Page 81 - Trenchless Technology Piping Installation and Inspection

Existing Pipeline Renewal and Replacement Methods 51

• Flow capacity problems arising from pipe internal tuberculation
and deposits: Lining must present a smooth surface to the con-
veyed liquid, which helps maximize the flow capacity of the
lined pipe. Due to extremely low friction coefficient of the
new liner, it is possible to increase the hydraulic capacity of
heavily tuberculated pipes.
• Leakage from corrosion holes and failed pipeline: Lining must pro-
vide a continuous and pressure-tight envelope inside the
existing pipeline which must be designed to effectively span
corrosion holes and joint gaps.
• Vacuum Collapse: Ensure that the liner will not collapse if the
lined pipe is subject to an internal vacuum during the service.
• Groundwater level is above the invert level of the existing pipe: The
groundwater may enter the annulus of existing pipe and liner
through leaking joints/corrosion holes, and others in the
existing pipeline. The resulting external hydrostatic pressure
of water on the liner has the potential to cause the liner to
collapse (buckle).

Sample design calculations are presented at the end of this chapter.

2.3 Applicability of Trenchless Renewal
and Replacement Methods
Trenchless renewal and replacement methods can be used to line,
rehabilitate, upgrade, or renovate (collectively called renewal methods)
existing pipelines. There are also methods that can replace and/or
enlarge existing pipelines in situ. These methods are collectively called
in-line replacement methods. Throughout this book, the term “renewal”
is used when lining methods are applied to extend the design life of
pipelines. When trenchless methods are used to repair pipelines
without extending their design life, the term “repair” is used. The
basic trenchless renewal and replacement methods are presented in
Fig. 2.3 and can be categorized according to their application for grav-
ity and pressure pipes, as presented in Table 2.3.
Factors to be considered while implementing any pipe renewal
and replacement method and how the method is advantageous over
other competing techniques include:

• Social cost
• Life span (durability)
• Reliability
• Environmental impacts