You're going to want to minimize dilution and limit to one pass if possible depending upon the final chemistry required.
You will find with circumferential that the shrinkage will be reduced and more uniform.
Longitudinal overlay has a tendency to shrink more in the middle of the pipe/tube, flare at the ends, and cause ripples depending on substrate thickness (>1/2" should not be noticable).
Longitudinal is easier to visually reference the bead indexing.

If available pulse GMAW is excellent. SAW is more common (better perhaps for something as big as what you have) but of course creates more heat, not to mention that its dilution is higher as well. You can get 6% to 10% without much effort with pulse GMAW. Thats tough with SAW.

Make sure the beads transition as flat as possible. Whether abrasion or corrosion this is important.