A Weldolet is a butt-weld branch connection. It is designed to provide integral reinforcement and minimize stress. They are made to match or exceed the schedule of the pipe.
wildly welding main pipe the are fillet weld or butweld
To be fully welded out plus a fillet of @ 6mm to reduce the stress concentration factor at the bottom toe.
There are size on size weldolets. The hold on the run pipe will necessarily be undersize (either hot tap or torch ) because it's not possible to cut the same size hole in the run without damaging the base material.
Weldolet is a trademarked name by Bonney Forge for internally reinforced forged branch outlet fittings. Pipet is a trademarked name by WFI for internally reinforced forged branch outlet fittings. Both comply with MSS SP-97 Internally Reinforced Forged Branch Outlet Fittings - Socket Welding, Threaded and Buttwelding Ends. Referenced in ASME B31.3-2020 304.3.1 a) (1). They are the same
Weldolet and Sockolet are basically self reinforced fittings. Weldolet is used for Butt weld branch connection where standard tee is not available due to size restrictions and the piping is of critical / high pressure service. Sockolet is used for socket welding branch connection, which require reinforcing pad.