Whip,
If you are required to use an Inconel product, then ERNiCrMo-3 (625) is the most used. The use of a nickel alloy, personally, concerns me. 2205 Duplex is a nitrogen alloyed material. The nitrogen gives added pitting corrosion resistance and added strength to the material. 625 has a slightly higher PREN (pitting resistance equivalency number) than the 2205, but the 625 also contains niobium. Now, niobium has a high affinity for the nitrogen in the 2205, and will deplete the nitrogen in the HTHAZ and will result in high ferritic zones and loss of corrosion protection and toughness. So, what is more important, a slightly higher corrosion resistance on the weld bead ONLY, or the loss of corrosion resistance and toughness in the HAZ? If there are going to be any problems in this type of weld, it is going to be in the HAZ, not the weld bead of 625. Personally, even though I have seen 625 specified to weld 2205 Duplex, I feel that the niobium in the 625 will have greater negative effects that if the correct filler metal (ER2209) for a 2205 was used. But, if that is what your contract specifies, then you must use it.