Here's one: Conduit Indenter Tool
I'm not sure if this has been mention? you could take the next size smaller pipe cut 6-7" pc slide into one end drill through the part you want to become permanent, then turn pipe 1/4 turn and spot weld the hole closed, then you would have the reduce end to make the connection with to the next pipe, of course then cleanup and taper all ends with a grinder or belt sander,
If you don't need a lot and strength is not a problem you might consider 1/2" copper water pipe. Just use the heavier typle "L" instead of type M