You can draw curved pipes in a pipe network using the Network Layout Tools.
You can draw curved pipes when you are using 
Draw Pipes And Structures insertion mode or when you are using the Pipes Only insertion mode.
No matter which insertion mode you are using, the resulting curved geometry is equivalent to the AutoCAD arc object, where the insertion point (or start point) of the pipe, the midpoint, and the endpoint of the curved pipe can be gripped to edit the arc.
Curved pipe objects do not have persistent tangency once the curved pipe is created. Therefore, once a curved pipe is grip edited, any tangency to adjacent pipes may be lost.
Curve Creation Modes
You can use the default curve creation mode when you are using the Pipes and Structures insertion mode, or when you are using the Pipes Only insertion mode. If you already have a structure inserted, and you are adding a pipe to it, clicking on the structure specifies the initial direction and start point for the curved pipe. You are then prompted for an end point.
This method is used when the curved pipe is starting from a structure (or a null structure) with only one pipe already connected to it. With this method, the initial start point for the curved pipe comes from the structure. The start direction comes from the one pipe that is already connected to that structure. This ensures that the curved pipe will be straight to the last pipe drawn, or to a pipe that already exists at the structure (or null structure) from where the curved pipe is starting.
If no pipe is found to get a direction from, you are prompted to specify a direction at the first point.
Specifying Two Points and a Radius
Using this curved pipe creation mode, you specify the two endpoints of the curve and a radius. This method also lets you choose the curve direction (clockwise or counter-clockwise).
Specifying Three Points
Using this curved pipe creation mode, the first point is selected, then a point along the curve, then the curve endpoint.