If you are impact testing per AWS D1.1, ASME Section VIII has no relavence whatsoever. All I have handy is AWS D1.1:2002, where the CVN table in annex III calls for a 20F reduction in temp for a 10x5mm specimen. So those proposing the -30F are correct assuming the table hasn't changed in the 2006 edition, or whichever edition you are working to.