Ghensky:
The only places you really have to inspect are places that there might be (or there is) a crack. Alternatively, the min. radius might be half the i.d. of the tank or the full girth or length of the weld. You be the judge. Can you make any determination, or engineering judgement, as to what might have caused the crack that you found? Are there any surface indications which look the same, which might be candidates for additional inspection? I’d be surprised that any code would spell something like min. additional distance for an inspection; other than to say a reasonable distance beyond the end of crack to make sure you’ve determined its full extent. They will actually be able to see and determine the full extent of the crack when they start repairing it.