RBI 581 - Reynolds number in a vessel for CO2 damage factor

Hi all,

A technical question for applying RBI 581 to a vessel, such as a separator, for calculating the CO2 damage factor.

Part of the damage factor calculation requires the Reynold's number so the friction factor can be calculated. This is easy to calculate for a pipe, but how does one go for a vessel? Do you use the pipe diameter and flow velocity of the inlet? It is not specified in API 581 how to deal with this.

Thanks in advance,
R