No, Grade 8 bolting is not permissable, violation of material and grade.
Rather you need ASTM A193-B7 or B7M studs with ASTM A194-2H or 2HM heavy hex nuts. The "B7M" and "2HM" alternatives conform to the NACE MR-01-75 specification.
The ANSI B31.3 takes into consideration the stress level of bolting and material under various conditions, not only load and temperature. Therefore Charpy Notch Toughness and SCC issues, which directly relate to material considerations, come into play.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
