Welcome to the forum HD
Yes,
Get an engineer with super alloy experience involved.
Not really being a smart alec... Just the best advice there is.
Inconel is a family of literally dozens of base and filler metals... It's not just one alloy... Also are the temps you describe the temps that will be found in joining the metals or in service after the welds, you were unclear.
You may have municipal or code considerations, procedure qualifications, welder quals etc that may need to also be addressed.
There is absolutly no way your question can be answered with the information given, and even then you would be recieving engineering level advice from a welding chat room... Which is nice, but not solid enough to move forward with.
So tell us more, we will tell you more, and then please also get a professional involved and pay them for signatures in the right places. :)
Hi
I am with Lawrence on this one. This question can only be answered by an engineer doing the right calcs, with the right information. The design engineers do these types of calcs the whole time, so it is not rocket science. (Maybe it IS rocket science, but not difficult rocket science:-)
Regards
Niekie