Socket-
Weld Flanges has a female socket in which pipe is fitted. Fillet welding is done from outside on the pipe. The socket welding flange is similar to a slip-on flange except it has a bore and a counterbore dimension.
The counterbore is slightly larger than the O.D. of the matching pipe, allowing the pipe to be inserted into the flange similar to a slip-on flange.
The diamter of the smaller bore is the same as the I.D. of the matchine pipe A restriction is built into the bottom of the bore which sets as a shoulder for the pipe to rest on.