To hold the bundle in place if only the channel needs to be removed, collar bolts are utilised with removable bundle heat exchangers. Collar bolts must be used on at least 25% of the flange studs, or at least four of them. Each and every collar bolt must have a square extension beyond the threads that can be used with a wrench to prevent the bolt from rotating when the nuts are tightened or removed.
For removable bundle heat exchangers, collar bolts are a type of fastener that are frequently used to retain the bundle precisely where it needs to be. This guarantees that the channel will be removed without interfering with or damaging the seal between the tube sheet and the shell.
The primary goal and benefit of the collar bolts is improved maintainability since every time the channel is removed, the bundle must also be removed in order to replace the gasket between the tube sheet and shell, which is necessary to prevent leaks after pressurizing the exchanger. The Mean Time To Repair/Restore (MTTR) increases with the replacement of the bundle gasket.
- There is no requirement to remove the bundle if the channel is removed, according to some field experience. This viewpoint is based on some unique expertise with cam profile gaskets and the application of initial correct tension to achieve the necessary gasket stress.
- The machining and replacement of the bolts in the event that tapped holes are used and the bolts become stuck would take a lot of time and might be beyond the capacity of the maintenance staff.
- In order to prevent the maintenance team from being misled, the collar bolts must be adequately marked or stamped. Otherwise, collar bolts may be mistakenly removed.
- comparatively more expensive as a result of the larger tube sheet size and the drilling work needed for the tube sheet’s bolt holes.
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