Please help! convert from surface model to solid model

Hi,

I normally get "closed surface" iges file or step file. (see attached)

Both are same model, but different format.

I just don't know which is better format.

I'd like to convert closed-surface model to solid model,

Would you let me know how to?

(I'v tried with iges file using surf-sculpt, but it says it is not watertight model

If so, How can I close the gap?)

and after converting, how can I check the model type (surface? or solid?)

I am using AutoCAD 2013 student version.

Thank you!

Test2.zip

I can convert it to several separate solids but I can't union it because there are inconsistencies in the geometry which are quite evident if one zooms in for a closer look at the various sections.

Why not redraw it in AutoCAD since it really just appears to be an extruded circle?

Would you please please try with this file again?

newsurf.zip

If this doesn't work, I will try re-model in Auto cad.

Unfortunately I can't do it at this time as I am not on my CAD computer. Perhaps someone else might be able to assist you.

I tried using CONVTOSOLID and also SURFSCULPT. Both operations failed.

As ReMark mentioned, there are some obvious errors with your geometry. Switch to Conceptual Display and zoom in on the ends of the tube. You need to fix these problems or redraw by extruding a circle along a Polyline path. Personally, I think redrawing would be much easier and faster than trying to fix the problem.