One thing you will have to watch out for if you have CVN requirements, is violating the time at temperature the welding procedure is qualified for. As far as a numerical limit, I am not aware of one.

Each welding process has specific requirements that are not the same for each, and PWHT requirements depend on whether impact requirements are imposed by the construction code.

In general, the PWHT used to qualify has to reflect what is done in production. In one case Section IX says the aggragate time must be 80% of the time used in production. Another paragraph states that a separate PQR is needed if there is a change of more than 10% of the post heating cycles following the weld interval. Again, the paragraphs that apply are process specific and do not apply universally to all welding processes.

Good luck - Al