Environmental Engineering Reference
In-Depth Information
4.8.5.1.2 ductile Iron Pipe
Ductile iron pipe resembles cast iron pipe in appearance and has
many of the same characteristics. It differs from cast iron pipe in that
the graphite in the metal is of a spheroidal or nodular form; that is, it is
in a ball-shape form rather than a flake form. Ductile iron pipe is strong
and durable; has high flexural strength and good corrosion resistance;
is lighter weight than cast iron; has greater carrying capacity for the
same external diameter; and is easily tapped. Ductile iron pipe, however,
is subject to general corrosion if installed unprotected in a corrosive
environment (Gigliarda and Liberatore, 2000).
4.8.5.1.3 Steel Pipe
Steel pipe is sometimes used as large feeder mains in water distribu-
tion systems. It is frequently used where there is particularly high pres-
sure or where very large diameter pipe is required. Steel pipe has high
tensile strength and offers lower costs; it is relatively easy to install, is
good hydraulically when lined, and can be adapted to locations where
some movement may occur. Steel pipe, however, is subject to electroly-
sis and external corrosion in acid or alkali soil and has poor corrosion
resistance unless properly lined, coated, and wrapped.
Note:
The materials of which street wastewater (sewer) pipes are most
commonly constructed are vitrified clay pipe, plastic, concrete, and
ductile iron pipe; however, ductile iron pipe is most commonly used in
wastewater collection, primarily for force mains (e.g., interceptor lines)
and for piping in and around buildings. Ductile iron pipe is generally not
used for gravity sewer applications, however.
4.8.5.2 Maintenance Characteristics of Metallic Piping
Maintenance of metallic piping is determined in part by charac-
teristics of the metal (i.e., expansion, flexibility, and support) but also
includes the kind of maintenance common to nonmetallic piping sys-
tems, as well. The major considerations include:
• Expansion and lexibility
• Pipe support systems
• Valve selection
• Isolation
•
Preventing
backflow
• Water hammer
• Air binding
• Corrosion effects
