I can not get pipes or ducts to display in a 3D rendering. Other mechanical elements will display such as diffusers, radiant ceiling panels, and VAV boxes.
I have tried to apply material types to duct/pipe sytems but the elements will still not show up in a generated Rendering
this is incredibly frustating.
I am using Revit MEP 2012
I tested in a blank project with ducts made of Marble and pipes made of Grass (image attached).
As a test, copy some the offending Pipes and/or Ducts to a new project and attempt to render them. Also, could you attach a full-screen (to include application buttons at the bottom) of the 3D View you're rendering?