If the joints will only be rolled I would require one every time.
It must be made to the original specifications, have 'original' tubes installed and then removed, and then the new tubes installed.
How else would you know what rolling torque to use and how tight the joints are?
If you are strength welding people often only do them if they need to qualify the weld procedure (or operator).
If you are seal welding it often comes down to how critical the service is, they are still done regularly.
Ask your re-tubing company what their practice is.
The last - and only - time that a mock up tube to tube sheet joint sample and pull test were mandated by one of my clients was when there was uncertainty regarding the optimization between tube wall thickness reduction and the corresponding mechanical strength of the joint. In this instance, the tubes were 410 stainless steel and the concern was that the vendor's tube rolling procedure in their ITP still proposed 8% to 12% wall reduction as would have been the case with SA-179. Martensitic steel was considered more prone to work hardening, so a mock-up was made of the assembly using surplus materials from the same heats as would be used in fabrication for both the tubes and the tube sheet, and the same tube hole tolerances and grooves. 9 tubes were rolled to various wall thickness reductions and it was shown in the subsequent pull tests that the optimum point in that instance was closer to 5%, which is what was then imposed in the ensuing fabrication.
