Seam to seam length is the total physical length of the separator between the weld seams where the shell mates up with the head at each end of the vessel. The effective length is the actual length where separation of phases actually occurs. For example, you can have a horizontal 3-phase separator that is 20 feet seam to seam, but if you have a weir 15 feet from one end for overflow of separated HC, the effective length is a maximum of 15 feet only because the length after the weir is for HC residence time only and cannot be used for separation. Depending on how the inlet nozzle and mist eliminator are located, they can further reduce the effective length. Hope that is clear.

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