Hi,
I am remodeling a bathroom in the basement and after removing the
toilet, found the flange was very corroded and old. I tried scraping
what I believed was a wax ring away to see where the flange began and
pieces of the flange itself came apart (metal).
The pipe has an interior diameter of about 3.5 inches. It's hard to
tell what type of metal it is but I know another shower drain project
(right next to it) revealed copper drain pipes.

My question is, how difficult is it to replace this flange? Does the
flange have to be sealed to the original pipe via some type of welding
or can I simply use a plastic flange, fit it inside the original and
screw it into the concrete with anchor bolts?

Thanks