Size of Openings in Skirt

[TheEverest]

Dear all,
Can anyone help me decide the nominal hole size for a skirt access in a skirt of height 4'-0"?

 

[r6155]

Opening in skirt may be circular, oval, etc.

“See Pressure Vessel Design Manual”, by D. Moss and “Presuure Vessel Design Handbook”, by Bednar

Also as Tailing Trunnion:
Utilizes reinforced openings in skirt with through pipe. Pipe is removed after erection and the openings used as
skirt manways.

Regards