. Don't screw them to death all at once. Note: It is strictly prohibited to use expansion joints to compensate for pipe installation deviations. That's a sign that the plumber's skill is not good, and the deadlift will be scrapped directly. The deviation is too big, rework and redo the pipeline, don't save that matter.
How to check and accept after installation? See if these 4 signals will work
Acceptance is not a formality, and it will be late to change it if something goes wrong:
- ① There is no abnormal noise after the pipeline system is pressurized-there is a hissing or tapping sound, indicating air leakage or foreign objects inside.
- ② The displacement indicator mark (if any) is within the normal range-many expansion joints are marked when they leave the factory. After running, see if it exceeds the red line.
- ③ The insulation layer does not crush the expansion joint-the insulation cotton is too thick, and the expansion joint is hooped to death. How can it move? Allow space to telescope.
- ④ After several thermal cycles, the tie rod is not obviously loose-if it is loose, it means that the initial adjustment is not in place, so re-adjust it.
And guess what? A lot of problems are exposed after running. For example, if the weld is cracked by excessive vibration, don't rush to change the expansion joint at this time. First, check whether the spacing between the brackets is too large or the position of the fixed bracket is wrong. The root of the vibration problem is often in the pipe design, and the expansion joint is just the back-breaker.
Don't be lazy in routine maintenance, say it clearly in a few words
Every three months, check the bellows surface for cracks, corrosion pits, or debris buildup. Especially non-metallic expansion joints, afraid of oil stains and sharp objects, are easy to age when stained with oil, and leak when punctured by sharp objects.
If you find that the guide tube falls off, repair the weld quickly-otherwise the airflow will directly flush the bellows and the life will be halved. Don't believe it? Look at itService life of expansion jointThere are a lot of cases in that article.
As for the replacement cycle? According to our experience, the metallic ones can last 8-10 years, and the non-metallic ones have to be replaced in 5-6 years. Depending on the working conditions-if the temperature is high and the start and stop are frequent, the life will be shorter. Check it regularly, and don't wait until it leaks before remembering to change it. At that time, the equipment will be damaged by shock.