Key Questions to Ask When Ordering cast iron double flanged pipe

2. Why are all Ductile iron pipes “painted black”?

The metal known as copper readily oxidizes when exposed to moist ambient air forming an egg-shell-thin yet highly protective green patina on its surface. The best example of this over time is the Statue of Liberty, located in the New York Harbor for nearly 200 years. Her ⅛-inch thin original skin has not diminished over her significant time in the harsh marine conditions, mainly due to the naturally occurring patina.

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The simple fact is - oxidation is not rust. Rust is a destructive form of metal disintegration over time. Oxidation happens and then remains stagnant and protective of the substrate to which it is attached unless ambient conditions become more corrosive than oxidation can resist.

While the green patina of copper offers a highly desired visual appeal, the same oxidation process upon the surface of a Ductile iron pipe results in varied shades-of-cinnamon splotchy appearance upon its entire surface. This annealing oxide layer on DI pipe and fittings, much like the patina on copper, is so thin it’s barely measurable yet serves to prevent deeper pitting or degradation of the metal in standard ambient conditions.

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The problem is, unlike copper, it's not attractive to the eye, and therefore, all Ductile iron pipes are coated with an NSF-61 certified asphaltic-based paint known as sealcoat. Water-based sealcoats are common today and are much friendlier to the environments of the foundry and the external world.