There doesn't currently seem to be a pipe part to correctly represent the shape arch pipe. Pipes are still very new in C3D so I'm sure there will be more parts available in future releases.
In the mean time, if you don't need an accurate representation of the arch pipe in a cross-sectional view you could take the horizontal elliptical pipe, save it as a new part family, edit the description and part sizes to come up with a pretty good approximation for use plan and profile views. You may have to make some alterations to the sizing calculations to match the height/width proportions of an arch pipe.