I'm on a petrochemical project which happens to produce steam as part of the process as well. This steam is even sold to battery limit but is still not the main application of the plant. There is a steam drum and superheaters in the plant and is point of argument whether should be designed as ASME I or ASME VIII; consequently the piping would get split partially in B31.1 and B31.3 if ASME I was selected.
Does this have to be considered as part of the plant and therefore B31.3 or we should split them for before and after first shut-off valve for B31.1 and B31.3 spec break, stress analysis, etc.?
(By the way client has no obligation for either way)

Any thoughts?