torsani,
The Manway is a nozzle, perhaps less stressed than a process nozzle connected to the plant piping. That is, the UG-45 applies in full for the sizing of the Manway nozzle neck thickness.
cheers,
gr2vessels
gents,
The design of a manway could be simple or complex, therefore the various sub-clauses of UG-45 may apply selectively or in full. It is not unusual to lift the vertical vessel by the lugs welded to the top manway cover, as well as inserting a pressure relief nozzle / valve on the manway cover, including some piping with their own loads, affecting the design of the manway. Sometimes, you hang a few internals to the manway cover also, hence the manway design turns into a ordinary nozzle design.
cheers,
gr2vessels