Step 1: Find out the "temper" of your flue first-temperature, pressure and displacement can't be less
Alas, I have met several customers these days, and they asked, "Which brand of boiler flue expansion joint has better performance?"-Let's not worry, the brand is the last one to look at. You don't even know what the working condition of your flue is, so it is useless to buy back the good expansion joint. Just like wearing shoes, you don't know how big your feet are and what your walking habits are. No matter how expensive you are, you have to grind your feet.
The first thing you have to do now is to go to the site and measure three numbers:Maximum temperature, working pressure, and possible displacement of the pipe。 Don't just look at the design drawings, the actual operating temperature is often quite different from the design value. Temperature is the key to determine the life of materials. Beyond the tolerance limit, metal bellows will crack fatigue in minutes. Pressure, choose non-metal at low pressure, and metal at high pressure. This will be described later. The displacement includes axial, lateral and angular displacements. You have to figure out which direction and how far the flue runs, otherwise the expansion joint can't "eat" at all.
For example, last year there was a power plant customer whose flue temperature was measured at 650℃. They wanted to use ordinaryNon-metallic expansion joint (fabric fiber expansion joint), I quickly stopped it-the fabric fiber can be carried to about 400℃ at most, and it will be carbonized if it exceeds it. I finally recommended it to themHigh temperature axial expansion jointWith heat-resistant alloy steel, this is stable. So, don't bother, find out the "temper" before you start.
Tips:If you are really unsure of the displacement, you can take an iron wire to simulate the direction of the flue, draw lines in the cold state and the hot state respectively, and you will know the general displacement direction by comparison.
Step 2: Wrong material, performance in vain-metal expansion joint or non-metal expansion joint?
Okay, we have the working condition data. Next, choose the material. This link is the most tangled, becausePerformance of Boiler Flue Expansion JointMore than half of it depends on material selection. Metallic or non-metallic? Don't worry about it. Listen to me.
Metal expansion joint(e.g.Universal corrugated expansion joint、Straight pipe pressure balanced expansion joint、Compound hinge transverse expansion jointThese) have the advantages of high pressure resistance, long service life, and are suitable for high temperature and high pressure occasions. But metal is afraid of corrosion! The flue gas contains sulfur and chlorine. If you think about it, stainless steel can't withstand long-term acid etching. If it's a desulfurization flue, you have to usePTFE-lined hoseOrPTFE compensatoror simply chooseNon-metallic expansion joint (fabric fiber expansion joint)。
The advantages of non-metal are precisely corrosion resistance, large compensation, good vibration reduction, and cheap. The disadvantage is that it is not resistant to high pressure and ultra-high temperature. Generally, the flue gas temperature is lower than 400℃, the pressure is below 0.1MPa, and non-metal is appropriate. Such asRectangular non-metallic expansion jointSpecially equipped with rectangular flue, the installation is also hassle-free. But note: There are national standards for non-metallic expansion jointsJB/T 12235-2015Look for this when you buy it.
Then how do you choose? Here's a rough rule:High pressure, high temperature (> 400℃), large pipe diameterMetal selection;Low pressure, low temperature, large displacement, strong corrosionChoose non-metallic. If you are really unsure, ask both manufacturers and ask them to calculate the fatigue life according to your working conditions-anyway, we often do this and won't charge more.
Step 3: Install pit stepping guide-how to do the guide tube orientation, tie rod nut and arrow direction?
I bought the right expansion joint, but I still scrapped it if I installed it wrong. Two days ago, a customer sent a photo, and the guide tube was installed backwards. As a result, the backward airflow blew the bellows loudly, and it leaked in three days. You say it was wrong or not?
Let's talkguide tube。 Its function is to guide the smoke along the flow direction and protect the bellows from being washed by high-speed airflow. Remember:The direction of that opening of the guide tube must be consistent with the direction of flue gas flow。 How to judge? Look at the arrow on the barrel. Generally, the expansion joint housing will be marked with an arrow (some are marked on the nameplate), and that arrow is the flow direction of the medium. Don't take it for granted that the arrow refers to the installation direction, it just tells you "this is the import".
Let's talktie rod nut。 This pit has the most! Many masters don't remove the tie rod nut after installing it, and as a result, the expansion joint can't move at all, which is equivalent to installing a "dead joint". The role of the tie rod nut is to fix the bellows during transportation and installation, preventing accidental deformation. After all the pipes are in place, the welding is completed, and the flange is tightened,The tie rod nut must be loosenedGenerally, it is loose enough that there is a gap of 2~3mm between the nut and the ear plate. But note: if it is with a tie rodLarge tie rod expansion jointThe tie rod itself is used to withstand the internal pressure thrust, and that nut cannot be completely removed, but can only be adjusted to the pre-tension/pre-compression position. Look at our official websiteHow to adjust the tie rod nut of expansion jointThat question and answer, there is a detailed illustration.
AndArrow Direction。 In addition to the deflector arrow, some expansion joints (such asExternal pressure single axial expansion joint) will also mark the flow direction arrow, which is to remind you that the medium should flow through the outside of the bellows, not the opposite way. Anyway,All markings should be read clearly before installationDon't wait for it to be installed before reworking.
Note:Never use welding current to penetrate the bellows during installation! First block the bellows with asbestos cloth or iron sheet, and then weld the flange. We have encountered cases where welding slag splashed and burned the bellows, and the whole expansion joint was directly scrapped.
Step 4: Details of routine maintenance that quietly ruin performance — corrosion, dust buildup, fatigue life
You think everything will be fine when you install it? Wrong. No matter how good the performance of the boiler flue expansion joint is, it can't stand the "three mountains": corrosion, ash accumulation and fatigue.
Let's startcorrosion。 Sulfur dioxide in flue gas becomes sulfurous acid when it encounters water, which is a chronic poison for metal bellows. If you are usingNon-metallic expansion joint (fabric fiber expansion joint)Pay attention to check whether the outer fluororubber or silicone coating has aged and cracked. Once a week, take a flashlight to shine on the inner and outer walls of the bellows. If you see rust spots or small holes, contact the manufacturer to replace it. Don't delay, the corrosion will spread like cancer cells.
And then there'sAsh accumulation。 Smoke and dust will accumulate inside many expansion joints, especially the gap between the guide tube and the bellows. When there is too much ash, the bellows will be stuck, resulting in the failure of the compensation function. What to do? Periodically purge with compressed air from the access port, or design with a soot blowing interface reserved. RightMetal rectangular expansion jointThis kind of large-section products, the problem of dust accumulation is more prominent, and it should be focused on.
And finallyFatigue life。 Every time the boiler is started or stopped, the expansion joint undergoes a thermal expansion and contraction. The design life is generally 1000~3000 cycles, depending on the specific working conditions. If you do the math, if you start and stop once a day, it will be a thousand times in three years. It is recommended to make a ledger, record the installation date and the number of starts and stops, and plan the replacement in advance when it reaches almost 80% of the design life. Don't wait until it leaks before replacing it. At that time, even the baffle door and smoke baffle door may suffer.
Okay, you can finish the above four steps, and the performance of the boiler flue expansion joint is basically grasped. If you still don't understand anything, look directly at our official website product page — —Corrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement Industry、Desulfurization flue gas baffle doorThese classifications have detailed parameters below, or you can directly call the technology, don't guess yourself.