How to choose and install flue expansion joint of power plant boiler? Follow these steps and make no mistake

Step 1: Figure out exactly what kind of expansion joint you need for your flue first – metal or non-metal?

Alas, this matter is actually a place where many people stumble. As soon as I arrived at the scene, I was stunned: metal? Non-metallic? I will use what others use? Don't do that.

The working conditions in the boiler flue are quite special-the temperature is generally only two or three hundred degrees, but there are sulfur, water vapor and sometimes corrosive particles in the flue gas. And guess what? In this case,Non-metallic expansion joints (fabric fiber expansion joints) are instead the more common choice. Why? Because of corrosion resistance, good vibration isolation, easy installation, the cost is much lower than that of metal. This site hasRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)Specially prepared for flue.

However, if the flue temperature exceeds 400℃, or it needs to bear a large pressure (such as the inlet of the desulfurization tower), it has to be metal. LikeCorrugated expansion joint for power station industry、High temperature axial expansion jointOrUniversal corrugated expansion jointAll of them do this job. Metal can carry high temperature and high pressure, but it is afraid of chloride ion corrosion, so you have to be careful when selecting materials.

Tips:Really unsure? Look directly at the flue material and design temperature. Temperature 400 °C, pressure> 0.1 MPa → metal. Don't ask me what to do at 350~400℃-it has to be discussed in detail according to the specific displacement and corrosiveness. I suggest you send the parameters directly to the manufacturer.

Step 2: Measure the displacement, temperature and pressure to determine the model and size

This step is the easiest to overlook, and many people think "just make a rough estimate". As a result, less than half a year after installation, the expansion joint was torn, the pipeline was cracked, and the maintenance cost was more expensive than the equipment itself.

Amount of displacement (axial, transverse, angular), design temperature, design pressure。 How to calculate the displacement amount? Simply put, it is how far the pipeline can run by thermal expansion and contraction. For example, the length of the flue is 10 meters, the temperature rises from normal temperature to 300℃, and the linear expansion coefficient of steel is about 0.012mm/m·℃, so the axial displacement is 10×0.012× (300-20) =33.6mm. After calculation, consider the turns and brackets on the pipeline path, and estimate the lateral and angular displacements.

With these data, you can choose the model. Such asMetal rectangular expansion jointThe size of the flue is generally determined according to the size of the flue interface, but the wave number should be calculated according to the displacement. This site'sModel and size of expansion jointThere is a standard parameter table in the question and answer, so you can check it directly. Don't slap your head with pressure-test pressure by multiplying the design pressure by 1.25 times. Pressure is safer.

Note: If the diameter of your flue is more than 1 meter, do not use the general type.Large diameter thick wall expansion jointOrStraight pipe pressure balanced expansion jointOtherwise, the structural stiffness is not sufficient.

Step 3: Preparation and critical operations before installation (pull rod, guide tube, arrow direction)

Don't rush up when the goods arrive. First, check whether there is any bump in the appearance, whether the ripples are deformed, and check whether the model on the nameplate is ordered by you. Clean the flange sealing surface and align the bolt holes.

• Tie rods: Most expansion joints will be equipped with transport tie rods when they leave the factory to prevent them from being crushed or stretched during transportation. Before installation, adjust the tie rod nut according to the amount of pre-tension (or pre-compression) required by the design. How exactly to adjust? Look at this siteHow to adjust the tie rod nut of expansion jointQ&A – Usually loosen the locking nut first, then rotate the adjustment nut and lock it when it is in place. Note: If it is a working tie rod (such asRotary compensatorOrLarge tie rod expansion joint), cannot be disassembled after installation, must leave the limit.
• Guide tube: There is a guide tube inside the flue expansion joint of many power plant boilers. Its function is to let the flue gas flow smoothly and reduce the erosion of ripples by vortex. The direction of the guide opening must follow the direction of the media flow during installation-that is, the direction of the arrow. The expansion joint housing you buy will usually be marked with an arrow. Remember: the arrow points in the direction of the flue flow.
• Arrow Direction: Don't underestimate this arrow. Non-metallic expansion joints also have directional requirements, especially those with inner lining, which can lead to premature damage to the inner lining when installed backwards. The question and answer of this site "What is the direction of the arrow of the expansion joint" makes it clear that it indicates the flow direction of the medium.

Practical operation: First, hoist the expansion joint in place, and the bolts are attached but not screwed to death. Adjust the position to ensure that the guide tube is centered, and then gradually tighten the bolts diagonally with uniform torque.

Step 4: Check the key points after the installation is completed (don't try it in a hurry)

After installing the expansion joint, someone immediately ignited and tested the machine. As a result, air leakage and deformation were found within two days. Don't worry, do three things first:

1. Check the tie rod: confirm whether the transport tie rod is removed or not? If it is a limit pull rod, is it adjusted in place? Remember that the working rod cannot be removed, but the locking nut must be loosened half to one turn, otherwise the expansion joint will not be able to expand and contract freely.
2. Check the guide tube and seal: Shine it with a flashlight. Is the guide tube offset or stuck? Is the flange gasket extruded? Are the bolts loose? Do it once if you have the conditionHydraulic testOrAirtightness test, of this siteSpecific Function of Expansion Joint Guide TubeAs mentioned in the question and answer, the guide tube also plays the role of protecting the ripples, and if it is installed crooked, it is equivalent to white.
3. Check brackets: Are the fixed brackets and guide brackets near the expansion joint installed in place? Can the pipe move freely within the allowable range? Never subject the expansion joint to improper torsional forces.

All qualified before turning on. Run at low temperature for a while, and then raise to the design temperature after the system is stable, and observe whether there is any abnormal noise or leakage in the expansion joint.

Step 5: Routine maintenance and common troubleshooting (such as what to do about leakage and deformation)

The expansion joint is not a thing that can be installed once and for all. Daily inspection should focus on:

• Leaks: Most commonly flange gasket failure, or aging of non-metallic expansion joints. If leakage is found, tighten the flange bolt first. If it fails, replace the gasket or expansion joint body. This site hasNational standard for non-metallic expansion joints (JB/T 12235-2015), pay attention to the standard selection when replacing.
• Deformation: If the bellows is found to be bulging and twisted, there is a high probability that the displacement exceeds the limit or the bending moment is pulled during installation. At this time, you have to stop the machine to check whether the nearby bracket is crooked and recalibrate it. For metal expansion joints, it is difficult to repair after deformation, and it is safer to replace them with new ones directly.
• Corrosion: The water vapor in the flue contains sulfur, and the metal bellows is prone to pitting. It is recommended to measure the wall thickness regularly.Corrugated expansion joint for power station industryIt is recommended once a year in the product information. If you find serious thinning, replace it in advance, and don't wait for it to leak before repairing it.
• Life: Generally speaking, it is almost time for non-metallic expansion joints to be replaced after 3~5 years, while metal joints can be used for 8~10 years, but they will be shortened in high temperature and high pressure occasions. The Q&A "Service Life of Expansion Joint" of this site mentioned that the life is directly linked to the number of cycles, and special attention should be paid to boilers that start and stop frequently.

Choose the right, install the right, check the right, and expand energy saving for a long time. Don't try to be cheap, and don't pretend by feeling. Follow these five steps and you won't have major problems with your power plant boiler flue expansion joint.