Hello John,
I propose you the following procedure (this can be applied by using Advance Steel on the top of a recent release of AutoCAD (e.g. AutoCAD 2012)) :
- Create the desired tube in your 3D model
- Select the tube, make a right-click and choose "Explode to ACIS" => the tube is now a 3D solid
- Select the obtained 3D solid , then go in the "Plug-ins" ribbon, then press "Edit in fusion" icon => Autodesk Inventor Fusion opens with the selected 3D solid
- Go to File > Save as => in the "Type" combobox, you will find the different possibilities such as Parasolid files, IGES files ... (see attached picture)
Let me know if it helps you
Best regards
Philippe
Attachment: Save as possibilities from Autodesk Inventor Fusion.png