- It is not possible to provide a specific answer to this question, because the corrosion rate of any material is defined by the corrosivity of the soil in which the material is imbedded. DI is not infallible, DI corrodes. At one corrosivity level, corrosion rates are: 0.8 mil/year for DI, and 3.0 mils/yr for steel. Absolute corrosion rates vary from site to site, defined by local corrosivity levels. But, many field tests have shown that the differential between these corrosion rates remains relatively constant at all corrosivity levels. That said, if a steel pipe system will last 30 years, a DI pipe system will last ±110 years, in the same soil.
In an effort to more clearly show these differences, PNP has included photos below showing the results of these different mechanisms, under actual field conditions.
Both DI and steel pipe and fittings were relocated in 2015, after seven (7) years of service, to accommodate trail widening operations. This photo shows the amount of corrosion for both materials, IN THE SAME SOIL CORROSIVITY.
Why Ductile Iron Pipe?: The collage of photos attached, shows the condition of FBE coated steel pipe, which had been installed as new clean pipe, after 7 years of service. This photo shows the “scaling” and “pitting” processes, occurring continuously in normal stages of corrosion with steel.
A 24″ .375 wall coated steel water pipeline after seven years of service.