The flue expansion joint is misaligned. To put it bluntly, the expansion joint "stands crooked" in the pipeline. The flues of power stations, cement plants and desulfurization systems are often at a high temperature of several hundred degrees. Coupled with wind force and foundation settlement, the expansion joints are prone to axial offset, angular torsion or lateral misalignment. Misalignment is not a trivial matter-from air and smoke leakage to bellows tearing and baffle door jamming. Two days ago, the equipment supervisor of a cement factory complained to me, saying that the non-metallic expansion joint of their factory had been used for less than half a year, and the fabric on one side was bulging, while the other side had already worn holes. When I disassembled it, the misalignment exceeded 30mm, and the guide tube scraped out a deep groove.
How to solve the misalignment of the flue expansion joint? Don't rush to replace it, find out the cause first. I have been in this business for more than ten years, and I have dealt with hundreds of misalignment faults. I have summarized three-step investigation and targeted schemes, which can basically cover more than 90% of the cases.
Step 1: Check the cause, don't let the expansion joint take the blame
First, there is no alignment during installation, and the center line of the pipeline deviates. Civil foundation settlement and support welding deviation, which will be amplified by thermal stress at the initial stage of trial operation. The second is the calculation error of thermal expansion. After the system runs, the actual thermal displacement exceeds the design range. Like power station flue, flue gas temperature fluctuation may reach 200℃, if originally usedHigh temperature axial expansion jointIf the stiffness is selected small, or the wind load is not considered in the selection, misalignment is almost inevitable.
In addition, the flue of cement industry accumulates ash for a long time, and the extra load can "push the expansion joint". Wet flue gas corrosion in desulfurization system causes flange bolts to loosen and also cause displacement. You ask me how to judge? Use laser centering instrument or wire pulling method to measure the offset of the pipeline centerline-if the offset exceeds 20% of the design compensation capacity, it has to be taken seriously.
Check whether the expansion joint tie rod nut is pressed on one side and whether there are any friction marks in the guide tube. If it isNon-metallic expansion joints (fabric fiber expansion joints), look for localized bulging or tearing in the fabric fiber layer – these signs are more convincing than looking crooked to the naked eye. Check it out by the wayFlue gas baffle doorOrRound flapper doorThe opening and closing torque, misalignment often leads to the door panel jamming, the valve is not closed tightly, and the whole maintenance cycle is scrapped. Alas, this detail is overlooked by many people, but one jam may cost you three more days to dismantle the door.
Step 2: Set the level, slight, moderate and severe seats
With the "why" addressed, the next step is "what to do". Everyone who is engaged in industry knows that the same problem can be solved differently under different working conditions. I divided the misalignment into three gears, and you compared them:
Slight misalignment(The offset is within the compensation capacity of the expansion joint, such as 10-15mm): Adjust the tie rod nut, re-tighten evenly, and restore the pre-compression amount. For specific operation, please refer to "How to Adjust the Tie Rod Nut of Expansion Joint" that we talked about before-pay attention to symmetrical screwing, loading multiple times, and not in place at once. After adjustment, run a thermal cycle and re-measure the displacement.
Moderate dislocation(The offset exceeds the compensation capacity by 30% but less than 50%): The light adjustment rod is not enough. Remove the flange and recalibrate the pipe support or foundation. If the pipe support is no longer movable, consider switchingCompound hinge transverse expansion joint-This product can absorb large lateral displacements without generating additional stress, and is especially suitable for renovation projects with limited space. Before, there was a desulfurization tower outlet flue, which was horizontally misaligned by 25mm. After changing the double hinge model, it ran steadily for three years without any problems.
Severe misalignment or repeated misalignmentIn this case, it can be basically concluded that the original design selection is unreasonable. For example, puttingStraight pipe pressure balanced expansion jointInstalled at an elbow that needs to absorb multidirectional displacement, or usedUniversal corrugated expansion jointTo cope with angular displacement (it simply doesn't fit). At this time, it is recommended to change toCurved tube pressure balance expansion jointor increaseRotary compensatorTo release stress. If the flue is rectangular, give priorityMetal rectangular expansion jointOrRectangular non-metallic expansion joint- -Rectangular section has stronger torsion resistance.
If the misalignment causesElectric plug-in insulation doorOrManual plug-in insulation doorStuck, don't break hard-adjust the level of the door frame first, and then consider changing the expansion joint. It's like a chain, and no link can be ignored.
Step 3: Plug the loophole, don't forget to linkage test
Finish troubleshooting, fix, and the last step is verification. Many people finished working after repairing the expansion joint, and as a result, the baffle door was still not closed tightly. And guess what? The misalignment was corrected, but the track of the flapper door itself had been distorted. Therefore, after repairing the expansion joint, it must be linked to testFlue gas baffle doorAndRound Flap Door (Double Seal)The opening and closing moment of. If it isDesulfurization flue gas baffle doorAnd check the sealing surface for corrosion.
In addition, it is recommended to monitor the displacement value once a month during the first three months of operation, and record the temperature and air volume data. Don't be afraid of trouble, these data are the first-hand basis for your next model selection.
Prevention is more cost-effective than remedy after the fact-be sensible
Say a thousand words, how to solve the misalignment of flue expansion joint? The most worry-free way is to avoid it at the source. The selection stage is based on the actual thermal displacement data: the high-temperature sectionHigh temperature axial expansion jointFor desulfurizing wet flue gasrubber compensatorOrRubber PTFE compensator(Good corrosion resistance), for vacuum requirementsSpecial hose for vacuumOrPTFE compensator。 Allow sufficient pre-tension/pre-compression during installation, and monitor the displacement value regularly for three months at the running head. If you can do these things, the probability of misalignment can be reduced by 80%.
By the way, if you're dealing with a misaligned flue expansion joint, or you're not sure which product to use when choosing a model- -Metal hose、PTFE-lined hose、Sleeve type pipe expansion joint、External pressure single axial expansion joint、Large diameter thick wall expansion joint、Double hinge expansion joint for air-cooled island vacuum pipeline、Double-sealed single-axis circular baffle door、Single-axis double-flapper door、Compound straight pipe bypass pressure balanced expansion jointThese are our standing product lines. Remember one principle: Let professional people do professional things, and don't let expansion joints take the blame for you.