Socket Welding flanges have counter bore is slightly larger than the Outer Diameter of the matching pipe, allowing the pipe to be inserted.

A restriction is built into the bottom of the bore, which acts as a shoulder for the pipe to rest on, and has the same ID of matching pipe.

Since socket-welding connections are not as strong as butt-welded joints, the use of this type of flange is almost always confined to NPS 4 (DN 100) and smaller sizes, and to the lower pressure ratings. Its chief advantage lies in the ease of preparation and installation.