I apologize for being so long in posting a response, I've been out of pocket in the Rockies.
It appears that you are asking about a studded connection, which may be installed as a pad or as a studded outlet into the vessel shell, or head. Section VIII, Div.1 addresses this item in UG-43 (a), (b), and (d) Studded Connections. You must design the connection reinforcement using the calculations found in UG-36 thru UG-42 as you would with any other opening in the shell or head. I trust this data is satisfactory for your need.