If you review Appendix A-1 in B31.3, the minimum design temperature is -325 deg F. Now review Table 323.2.2 and for austenitic stainless steels look at row 4 column 4a for guidance and notes.
(f) Impact testing is not required for the following
combinations of weld metals and design minimum
temperatures:
(1) for austenitic stainless steel base materials having
a carbon content not exceeding 0.10%, welded without
filler metal, at design minimum temperatures of
−101°C (−150°F) and higher
(2) for austenitic weld metal
(-a) having a carbon content not exceeding 0.10%,
and produced with filler metals conforming to
AWS A5.4, A5.9, A5.11, A5.14, or A5.221 at design minimum
temperatures of −101°C (−150°F) and higher, or
(-b) having a carbon content exceeding 0.10%,
and produced with filler metals conforming to...
so, look at (f) 2 above and check the notes.