Page 208 - Trenchless Technology Piping Installation and Inspection

172 Cha pte r F o u r

The main use of ductile iron pipe is in water systems. However,
the availability of thermoplastic and thermoset pipes and newer sub-
stitute materials represents some significant competition to ductile
iron since the late 1960s. The newer materials are lighter (where this
might be judged an advantage), in some cases less expensive, and
perform many of the required functions within a distribution system.
Above all, plastic pipes are inherently suited to withstand most forms
of both internal and external corrosion that can be a concern to unpro-
tected ductile iron pipe in some service environments.
However, corrosion problems for ductile iron pipe can overcome
by the use of appropriate corrosion protection. The protection meth-
ods include cement mortar or polymer linings for internal corrosion
protection, maintenance of flow properties, and polyethylene encase-
ment per ANSI/AWWA C105/A21.5, or in uniquely aggressive
environments cathodic protection, for external corrosion. A newer
approach to iron pipe corrosion control, called the design decision
model (DDM), has been developed by the Ductile Iron Pipe Research
Association (DIPRA). This method tailors the chosen corrosion pro-
tection method of the pipeline based on several factors including
substantial history, the corrosion potential of the specific environ-
ment involved, and the critical nature/priority of the specific pipe-
line involved.
In recent years, various manufacturers have also developed
restrained joints for ductile iron pipe; therefore, the industry is able to
offer its products to the trenchless construction industry. Today ductile
iron pipe can be used for HDD, pipe bursting, casing and carrier pipe
installation, and sliplining. The use of ductile iron pipe in sewer systems
is less in comparison to its use in potable water distribution and trans-
mission. Nevertheless, some municipal agencies use ductile iron pipe
for their gravity flow applications. Flexible, restrained joint ductile iron
pipes are particularly attractive for some HDD installations. In HDD
applications, joints can rapidly be assembled in field conditions with
minimum equipment or highly skilled technicians. The pipe also can be
installed with limited access, and need not be bent (nor result in high
bending stress/strain) when installed in a normal curved drill path.
Ductile iron pipes are flexible conduits and are designed and
installed accordingly. However, when internal cement-mortar lining
is specified, the vertical deflection of the pipe is limited to 3 percent
instead of 5 percent. Ductile iron pipes with flexible linings, such as pro-
prietary ceramic, epoxy, and fusion-bonded epoxy primer/heat-fused
polyethylene topcoat linings are limited by ASTM A716 and A746
standards to 5 percent deflection.

Cast-Iron Pipe It is important to have an understanding of the prede-
cessor of ductile iron pipe, the cast-iron pipe. Cast-iron pipe has been
used throughout the world for many years in portable water systems.
In the United States, cast-iron pipe was introduced in the early 1800s.