Step 1: Don't rush to buy it, find out which expansion joint to use in the flue
Two days ago, a buddy called in a hurry and said that the expansion joint cracked after two days of installation. I asked him what model he bought, and he said, "Just that kind of metal". Tsk, you know something bad is going to happen. The temperature in the flue of the power plant is high, and the flue gas is highly corrosive, so it is not just a general-purpose corrugated expansion joint that can be made do.
You have to see if the flue is round or square first. You have to use a rectangular flueMetal rectangular expansion jointOrRectangular non-metallic expansion joint(The fabric fiber kind). Round flue? Then there's a lot of choice —Corrugated expansion joint for power station industry、High temperature axial expansion joint、Universal corrugated expansion jointIt can be packed, but it depends on the medium temperature. Over 400℃? Don't think about it, honestly non-metallic, or with insulationHigh temperature axial expansion joint。
Desulfurization flue. After wet desulfurization, the flue gas is acid and wet, and ordinary bellows can't bear it. At this timeDesulfurization flue gas baffle doorCooperateNon-metallic expansion jointThat's the right answer. If the flue has a lateral displacement or needs to absorb vibration, it must be consideredCompound hinge transverse expansion jointOrCurved tube pressure balance expansion joint。 To put it bluntly, don't rely on guessing when selecting a model. It's better than anything else to find out the flue parameters (temperature, pressure, displacement direction, medium composition) before placing an order.
Step 2: Before installation, these 3 details can save you half the rework time
Don't rush to unpack the stuff when you buy it. Do three things first:
- Check product nameplates and drawings.There is usually an arrow on the expansion joint, which is the direction of the medium flow. Install backwards? Then the guide tube becomes a "blocking tube" and waits for air leakage.
- Check the tie rods and nuts.The tie rod may be tightened and fixed during transportation. You must confirm that the factory pre-tension value is still there. If you loosen it casually, the displacement will not match, and it will be broken as soon as you turn it on. Refer to the question and answer "How to adjust the tie rod nut of the expansion joint" on our station, which is very detailed.
- Look at that direction of the deflector.The function of the guide tube is to guide the medium and protect the bellows from being washed. If the guide tube is installed backwards, or it is squeezed and deformed during installation, then the expansion joint is basically half wasted. We have previously written "The Specific Function of Expansion Joint Guide Tube", you can flip through it.
In addition, the size of the flue opening and the flatness of the flange surface must be checked. And guess what? Many people ignore the parallelism of the flange surface. As a result, when the bolts are tightened, the expansion joint is twisted into a "twist". Leveling? Sweep it with a level. If the difference exceeds 2mm, the gasket will be leveled. Don't be too troubled.
Step 3: Install by hand, and it is useless to turn the bolts in reverse order
Bolt tightening is a job that looks simple, but it is actually easiest to roll over. Don't come up and screw the opposite corner with a wrench-that's the old way of fitting tires, and fitting expansion joints doesn't work. The correct action is:First, put all the bolts on by hand, and then tighten them gradually in three steps according to the cross method。 Screw to 30% torque the first time, 60% the second time, 100% the third time. And it has to be twisted in circles every time, instead of twisting one side first and then twisting the other side.
Why? Because the flange surface of the expansion joint is a flexible connection, if you screw one end to death, the other end will tilt up. If the gasket is not compressed, air leakage is a small matter, and the cracking caused by uneven force of the bellows is a big problem. Tip: After tightening, use a flashlight to shine it from the back of the flange to see if there are any light-transmitting gaps. Got a gap? Disassemble it and level it again.
Step 4: Adjust the pull rod and guide tube, and don't let the expansion joint become a "top beam column"
Expansion joints are not load bearing pieces! The purpose of the adjustment rod is justLimiting excessive displacementInstead of having the tie rod carry the weight of the pipe. Many on-site diagrams save trouble, and the tie rod is used as a hanger. As a result, the tie rod nut eats dead force, the expansion joint can't move at all, and the displacement is all stuck on the bellows-it's weird if it's not bad.
After installation, first loosen the locking nut on the tie rod to allow the expansion joint to be in a free state. Then according to the design displacement, adjust the length of the tie rod according to the drawing. Note: When adjusting, let the nuts at both ends of the tie rod be screwed in or out at the same time to ensure uniform force. How exactly to adjust? Refer to the Q&A on our site "The Function of Expansion Joint Tie Rod" and "The Correct Installation Method of Large Tie Rod Expansion Joint".
The clearance of the guide tube should also be checked. An expansion gap of 5-10mm must be left between the guide tube and the bellows, otherwise the guide tube will squeeze the bellows during thermal expansion and contraction. It's not a hard job, just stick a gauge in it.
Step 5: Pay attention to these two places after turning on, which can be used for several years
Finally installed, boot up for trial run. Don't leave in a hurry. Staring at two places:
- Whether there is any abnormal deformation of the expansion joint body.In the first half hour of turning on, the temperature rises sharply and the bellows will expand. If you find that the wave pitch of a corrugation suddenly becomes larger or smaller, it means that the displacement is not evenly absorbed, and stop the machine quickly to check the tie rod and fixed bracket.
- Whether there is smoke or dripping at the flange connection.The flue gas temperature is high, and the leak can be seen at a glance. If there is only slight smoke, it may be that the gasket is not crushed. Tighten the bolts again after stopping the machine (remember to follow the cross method). If there is a large amount of air leakage, you have to disassemble it to see if the guide tube has been flushed askew.
In addition, check the bolt torque once after one week of operation. Thermal expansion and contraction will drop a lot of initial torque. Be careful not to twist when tightening, otherwise the stress of the bellows will be concentrated and the life will be cut in half directly. Properly maintained, aNon-metallic expansion jointIt's fine to use it for three to five years, and the metal one can even last for seven or eight years.
The installation of expansion joints in the flue of power plants depends on quality in three points and installation in seven points. Choose the right, install the right, and adjust the right, and the rest is all worry-free. If one step goes lazy — guess what? The labor cost of rework is enough to buy several new expansion joints.