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Ya know I haven't been able to duplicate that problem making nearly the same thing. It has something to do with the vertices where the pipe meets the base.

Did you make the pipe separate from the floor base and then weld it? I can tell you that perhaps if you detach and mirror the pipe (or rotate the base) in the other direction and then weld it to the base that probably won't happen when you leave smooth on. I use to have a problem with exporting mirrored objects into Poser. I believe essentially what's happening is Poser is twisting that thing around in it's attempt to smooth it and it's based on the alignment of the vertices. I'm not even sure that adding an edge loop would correct (realigning the vertices) that for smoothing. That's my guess.

 

Since the twisting is occuring closest at the bottom from the base of the pipe.

No, that started off as a plain, flat round cylinder primitive with no height - one round 48 point polygon that I beveled all the way up through all the shapes, past the 90 degree bend, and over. So it was always just one object, never separated, never welded. I deleted that massive ngon at the end too, so that's not the problem.

This was then mirrored too by the way. And yes, I made sure the mirrored points were welded. The image shows only half of it. (It's part of a railing structure). I'll check it out later and see if I can do anything to it to make it work better with smoothing.

An interesting thing to note though. I made what you made in a similar fashion except I started with a flat 4x4 plain. Scaled in the 4 corners, chamfered and opened the center vertex. Then added some edges from the scaled in corners to the center opening. Then built it up from there including the pipe. Then I added a turbosmooth (setting of 2) modifier to the whole thing. Poser rendered that fairly quickly. Another way I did it was starting with a 48 sided cylinder and then making the pipe from a spline with 48 sides converting that to a polygon. Then welded the pipe to the base cylinder.  Took Poser a hell of a lot longer to render that for some reason and I had no intersecting edges in the long open lengths of the pipe with both smooth on and off. Still rendered REALLY slowly. And I didn't get any twisting at render time. I even then added one edge loop. Still slow rendering. Although now that I think about it I didn't turn off smooth in the Render settings. Smooth is in 2 places, the object properties AND the Render settings.

By the way I'm using Max. Poser liked my turbosmoothed mesh more than the 48 sided mesh. The turbosmoothed mesh has slightly less than 48 sides and a higher polygon count. Rendered rather quickly.

Poser is weird man. Definitely. It's a love/hate relationship.