Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 2—Conduit Materials2.3.2 Ductile-iron.Ductile-iron pipe is manufactured by centrifugal casting. A controlled amount ofmolten iron is introduced into the rotating mold, which generates a centrifugal forcethat holds the iron in place against the mold until it solidifies. The pipe is thenremoved and furnace annealed. Ductile-iron has greater range of deformation, and isless brittle than cast-iron pipe. Ductile-iron pipe also has greater tensile andcompressive strength than cast-iron pipe. Linings and coatings are required forductile-iron pipe; commonly asphalt paint and cement-mortar lining are used. Thefirst manufacture of ductile-iron pipe was in 1955. Ductile iron has been commonlyused in utility water and sewer systems. Ductile iron is used infrequently in conduitapplications. Ductile iron pipe is available in diameters up to 64 inches and inlengths up to 24 feet.The advantages of using ductile-iron pipe for conduits include:• Manufactured to tight tolerance in a controlled environment.• Long service life, if proper linings and coatings are used.• High tensile and compressive strength.• Flanged joints (figure 29) provide improved watertightness over bell and spigotconnections.Figure 29.—Flanged joints of ductile ironpipe improve the watertightness of thejoint.53