Page 101 - Trenchless Technology Piping Installation and Inspection

68 Cha pte r T w o

provides information on design methods and procedures for the
renewal of gravity and pressure pipes, for cured-in-place pipe
(CIPP) method. The data obtained from short-term tests cannot be
used for forecasting design life of plastic liner pipes. For predic-
tion of structural failure of flexible pipes, when subjected to an
external hydrostatic pressure, there are various methods available.
The most widely used approach involves the modification of the
Timoshenko equation covering the buckling of unconfined pipe
(Timoshenko and Gere, 1961).
Additionally, ASTM D2990-01, “Test Method for Tensile, Com-
pressive and Flexural Creep and Creep-Rupture of Plastics” pro-
vides a test of simply supported beam samples of plastic where
“creep modulus” is measured over 10,000 hours with extrapolating
long-term values. These data are used to define an apparent long-
term flexural modulus of elasticity for use in the buckling equa-
tions. ASTM D1598-02, ASTM D2992-06, and ASTM D2837-08 are
used to test pipe samples that are subjected to a varying internal
pressure to fail the lining pipes in 10,000 hours. Graph of hoop
stress with respect to time is plotted on the log scale and extrapo-
lated to determine long-term hoop stress on the existing pipe and
the lining. Table 2.6 presents the expected useful life of various
renewal methods in service life extension of the pipe based on vari-
ous publications indicated.

2.6 Summary
With the continued aging of existing pipelines and underground
infrastructure, the need for renewal of these pipelines is increasing.
The needs for improving quality of life, reduction of inconvenience to
the society make trenchless renewal methods more attractive for
pipeline owners and public agencies. The main benefits of trenchless
renewal methods are not only being cost-effective, but also these
methods provide environmentally friendly and sustainable con-
struction operations. Extensive project planning and background
assessment is required for proper execution of pipeline renewal and
replacement projects.
This chapter presented a summary of different trenchless renewal
and replacement methods with factors to consider when selecting a
specific method. These methods have become method of choice to
traditional open-cut pipeline installations and replacements. Trench-
less renewal and replacement methods stop leaks, resist corrosion
and abrasion, and install a new pipe in place of the existing and dete-
riorated pipe and provide a new design life. Pipeline replacement
systems can break or remove the existing pipe and install a new pipe
with the same or larger diameter without digging a trench. This chapter