See attached PDF file.
Why is the round duct shown as single line even though the detail level is fine?
Solved! Go to Solution.
Because it is a duct placeholder - as indicated on the tooltip adjacent to your cursor.
Duct placeholders are there to allow you to efectively place the centreline at an early design stage before commiting to double line or having to play around with varying detail levels
These can be converted to 3D ducts by selecting the placeholder and in the contextual tab selecting "Convert Placeholder"