The 2.5 inch pipe I used ended up being 3 inch Outside diameter so fitted the 3 bolt flange. And ended up quashed up.
The 3 inch bends are actually bigger than 3 inch and almost 3.5 inch outside diameter as the size is for the inner diameter when it comes to steam pipe.
Does that make sense?
Here are some close ups of the pipe before weld up.
Might give you some ideas.



Have fun.
Calvin