What external coating is usually used to protect ducile iron pipe?

• A. epoxy coating
• B. bituminous coating
• C. polyurethane coating
• D. galvanized coating

Answer: (B)

External protection of ductile iron pipe from soil corrosion relies on a coating that forms a moisture barrier on the outside of the pipe. Bituminous coatings, such as coal tar enamel or asphalt-based coatings, have long been the standard because they adhere well to iron, stay flexible over a range of temperatures, are cost-effective, and pair well with the typical cement-mortar lining and joint assemblies used in underground installations. While epoxy or polyurethane coatings can offer strong protection in some environments, they are not the usual default for buried ductile iron pipe. Galvanized coating is not commonly used as the exterior protection for ductile iron pipe in buried service.