Why is the end structure of the compensator more critical than the corrugated body?
Two days ago, a customer who was doing a flue gas desulfurization project came over, and the pipeline wasDesulfurization flue gas baffle doorAndNon-metallic expansion jointAs a result, the end flange gasket was selected wrong, and it leaked in less than two months. You say it was wrong or not? The end of the compensator is the "joint" of stress transmission in the pipeline system, which not only has to bear the medium pressure and temperature displacement, but also has to bear the on-site installation error-if the workers are slightly misaligned, the end has to be carried hard. Once there is a problem with the end structure, no matter how good the bellows is, it will be for nothing. So don't just stare at the number of ripples, the end design is the "one-vote veto" link.
There are only a few common end structures, but the selection doorway is very deep
Most commonlyFlanged connection, applicable to mostUniversal corrugated expansion jointAndMetal hose。 Here's the pit: flange standards (HG/T, GB, ANSI) must match the pipe. Some people try to save trouble. When they buy it, they find that the flange bolt holes don't match. Expanding or repairing welding on the spot is equivalent to digging a hole for themselves. Once the sealing surface is deformed, it will be a matter of time before it leaks.
welded endCommonly used in high temperature and high pressure applications, such asCorrugated expansion joint for power station industryAndHigh temperature axial expansion joint, direct butt welding with pipeline, high strength but not detachable, can only be cut during maintenance. This structure requires extremely high welders' skills, and the weld flaw detection fails? Then you might as well use a flange.
AndThreaded connection, mostly used for small caliberrubber compensatorOrSpecial hose for vacuum。 But don't use threads for large-diameter pipes-the torque control is not good, and the ends are cracked directly. I have seen the rubber compensator of DN300, and the threaded ends are cracked like spiderwebs. Therefore, the thread is only suitable for small diameter and low pressure occasions.
The cooperation between the end and the guide tube is a detail that many people ignore
The inside of the end of the expansion joint is usually addedguide tube(The role of the guide tube is specifically talked about in the question and answer of this site), and its core task is to guide the flow direction of the medium and protect the bellows from erosion. But how to fix the end of the guide tube? Is it welded to the end tube or is it a sliding fit?
RightDirect buried (fully buried) type expansion jointAndExternal pressure single axial expansion jointFor example, the guide tube must be integrated with the end structure. Otherwise, when the guide tube is displaced during thermal expansion, the bellows will be scratched, and the scratch is the stress concentration point, and the fatigue life will be directly folded in half. And guess what? Some customers remove the guide tube in order to save costs, and as a result, the medium directly impacts the root of the bellows, which is perforated in one year. Is it a good deal to save hundreds of dollars and lose tens of thousands?
Under different working conditions, the design difference of end structure can be ridiculously large
Such asPTFE-lined hoseThe end must be flanged and coated, otherwise there will be gaps between the PTFE lining and the metal end tube, and the corrosive medium will bulge when it seeps in. What should I do if I bulge? You can only change the whole root. Another exampleRectangular non-metallic expansion jointThe end portion is a frame structure, and the fabric fibers are fixed by beads and bolts. Here, the bolt hole spacing design should be accurate. If you screw it too tightly, you will crush the fiber and loosen the air leakage. I have seen a steel mill project where the bolt spacing was 50mm larger, and as a result the fibers were clattered by the wind and worn out in three months.
AndRotary compensatorThe end is actually a rotary seal structure, using high-temperature-resistant graphite packing, which is completely different from our conventional welded end. The compression amount and replacement space of the packing must be considered in the design, otherwise the torque will be large and the seal will fail.
Several typical scenarios of end failure, how many have you encountered?
The first type：Large diameter thick wall expansion jointCracked end weld. It is mostly because the thrust of the pipe system is not calculated clearly, and the weld bears extra bending moment. When designing, only the axial thrust is calculated, and the lateral wind load and earthquake load are forgotten. It is strange that the weld does not crack.
The second type：Compound hinge transverse expansion jointThe end bolts are loose and the hinge plate is displaced causing the end tube to jam. This kind of problem often lies in the vibration condition, the bolts are loosened when they vibrate without anti-loosening washers.
The third most injustice：Manual plug-in insulation doorAndElectric plug-in insulation doorThe end interface, because there is not enough operating space during installation, the board can't be pulled out during later maintenance. In the design stage, the installation space and maintenance channel must be taken into account. Don't wait until the wrench can't be stuffed in.
Here is a practical suggestion: The end structure design must be combined with product model and standard
Don't think about taking a generic scheme for all projects. For example, if you chooseCurved tube pressure balance expansion jointThe end is to bear the weight of the pressure thrust balancing mechanism; chooseDouble hinge expansion joint for air-cooled island vacuum pipelineHow much Pa does the end seal structure have to vacuum? These parameters have to be determined at the drawing stage. From the product list of this siteRubber PTFE compensatorToSleeve type pipe expansion jointEach kind of end design has particular attention. Rework when something goes wrong? That cost is more than doubled-construction delays and losses from production stoppages are enough to buy several sets of equipment.
Therefore, the next time you design a compensator, first think clearly how to connect the ends. If the connection method is not selected correctly, the rest will be all in vain. It's as simple as that.