Why do you have to install metal expansion joints in boiler bypass flue?
Think about it. In the bypass flue, the temperature of the flue gas can always be 500 to 600 or even higher, and there is fly ash. The displacement of thermal expansion and cold contraction of the pipe is not small. If the expansion joint is not used, the pipe is carried hard, and either the weld is cracked or the boiler body is broken. Used by our power station industryCorrugated expansion joint for power station industryIt is specialized in this work, which can not only absorb axial and lateral displacement, but also carry high temperatures. To put it bluntly, this is to put a "spring joint" on the pipe, let it expand and contract freely, and don't put any effort on the boiler.
What are the easiest pits to step on when selecting a model?
Many people only stare at the caliber and pressure, and when they come up, they ask, "How much is DN? How much is the pressure?" Alas, this pit makes me feel distressed. Bypass flues are mostly rectangular pipes, so you have to go upMetal rectangular expansion jointOr withThe double straight pipe bypasses the pressure balanced expansion joint to cope with large displacements. You just look at the caliber, not the displacement direction and compensation amount. When you install it and turn it on, the pipe will die, and it will be too late to regret it.
Furthermore, when the medium temperature exceeds 400℃, ordinary stainless steel bellows may creep, so it is necessary to useHigh temperature axial expansion jointThe material should be upgraded to Inconel or heat resistant steel. Don't just save that little money and end up scrapping it in half a year. The gain is not worth the loss, right? Also, the guide tube cannot be saved. Think about it, without the guide tube, the airflow directly washes the bellows, and the life swishes down-doesn't that mean getting a person shirtless and fly ashed?
Installation and routine maintenance
Be sure to adjust the tie rod nut in place before installation, and don't let the pre-compression during transportation stifle. How exactly to adjust? Referring to what we said earlierHow to adjust the tie rod nut of expansion joint, distinguish whether it is axial or lateral compensation, and don't install it backwards. If you put it backwards, the expansion joint won't work at all, and it is as awkward as wearing pants backwards.
At the beginning of operation, pay attention to whether there is any abnormal sound, which is a precursor to the loosening of the guide tube or the fall of the liner. Check the bellows surface every two months for cracks or corrosion pits, especially near welds. Do you think this is a simple job? But some people don't look at it for a year, and they panic when they leak it.
How to choose between metal expansion joint and non-metal expansion joint?
"Can you use non-metal ones?” Non-metallic expansion joints (i.e.Non-metallic expansion joints (fabric fiber expansion joints) have good flexibility and low cost, but they cannot withstand high temperature and high pressure. In the high temperature and high dust environment of the bypass flue, the non-metallic fiber layer is quickly worn out. How long do you guess? Three months could be over. Although the metal ones are more expensive, they are temperature-resistant, pressure-resistant and long-lived, especially oursThe corrugated expansion joint used in power station industry has a design life of more than 10 years.
However, if there is strongly corrosive flue gas in the pipeline, such as wet flue gas after desulfurization, then you can considerPTFE-lined hoses orPTFE Compensator. These things are top-notch in corrosion resistance, but the price has also gone up, depending on your budget and working conditions. After all, choosing metal or non-metal depends on the temperature, pressure and medium. Don't pat your head to decide.
Common Troubleshooting-Don't Panic, See What's Going On First
The cracking of bellows is mostly caused by fatigue or stress concentration. Check whether it is forcibly matched during installation. Think about it, if the pipe is hard screwed on the bolts, the bellows will be subjected to extra force every day. Can it not crack? The deflector tube falls off often because the fixed solder joint is not firm enough, or the flue gas flow rate is too high. Once you find that the expansion joint leaks, don't rush to change it. Let's see if you can repair the welding first. If you can't, replace it with a new part. Remember, the boiler must be stopped during maintenance,Flue gas baffle door closed tightly, safety first. If it is not closed tightly and people go in to overhaul it, it is no joke.
Two days ago, I met a customer, saying that the expansion joint leaked after two years of use. I asked him to take a photo and see that the deflector had fallen off long ago, and the bellows was directly worn out by fly ash. Do you say you can blame the product for this? At the beginning of the selection, there was no deflector, which saved a small amount of money and lost a lot of money. Therefore, when choosing expansion joints, don't just look at the price, you have to understand the working conditions before starting.