Ductile iron's superiority lies in its spheroidal graphite microstructure, as shown in microphotographs. Since the graphite structure of grey cast iron is linear, under severe loading, stress builds up unevenly around the ends of particles and weakens the metal. However in ductile iron, since the graphite structure is spherical, similar stress distributes evenly, thereby maintaining strength. Yet the basic chemical composition of ductile iron is similar to that of grey cast iron, giving it the same excellent anticorrosive properties. Together, these features give ductile iron, excellent resistance to impact, pressure and corrosion.

Ductile iron is the preferred pipe material because:

• Excellent corrosion resistance
• Superior mechanical properties
• Highly durable cement mortar lining
• Excellent workability – flexible, easy and quick to join
• Extremely long service life (75-100 years)
• High Hazen – Williams ‘C’ value of 140 over its lifetime - energy efficient