Alloy 625 weld electrode or filler (ENiCrMo-3 or ERNiCrMo-3) is acceptable. Alloy C-22 (ENiCrMo-10 or ERNiCrMo-10) or C-276 (ENiCrMo-4 or ERNiCrMo-4) may also be used.
Ref.: Guidelines for the Welded Fabrication of Nickel Alloys for Corrosion-Resistant Service, Series No. 11012, 1994. Nickel Development Institute.
You can find a lot of very good, FREE info on welding of nickel-base alloys at: www.nidi.org
Marty