Approximately 25%, with a minimum of four, of the flange studs shall be Collar Bolts, in order to keep the bundle in place. All Collar Bolts shall have a square extension beyond the threads for use of a wrench to prevent turning of the bolt when the nuts are tightened or removed.
If only the channel must be removed, it's important that the bundle on the shell side remains fixed. If the bundle comes loose, it is very likely, that the gasket behind the tube sheet will be damaged, so that it is no longer possible, in order to achieve a good seal. As a result, the bundle must still be pulled out, in order to replace the gasket.
Remark(s) of the Author...
Collar Bolts can cause a lot of problems!
Recently I was involved in a Turnaround, where many towers, vessels, reactors, tanks and of course heat exchangers, must be inspected.
What I did't know; most people of the contractors did not know what was a collar bolt.
After install of the channel from E-1x8xB, and after service test no leakage was found.
If no leak is found during service test, generally you can "start-up" the equipment; and that's what happened.
When the operating pressure of the respective heat exchanger was achieved, suddenly there was a substantial leakage.
Not the bundle-channel side, but the bundle-shell side was leak, while only the channel was removed?. Of course I can not make it true, what really went wrong.
My suspicion is:
There are too many, or perhaps all collar bolts, during disassemply of the channel where are removed. As a result, I have already described above.