Step 1: Find out the temper of the flue-temperature, pressure and medium can't be missed
Alas, the most afraid thing about choosing expansion joints is to pat your forehead when you come up. You have to first figure out the "temper" of the flue-that is, its operating parameters. Temperature, pressure, and medium are all three.
For temperature, don't just look at the design value, but also the actual operating peak. The flue temperature of some power plants can soar above 200℃, and ordinary rubber can't bear it at all, so you have to consider the high-temperature resistant rubber compensator, or directly put on the non-metallic expansion joint (fabric fiber expansion joint). What about the stress? Positive or negative pressure? If the negative pressure pipeline chooses an expansion joint that is too rigid, it will deflate directly. Do you think it is bad?
The medium is more realistic. Sulfur in flue gas? Got dust? How corrosive is it? Two days ago, I met a customer. The concentration of sulfur dioxide in the flue was high, and the ordinary rubber rotted in a month. Finally, the rubber PTFE compensator was changed to stabilize. Therefore, listing the working condition parameters clearly is the first and most important step in the selection.
Step 2: Check it in – rubber compensator or non-metallic expansion joint? Don't choose the wrong one
You already have parameters in your hand at this time, but don't rush to place an order. You have to figure out: Should you use a rubber compensator, or a non-metallic expansion joint?
To put it simply and crudely – rubber compensators are more flexible if the space is tight and you need to absorb multi-directional displacement; If the temperature is high (more than 250 °C), or the flue diameter is large (for example, more than 2 meters), then non-metallic expansion joints (fabric fiber expansion joints) are a more reliable choice. It is not afraid of high temperatures, it can also absorb various displacements in axial, transverse and angular directions, and it is lightweight and easy to install.
But be aware, don't forget that there is also something called "rectangular non-metallic expansion joint", which is specifically used on square flues. Don't choose the wrong shape, or the flanges won't even match. If you are not sure, you can send the drawings and we will help you consult.
Step 3: Tailoring-How to determine flange size, compensation amount and installation space
Okay, the type is set, the next step is the size. It's like making clothes. If you don't measure them correctly, you can't put them on.
Don't only report "DN600" for flange size, but check the actual hole spacing, the number of bolts and the form of sealing surface. The marks on some engineering drawings are quite different from the physical objects on the spot, so it is best to measure them on the spot with a caliper. What about the amount of compensation? This depends on the thermal expansion calculation of the pipe. Don't be greedy for more-the compensation amount is too large, and the expansion joint is easy to fatigue; Don't save it-if you leave less, you will lose a lot if the pipeline stress breaks the equipment.
Many people ignore the installation space. The expansion joint is not a straight tube, it has to have the margin to expand, contract and swing. For example, the rubber compensator needs to reserve the operation space for flange butting, and the non-metallic expansion joint must ensure that the fabric layer does not rub the structural beam next to it. Measure it in advance. Don't install it halfway and find that it can't fit in. It will be embarrassing.
Step 4: Before hands-on installation-these details are not paid attention to, and the air will leak after installation
When things are in hand, the installation stage is the easiest to go wrong. And guess what? Ten air leakage sites, eight are installation problems.
First, the flange face must be cleaned up. Slag, rust and raised welds are all smoothed. The sealing surfaces of rubber compensators or non-metallic expansion joints are very delicate, and a little burr can break them. Secondly, the bolts should be twisted symmetrically, pre-tightened two to three times, and don't screw to death once. Screw diagonally in sequence, otherwise the flange will be unevenly stressed, and air leakage will be a matter of time.
Also, do not install the direction of the guide tube backwards. The direction of the arrow of the expansion joint refers to the flow direction of the medium. If it is dressed in reverse, the guide tube becomes a baffle, and the airflow impact directly hits the expansion joint body, thus reducing its life. If you can't find the arrow, look at the structure-usually the bell mouth is facing the medium.
Remember to remove the screw for installing temporary support! When the expansion joint leaves the factory, the tie rod or screw is used for transportation and fixation. If it is not disassembled, the expansion joint will not work properly. If you see that the bolt is still screwed, loosen it.
Step 5: Routine Maintenance – How Often to Check? How to replace it if it is broken?
Don't think you'll be all right when you install it. The flue expansion joint works in high temperature, dust and corrosion environment every day, and regular inspection can avoid unplanned shutdown.
See whether there are cracks and bulges on the rubber surface, and whether the non-metallic fabric is out of line and worn. Do a full inspection every year, including whether the flange bolts are loose and whether the compensation amount is within the allowable range. If you find leakage, don't panic-small cracks can be temporarily treated with special repair glue, but if it is a large area of aging or perforation, it is safer to replace it with a new one directly.
When changing, stop the machine to relieve pressure first, mark the flange position before dismantling the old parts, and refer to the installation process of Step 4 when installing new parts.
Reserve one or two spare parts when selecting, especially non-metallic expansion joints, whose fabric layer is consumable. Keep spare parts, so you don't have to scratch blind at critical moments.