Robotic welders are limited in what they can do, but what they do, they do well! (mindless repetive jobs!)
I watched one do it's thing in one shop and it was quite a neat thing to witness. They are limited though, pretty much to the consistency of a parts fit up, the programmer and what the part is. Smaller parts in batches of 2000 where all of the pieces are the same and the fit is the same everytime, they work great! Not so much for anything else, as they cannot currently see the puddle and are limited in their range of motion, although a lot of them still require an operator.
I would say that erection, heavy fab and custom work is pretty safe for quite awhile yet!
One of the neater machines to watch cycle is a turret punch. I had to run one for awhile at one shop and I was thinking to myself, "The guy that came up with this thing was either a genious or manically insane!"