Ductile Iron pipe is stronger, easier to tap, requires less support, and provides greater flow areas compared to pvc pipe. These are just a few of the advantages that Ductile Iron has over pvc pipe. For more information, please review the document links below:

Ductile Iron Pipe versus PVC
Ductile Iron Pipe versus pvco
Hydraulic Analysis of Ductile Iron Pipe
DIPRA Seminars / Lectures
Direct Tapping Comparison Study: Ductile Iron Pipe versus Polyvinyl Chloride Pipe
A Comparison of Engineering Considerations for Pressure Pipe

Take A Look At These Links To Find Out More

Why Ductile Iron Pipe is Superior to Concrete Pipe
Why Ductile Iron Pipe is Superior to Polyethylene Pipe
Why Ductile Iron Pipe is Superior to Steel Pipe