I share with you the craft work of a PipeDesigner user to develop some pipes for his 50cc race moped.
He starts with the realization of an header in order to test his equipment, to see how the metal sheet is deforming and the modifications of the curvature of the pipe center line.
Then, he cuts the two half pipes, bend the side at 90°, weld the sheets together. When the high pressure and purge valve are on, starts the shape building.