The first step is to find out the background of your flue: temperature, medium and displacement must all be missed
What are you most afraid of when you engage in large expansion joints in power plant flues? I am afraid that you will buy it blindly without even figuring out what is going on in your own flue. Two days ago, a customer came to me in a hurry, saying that the expansion joint cracked after less than half a year. I asked him three numbers-flue gas temperature, media composition, and pipe displacement, but I couldn't answer any of them. Do you think this can be done without any accident?
TemperatureThis is the worst thing. Is your flue before or after desulfurization? Before desulfurization, the flue gas temperature can reach 150℃ or even higher, and after desulfurization, it is only fifty or sixty degrees. When the temperature is high, the skin of non-metallic expansion joint has to choose high-temperature resistant silicone cloth or fluororubber cloth; The temperature is low, and a regular rubber compensator can make do. But don't get confused,Corrugated expansion joint for power station industryAndThe high temperature axial type expansion joint applies to different temperature ranges. If the upper temperature limit is exceeded, the bellows will be directly fatigued and fractured.
MediumNor can you be sloppy. Are there sulfur-containing corrosive gases in the flue? Are there any dust particles? If corrosive, you have to considerPTFE-lined hoseOrPTFE compensator。 If there is much dust, the deflector is particularly critical-let's talk about it later.
And finallydisplacement amount。 Lateral displacement, axial displacement, angular displacement, you have to take a ruler to measure it, or look for design drawings. Don't estimate by feeling, it's biased when you estimate. The displacement amount is not accurate, and the expansion joint selection will directly overturn the car. If you don't believe me, ask those pretendingStraight pipe pressure balanced expansion jointBuddy, which one didn't calculate the displacement before daring to place an order?
The second step is to choose the type: metal rectangular expansion joint or non-metal expansion joint? Don't choose the wrong one
Knowing the parameters, the next step is to select the type. Most of the flues in power plants are rectangular flues, so the common ones areMetal rectangular expansion jointAndNon-metallic expansion joints (fabric fiber expansion joints)。 How do you choose between these two?
Let's start with the metal rectangular expansion joint. It is resistant to high pressure and high temperature, and is suitable for positive pressure flue, such as the section from the outlet of induced draft fan to desulfurization tower. But there is a dead hole-it can't absorb too much lateral displacement. If the flue expands and contracts very badly, the metal rectangular expansion joint can carry a few millimeters at most, and it will deform if it is bigger. That's when you have to use itCompound hinge transverse expansion jointOrLarge tie rod expansion jointTo combine absorption.
Let's talk about non-metallic expansion joints. It is cheap, easy to install, and can also isolate vibration and reduce noise, especially suitable for flue in negative pressure section. The disadvantage is that it is not pressure-resistant, so don't think about it if the pressure exceeds 0.1MPa. In addition, it is afraid of sharp objects scratching, so you have to be careful when installing it. Oh, yeah,Rectangular non-metallic expansion jointThe standard is JB/T 12235-2015. When you purchase, you can ask the manufacturer for this standard number, so as not to buy three-no products.
Then which one to choose? Let me give you a formula:Metal for high temperature and high pressure, non-metal for low pressure and negative pressure, and hinge combination for large lateral displacement.This is the experience of an old mage in the industry. You should remember it.
The third step is to do three things before installation: check the guide tube, adjust the pull rod, and look for the direction of the arrow
When the expansion joint is transported to the site, don't rush to weld it to the flue. Do three things first, and don't mess with the order.
First thing: check the deflector.The function of the guide tube is to guide the flue gas to flow smoothly and prevent the impact of the bellows. When you open the package, first see if the direction of the guide tube is correct. The open end of the guide tube should be facing the direction of flue gas flow, and if it is installed backwards, it is equivalent to white. I saw a construction site before where the deflector was installed backwards, and the bellows were punched through in three months. You say it was wrong or not?
Second piece: adjustable pull rod.When the expansion joint leaves the factory, the tie rod is generally adjusted to the installation length. But it may come loose during shipping. You have to use a wrench to adjust the tie rod nut so that the actual length of the expansion joint is equal to the installation length required by the design. Note:Does the screw of the expansion joint need to be removed?The answer is-can't be disassembled before installation! The tie rod is temporarily fixed to prevent distortion of the expansion joint during transportation and hoisting. Wait until it is welded before it can be disassembled. How to tune it?How to adjust the tie rod nut of expansion joint: First loosen the locking nut, rotate the adjustment nut to compress or stretch the length of the expansion joint to the specified size, and then lock tightly.
Third: Look for the direction of the arrow.Expansion joints are usually marked with arrows indicating the direction of media flow. The direction of this arrow must coincide with the direction of the flue airflow. Someone asked: Which way does the arrow go? It is very simple. Look where the arrow points, and the smoke goes. If it is installed backwards, the bellows will bear the reverse impact force, and the life will be greatly reduced.
The fourth step, on-site installation practical operation: hoisting, centering, welding, and removing the tie rod. If the sequence is chaotic, accidents will happen
After the preparations are finished, start loading. Remember this order:Hoisting-> Centering-> Welding-> Removing Tie Rod。 Not a single step wrong.
hoist: Use a sling to hoist, don't use a wire rope to directly strangle the expansion joint, otherwise the skin or bellows will be strangled. The lifting point should be right, and it is best to hang it on the flange or lug. Non-metallic expansion joints are particularly delicate, so don't touch sharp corners when hoisting.
Centering: Place the expansion joint between the flue interface and adjust the position so that the flange holes at both ends are aligned. Don't pull hard, just fine-tune the gasket if it doesn't match. The centering accuracy should be controlled within ±2mm, otherwise the stress will be concentrated after welding.
weld: Fix it by spot welding first, and then weld it in sections. Note: When weldingProtect expansion joint bodyAvoid welding slag from splashing onto bellows or skin. Can be covered with a refractory cloth. If it is a non-metallic expansion joint, the welding temperature should not be too high. It is best to weld away from the expansion joint or separate it with heat insulation.
pull-off rod: This is the last step. Many newcomers do the opposite, first remove the tie rod and then weld it. As a result, the expansion joint is twisted and deformed as soon as it is stressed. Remember:Does the screw of the expansion joint need to be removed?— — After the welding is finished and the weld seam cools, remove the tie rod. When removing, symmetrically loosen the nut and let the expansion joint slowly release to the working state. Check the displacement indicator after disassembly to ensure that the expansion joint has enough compensation space.
Bonus: Keep an eye on these three places for daily maintenance, otherwise it will be easy to poke lous
Just put it up and forget it? How can it be so worry-free. If no one takes care of the large expansion joint in the flue of the power plant, something will happen sooner or later. You focus on these three places:
- Skin or bellows surface: Check once a month for bulges, cracks, corrosion spots. The non-metallic skin will harden when it ages and shatter when it is pinched, so it is time to replace it. If there is fatigue crack in the metal bellows, contact the manufacturer quickly to change it.
- guide tube: Deflector wear is common, especially dusty flues. If you shine it with a flashlight, if the guide tube is worn out, the smoke will go directly to the bellows and be scrapped soon.Specific Function of Expansion Joint Guide TubeIt is protection. Once it fails, it must be replaced with a new one.
- Tie rods and bolts: Although the tie rod is removed, some double tie rod expansion joints still retain the limit bolts. Check for looseness and rust. Do anti-corrosion treatment once a year and paint anti-rust paint.
To say a thousand words, the large expansion joint of the flue of the power plant is not high-tech, but every step hides a pit. From selection to installation to routine maintenance, you can take at least half of the detours by following these four steps. If you are unsure, ask us directly. Don't shoulder it yourself.