This is up to the owner to decide, nothing is defined by the standard.
In my opinion the repair of a leaking weld in a main run or the addition of drains with relatively large diameter would be major changes, whereas the insertion of a threadolet for a small drain or vent, if properly ND tested and assuming no PWHT requirements apply, could be considered a minor change.
prex
motori@xcalcsREMOVE.com
