A rounded pipe will reduce molecular friction of the fluid or gas traveling in the pipe. Rounded pipes allow freer, faster flow compared with any other shape.
Because that's the easiest way to make them, and the strongest. EDIT: Also the circular shape allows for a smoother flow of liquid within the pipe and less resistance.
they are pipes in form of a spiral shape :D
circular spherical shape
It was a circular shape !!!!!!!!!!!!!
the shape is circular
circular
Circular.
Circular
Circular
It is circular and curved
With rubber or circular foam that you can by from any hardware store
There is no shape which has only circular faces.