Esteemed experts,
please, which is the centerline nozzle height I have to consider in nozzle flexibility if API 650 tank has double bottom?

Is it height measured from upper bottom plate or from lower bottom plate?

Thanks

Best regards

The lower bottom will result in a more conservative answer. However, I would be inclined to believe the upper bottom is more accurate, as it is from this reference point that hydrostatic forces will be rotating the wall.

Thanks Mr. Fletcher.