In older deteriorated
pipe systems, a cured-in-place-plastic (CIPP) liner can be installed to circumvent
pipe replacement. If the pipe is below the groundwater table, the liner can
experience external pressures from water that enters through holes and cracks
in the host pipe. If the pressure is high enough, the liner can fail prematurely
through buckling. The liner’s collapse resistance is also further reduced
if the host pipe contains defects, causing buckling failure to occur at an
even lower external pressure. Such defects include longitudinal intrusions
(dents), liner-to-pipe gap, pipe ovality, and others.
The objective of this master’s degree research is to develop a
3-Dimensional Finite Element model that determines the buckling pressure
of the thin-walled pipe liners that are installed in host pipes with longitudinal
intrusion defects. In the I-DEAS FEA package, a 12” pipe
with a liner thickness of 0.24” is being modeled. These values provide a
pipe diameter to liner thickness (DR) ratio of 50. The model also includes
a pipe ovality of 3% as well as a liner-to-pipe gap of 0.4%. The 3 values
of 2.25%, 4.5%, and 6.0% will be used for the longitudinal intrusion (defect
depth) variable. The 3 values of 0.05, 0.10, and 0.15 will be used for the
defect wavelength ratio (defect angle) variable. For each case, the defect
length will be varied from a lower bound (point defect) to an upper bound
(infinite defect length), and the model’s resulting buckling pressures will
be used to calculate a ratio of a defect liner buckling pressure to a perfect
liner buckling pressure. For an infinite defect length, the buckling pressure
results should converge on the solutions of the 2-Dimensional model of Zhu
and Hall.
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