Stainless steel would spall in that location, too, unfortunately. The temp at the top of the heat riser is going to exceed the working temp of any [affordable] metal alloy one could use there. (Inconel or 330 series nickel-stainless might work, but the cost is just *outrageous.*
One thing that might help would be to use high-alumina castable refractory — and coat the inside and outside of the barrel wall in that spot. The spalling itself is a result of oxygen attacking the metal when it’s white-hot…causing those oxidized chips of metal to flake off. In theory, if you can prevent the O2 from contacting the metal, then the spalling would be mitigated.
Edit: I didn’t see the 2nd page button of this thread. My post was meant to reply to Greg’s post at the end of the first page:
Greg Martin wrote:Do you think it would be hard to find a stainless steel inner drum that size? Otherwise, I wonder if an internal stainless steel bent sheet deflector would work to help distribute the heat a little to help eliminate the focused hot spot and avoid the spalling?