First, find out what "too long" is all about-common cause investigation
Many people ask as soon as they come up, "What should I do if the metal expansion joint is too long?", but we have to first see whether this "too long" is not calculated correctly by design, or it is forced in during installation. There are three common reasons: First, the thermal elongation of the pipeline is considered large during design and selection, or the cold tightness is not considered at all; Second, there is a deviation between the actual center distance of the on-site pipeline and the drawing, such as support settlement and flange misalignment; Third, the factory length of the expansion joint itself is too large-for example, you ordered a general-purpose corrugated expansion joint, but the supplier delivered it according to the standard length, and did not customize and shorten it. Two days ago, a customer of a power plant took an external pressure single axial expansion joint. The actual installation space was only 300mm, but the one he bought was 400mm long. Do you think this can be installed?
Second, don't hurry to cut, try "adjust the installation position" and "change the bracket" first
The expansion joint is too long, and it is not the only way to cut. In many cases, adjusting the pipe bracket or adding a bias can solve the problem. For example, if your pipe has installation allowance, you can retract the fixing bracket a little, so that the connectors at both ends of the expansion joint extend more into the pipe. Alternatively, if the expansion joint has a tie rod nut (like a large tie rod expansion joint), try loosening the nut to allow the bellows to compress-be careful not to exceed the allowable amount of compression. Don't forget what the expansion joint guide does: it both protects the bellows and limits excessive compression. If you use a double hinge transverse expansion joint, it itself can absorb angular displacement through the hinge, and a slight adjustment of the angle can "eat" part of the length. If it doesn't work, you can add a short section to the pipe to fill up the space.
3. Wrong selection? Then switch to an expansion joint construction-recommended alternative
If the installation and adjustment can't be done, the problem is probably in the selection. At this time, it is necessary to change a more suitable model according to the pipeline displacement, pressure, temperature and other parameters. For example: you originally used a general-purpose corrugated expansion joint, but thought it was too long, so you can replace it with a straight tube pressure balanced expansion joint or a double straight tube bypass pressure balanced expansion joint, which is more compact in structure and has a shorter axial length. If it is a high-temperature steam pipeline, consider the high-temperature axial expansion joint, which has less corrugations, large stiffness and shorter length under the same compensation amount. There is also an extreme practice: instead of the axial expansion joint, the rotary compensator is a sleeve-type structure with a fixed length and is not affected by bellows compensation. Note, however, that rotary compensators are not suitable for high-pressure applications. Here is a reminder that you must check the pipeline thrust before changing the model, otherwise it is easy to pull the bracket.
4. The last way: Cut or return to the factory-but the risks must be clear
Some old masters say, "Saw off a piece of isn't it over?" Don't do this! Each wave of the bellows of the metal expansion joint is calculated according to the design pressure, and cutting will destroy the end structure and stress distribution, which directly leads to the instability or leakage of the bellows. Only a few circumstances are possible: if the manufacturer reserves a cut allowance and you have accurate welding process documentation on hand, you can short-circuit it-for example, large-diameter thick-walled expansion joints sometimes leave a straight edge section on the end tube, allowing you to cut off the excess and re-weld the joint. However, in most cases, it is recommended to contact the manufacturer directly to return to the factory for modification, or change to a customized length. For example, the directly buried (fully buried) expansion joint of this station is made according to the measured length of the construction site after leaving the factory, so there is no problem of being too long at all. Remember: cutting the bellows is equal to scrapping, and cutting the end pipe should also ensure the welding quality. Don't save small money and suffer big losses.
5. How to avoid "too long" from the beginning-3 key points in the design selection stage
Instead of remediating afterwards, it is better to get stuck in the front. First, when calculating the thermal elongation of the pipeline, it should be calculated according to the difference between the actual working temperature and the installation temperature, and don't leave too much margin; Second, preference is given to the type of expansion joint with compact structure-for example, in the pipe gallery with limited space, the double hinge transverse expansion joint or the curved pipe pressure balance expansion joint is much shorter than the single axial type; Third, before ordering, let the manufacturer produce according to the measured size on the spot, or mark the cold tightness on the installation drawing. For example, the corrugated expansion joints for power station industry and metal corrugated expansion joints for cement industry in this station all support non-standard customized length according to working conditions. In addition, don't ignore the non-metallic expansion joint (fabric fiber expansion joint), which occupies little space and is light in weight, and can replace the metal expansion joint under some working conditions.