1. Selection and preparation before installation: Don't make a mistake in the type of expansion joint
How complex are the flue conditions in power plants? High-temperature flue gas is always five or six hundred degrees, and there are corrosive media in the desulfurization section. The displacement of the pipeline is so large that you can doubt your life. If you choose the wrong model, the back will be completely dry. Square flue preferredMetal rectangular expansion jointBut the ones that can really withstand high temperatures and large displacements must beNon-metallic expansion joint (fabric fiber expansion joint)— — It has high temperature resistance, large compensation, can absorb three-dimensional displacement, and is a frequent visitor of flue system.
If the flue goes through the desulfurization section, you also have to matchDesulfurization flue gas baffle door。 Don't underestimate this step. The baffle door and the expansion joint don't cooperate well, and it is common for air leakage and lax closure. When you get the goods, do three things first: check the product model and displacement parameters, check the direction mark of the guide tube, and confirm the status of the tie rod nut. The deflector arrow must point to the direction of media flow, installed backwards? Just wait for the wear and leak. For details, refer to the Q&A of this site"The direction of the arrow of the expansion joint means"。
2. Key points of installation, positioning and welding: align the pipe nozzle, and don't rush to disassemble the tie rod
What is the most afraid of flue expansion joint installation? Forced counterpart. If the temperature difference or misalignment is pulled up, the stress of the bellows exceeds the standard, and it will crack in no time. Correct approach: First adjust the pipe support so that the expansion joint is in a free length state. When welding, spot welding is positioned first, and then layered welding is used to prevent thermal deformation. Keep one principle in mind – the expansion joint is a flexible compensation, not a pipe correction tool.
Look at the tie rod nut on the expansion joint again, which is for transport protection. Do you want to dismantle it after installation? Depending on the demand: If the expansion joint comes with a limiting function (such asLarge tie rod expansion joint), the tie rod nut must be loosened or removed before the system runs, otherwise the displacement will be limited. How to adjust it specifically? Refer to Q&A on this site"How to adjust the tie rod nut of the expansion joint"。 For large tie rod expansion joints, the length of the tie rod must be adjusted after installation to ensure synchronization on both sides and avoid deflection. And guess what? Some people found it troublesome to weld the nut to death directly. As a result, the expansion joint was scrapped, and the whole set of pipelines suffered.
3. Installation special cases of non-metallic expansion joints: sealing and corrosion protection
Non-metallic expansion joint (fabric fiber expansion joint)It is most used in power plant flues, but it is delicate-the flange face must be cleaned without welding slag or burrs. The sealing gasket should be laid in a whole circle, the bolts should be tightened step by step diagonally, and the torque value should refer to the manufacturer's regulations. Don't use too much force to crush the fabric layer, it won't recover if it is squashed.
In addition, once the outer protective layer of the non-metallic expansion joint (such as fluororubber coating) is damaged, the smoke directly erodes the fiber layer, and the life of the non-metallic expansion joint is sharply reduced. After the installation is completed, do air tightness check, use soapy water or foaming agent to detect leakage, don't be lazy. There is a peer map that saves trouble and does not check for leakage. As a result, it is perforated after three months of operation, and the cost of changing one doubles. Tsk, why bother?
4. Inspection and debugging after installation: displacement verification and bolt tightening
Installed does not mean done. First check that the expansion joint is in the design pre-compressed/pre-stretched state. For example:Corrugated expansion joint for power station industryWhen you leave the factory, you usually pre-stretch 50% of the thermal displacement. You must confirm that the installation direction is correct (the displacement direction is consistent with the expansion joint arrow). Then slowly introduce the medium, and observe whether the expansion and contraction are normal and whether there is any abnormal noise during the heating process. This is when the role of the deflector is evident-it can protect the bellows from high-speed smoke. After installation, confirm that the gap between the guide tube and the inner wall of the pipeline is even, and there is no jamming on both sides. Please refer to the Q&A of this site for specific functions"Specific Function of Expansion Joint Guide Tube"。
Screw all fastening bolts again in the cold state, especially flange bolts and baffle door connecting bolts. It is common sense that it is easy to loosen after hot deformation. Don't believe in "tighten and finish", thermal expansion and contraction will teach you how to be a human being.
5. Common Installation Errors and Remedies
I have been in this business for a long time, and I have seen many pits. Some people install the metal expansion joint in the opposite direction, some people don't leave enough expansion gap, and some people try to save trouble and weld the tie rod limit nut directly to death. What to do in these situations? Install reverse pointing? It has to be removed and reinstalled, there is no other way. Not enough clearance? Check whether the pipe bracket is blocked from sliding-guide bracket and limit bracket should be equipped near the flue expansion joint of the power plant to prevent pipe deviation.Double-sealed single-axis circular baffle doorAnd the expansion joint is improperly matched, for example, if it is not closed tightly, it is necessary to adjust the sealing gap of the door frame and add gaskets if necessary.
The expansion joint is flexible compensation, and the less rigid constraints the better. Never use it to correct pipe installation deviations. Two days ago, I encountered a customer complaining that the expansion joint was leaking. As a result, the pipeline was misaligned and pulled up. What do you think this has to do with the expansion joint? The installation specifications were not followed, but it was quite neat to shake the pot.