I hope this information will help find the right solution:
When a heat exchanger has a flow-induced vibration problem, some corrective actions are available to reduce or eliminate the problem. First, verify that the vibration arises from shellside flow, not from some other external source. After you ascertain that the vibration is flow-induced, consider the following actions:
i Plug leaking tubes Often, one of the first indications of a tube vibration problem is that some of the tubes are leaking. The expedient response is to plug the leaking tubes and/or to weld the seal in place. Replacing tubes in the field is generally not practical. While this solution does not address the problem of flow-induced vibration, it can permit continued operation of the heat exchanger until the next maintenance turnaround.
i Remove tubes to create bypass lanes For a heat exchanger with a tube vibration problem caused by fluidelastic instability, creating artificial bypass lanes in the window area is an effective temporary remedy. First, remove tubes in the window areas to create a lane from the baffle tip to the shell parallel to the direction of flow. Then plug the tube sheet where tubes were removed. Allow additional bypassing; do not seal the holes in the baffles. This temporary solution, which lowers shellside pressure drop and reduces shellside thermal performance, is particularly attractive when the heat exchanger is tubeside heat transfer limited.
i Reduce shellside flow rate Because flow-induced vibration depends strongly upon velocity, reducing the shellside flow rate temporarily minimizes the vibration problem. This solution is acceptable only if the reduction can be tolerated within plant operating requirements.
i Stiffen the bundle Increase natural frequencies of an existing tube bundle by inserting lacing or driving wedges between tubes, thus restricting tube motion and preventing wear. Lacing and wedging are often used in the U-bend of U-tube bundles, which can be particularly susceptible to tube vibration problems. Thermal and pressure drop performance can be significantly altered, depending upon the way bundle stiffening is accomplished.
i Roll tubes in baffles near nozzles Rolling tubes in the region where they penetrate baffles is a tricky and expensive operation. However, it has successfully eliminated tube vibration problems originating from nozzle flow in end zones.
i Add deresonating baffles When the problem is acoustic vibration, pull the bundle, remove selected tubes, and add deresonating baffles. If resonant frequency measurements have been made, the deresonating baffles can be positioned precisely to correct the problem. Loss of tubes somewhat reduces thermal performance of the heat exchanger.
i Remove tubes to control acoustic vibration Another approach is selective removal of tubes from the bundle. Measure acoustic vibration characteristics of the heat exchanger before designing the solution. The tubes to be removed depend upon the bundle’s geometric arrangement. This approach has been particularly successful with double-segmental baffled heat exchangers where tubes have been removed in the tube overlap region. Because the number of tubes removed is small, the loss in thermal performance is small.
i Replace tube bundle At times, the only solution to a flow-induced vibration problem is to redesign and install a new bundle. Because maintaining the same shell and external piping is often desirable, the design configuration is limited to the existing envelope; however, considerably different internal features can be involved. If the replacement bundle is to use a different tube material and/or baffle arrangement, performing a vibration analysis ensures no new vibration problem
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