In municipal projects such as water supply, drainage, and gas transmission, pipelines serve as the "lifeline" that ensures the smooth operation of cities. Ductile iron pipes are widely used due to their high strength and toughness. However, many people wonder: since ductile iron pipes are buried underground for long periods, are they prone to rust and corrosion? Just how corrosion-resistant are they? This article reveals the answers.
The "Dual-Layer Protective Armor" of Ductile Iron Pipes
The corrosion protection of ductile iron pipes is achieved through a scientifically engineered dual-layer protection system.
Outer Corrosion-Resistant Coating
Zinc Layer + Asphalt Coating: The standard corrosion-resistant coating consists of 130 g/m² of zinc plus a 70 μm asphalt paint finish. A dense zinc layer is formed on the surface of the ductile iron pipe through a zinc spraying process. Zinc acts as a "sacrificial anode," reacting preferentially with corrosive media to protect the iron substrate; the outer layer is then covered with an asphalt coating to isolate moisture and chemicals in the soil.
The cement lining of ductile iron pipes is applied using a centrifugal coating process. The lining material consists of ordinary Portland cement mortar, which acts as an active anti-corrosion coating that releases alkaline substances upon contact with water. This not only prevents water-induced corrosion but also inhibits scale formation, ensuring the safety of water transmission.
The "Corrosion-Resistant Gene" of Ductile Iron
Unlike traditional gray cast iron, ductile iron transforms the internal graphite structure from flake-like to spherical by adding elements such as magnesium and rare earths. This structure significantly reduces micro-pores and cracks within the material, thereby lowering the likelihood of corrosion-causing agents penetrating the material. Ductile iron pipes that comply with national standards can have a service life of over 50 years in typical soil environments, with corrosion resistance far exceeding that of ordinary steel pipes and plastic pipes.
Plastic pipes: Low pressure resistance; prone to aging over time.
Standard steel pipes: Prone to rust; require frequent maintenance; high overall cost.
Ductile iron pipes: Mature anti-corrosion technology; although the initial investment is slightly higher, their long service life and low maintenance costs make them a significantly better value over the entire lifecycle.
As the "invisible guardians" of modern engineering, these pipes utilize material innovations and process upgrades to create a comprehensive corrosion-resistant system that protects them from the inside out. Whether for everyday water supply or projects in harsh environments, ductile iron pipes safeguard the city's underground infrastructure with their consistent performance.