How to determine the distance requirement of flue expansion joint? Follow these 4 steps without reworking
Two days ago, I met an installer and complained to me: a batch of flue expansion joints installed in their factory last year began to leak in less than half a year. When I disassembled them, the bellows were ground as thin as paper. When asked for the reason, it was nothing more than the wrong distance-the bracket was wrong, the guide tube was short, and the expansion joint was too close to the baffle door. Do you think this is a loss?
actuallyFlue expansion joint distance requirementsThis matter was not difficult to say, but there were a lot of people who really stepped on the trap. Today, I will take these four steps apart. If you follow it, you can save a lot of money for rework.
Step 1: Find out first what kind of expansion joint your flue is – metal rectangular or non-metal?
Don't measure the distance as soon as you get up. Think about it first, what you have in your hand isMetal rectangular expansion joint, orRectangular non-metallic expansion joint？ These two things have a huge difference in the requirements for the distance between brackets.
The metal rectangular expansion joint (such as the bellows expansion joint sold in our station) has high rigidity and can withstand a certain pressure, but its corrugated part is very delicate-if the fixed bracket is too far away, the bellows will be forcibly straightened or crushed to death when the pipe expands and contracts. WhileNon-metallic expansion joint(The kind of fabric fiber) is soft, mainly depending on fiber cloth and rubber to compensate for the displacement. It depends more on the bracket. If the distance between the guide bracket exceeds 2 meters, it will collapse by itself.
Tips:Open the equipment drawing and take a glance at the expansion joint nameplate. If the material is fabric fiber or rubber compensator, it is treated as non-metal by default; If it is stainless steel bellows, it is the metal category. This step is wrong, and the rest is all in vain.
Step 2: How to arrange the fixed bracket and the guide bracket? Distance determines success or failure
Okay, now you know what kind of expansion joint you're using. Step 2, row brackets. This is the most overlooked link.
Let's startFixed bracket。 Its function is to make the pipe segment, pressing the amount of thermal expansion to this section of the expansion joint to absorb. So here's the question – how far is the fixing bracket appropriate from the expansion joint?
According to the standard, the fixing bracket should be installed close to one side of the expansion joint, and the distance should not exceed 1 time the diameter of the pipe. For example, in the flue of DN600, it is preferable to control the fixing bracket within 600mm from the flange surface of the expansion joint. Far away? As soon as thermal expansion comes up, the middle of the pipe will bend, and the displacement of the expansion joint will not be enough.
Againguide bracket。 Its task is to ensure that the pipe only expands and contracts along the axis, and does not twist left and right. For the spacing of guide brackets, it is generally recommended that a metal rectangular expansion joint is 1.5~2 meters, and a non-metal expansion joint is 1~1.5 meters. If you think about it, if the distance between the guide brackets is enlarged to 3 meters, the pipe's own weight can press the non-metal expansion joint out of the folds.
Tsk, don't bother, find a ruler to pull the wire on the spot, draw the point and then weld the bracket. Cutting brackets during rework can be much more troublesome than cutting pipes.
Step 3: Install the expansion joint and baffle door next to each other. How much is left in the middle to avoid fighting?
In the flue system, the expansion joint is often followed byFlue gas baffle doorOrRound Flap Door (Double Seal)。 When these two things are too close, the consequence is that when the baffle door opens and closes, the blade will hit the inner wall of the expansion joint, or the expansion joint guide tube will get stuck in the baffle door.
In the most exaggerated case I have ever seen, only 50mm was left between the baffle door and the expansion joint. As a result, when the baffle door was opened, the deflector was directly ruined. So how do you set the distance?
- The baffle door is in front of the expansion joint (near the heat source side):Leave a straight pipe section of at least 200mm in the middle to allow the airflow to be stable. When the blade of the baffle door moves, it is not necessary to consider the displacement of the expansion joint, but it should be careful that the guide tube cannot extend into the interior of the baffle door.
- The baffle door is behind the expansion joint (near the cold source side):Leave at least 150mm in the middle, and verify that the maximum compression of the expansion joint will not pull the baffle door askew. If you are usingElectric plug-in insulation door, its plug-in board stroke is long, and the distance is best increased to more than 250mm.
The minimum clear distance between the expansion joint and the baffle door shall not be less than 0.3 times the diameter of the expansion joint. For example, the diameter is 800mm, and the distance is 240mm. It's better to be big than small.
Step 4: The length of the guide tube is neglected, and the installation distance is completely wasted
This step is the easiest to turn a deaf ear to. Many people think that the deflector is just a liner? It doesn't matter how long or less. Big mistake.
expansion joint guide tubeThe function is to guide the smoke smoothly through the bellows and prevent the high-speed airflow from impacting the corrugated root. If the guide tube is too short, the airflow directly washes away the ripples, which can be worn out in half a year; If the deflector is too long, it sticks inside adjacent equipment (such as a baffle door or reducer), and the installation distance in that location will be eaten up.
For example, you originally calculated that the flange spacing on both sides of the expansion joint was 1200mm, but as a result, the guide tube extended by 100mm more, and it directly pushed against the bolt of the opposite flange. How do you tighten it?
The length of the guide tube is generally 50~100mm shorter than the total length of the expansion joint, depending on the wavenumber and design displacement of your bellows. Before you place an order, you must confirm the extension length of the guide tube with the manufacturer, and ask: "How much allowance is left on both sides of the guide tube?" If you are not at ease, you can ask the manufacturer to provideThe specific function of the guide tubeDescription and dimension drawings.
Measured lesson: If the distance is not calculated correctly, it will leak in half a year. Do you think it will be a loss?
Finally, let's tell the truth. Last year, a cement plant project, the flue was 30 meters long, and six were usedCorrugated expansion joint for power station industry。 The installation team is too troublesome, the fixed bracket is not close to the expansion joint, and the distance between the guide brackets is pulled to 3 meters. As a result, as soon as the boiler was opened, after the pipeline expanded, the middle section directly pushed to the steel structure, and the expansion joint was pulled out of the crack. After half a year, the furnace was stopped by gas leakage.
Rework? First, the deformed flue was cut off, the bracket was rearranged, and then the expansion joint was replaced with a new one. It cost 150,000 before and after. At the beginning, if you pressFlue expansion joint distance requirementsTo arrange, it will take up to two days of labor. Which do you say is a good deal?
So, don't try to save trouble. If you are unsure, directly turn to the national standard (such as JB/T 12235-2015, the national standard for non-metallic expansion joints), or call the manufacturer's technology. These products in our site- -Metal rectangular expansion joint、Rectangular non-metallic expansion joint、Flue gas baffle door— — There are corresponding guidance. If you don't understand, ask, which is better than rework.