The only difficulty is valve size. The super or conventional duplex stainless steel can be welded to carbon steel using a 309MoL filler metal butter layer on top of the carbon steel substrate followed by the duplex ss or super duplex ss deposited on top of the butter layer.
The 309MoL is needed as the first layer.
The bigger problem will be seeing if the SDSS cools fast enough to have good corrosion properties. You need to take a trial piece that has the same section thickness and see if it will pass an A923 ferric chloride test.
If the structure is so loaded with intermetallics that it has poor corrosion resistance then you would be better off moving to a 6%Mo super-austenitic grade.
I know that the duplex is strong and has good cavitation resistance, but if you can't get the corrosion resistance it will be for naught.
