Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Most damaged pipelines are structurally safe, but due to hydraulic requirements renovations are required. One solution is to apply an internal polymer liner. The critical external fluid pressure at which the liner may collapse is the target of this research. The Finite Element Method (FEM) is used and a rigorous non-linear interaction analysis allowing for large deformations and material plasticity is developed. Liners are assumed to be either perfectly circular or circular with some initial local or global geometrical imperfections. The typical local imperfection is defined as a wavy intrusion into the liner. The global imperfections take the shape of an ovalization in the damaged host pipe or an eccentric position of the loosely fitted liner relative to the damaged pipeline. A parametric study is undertaken to determine the effect of the geometrical parameters (e.g. liner thickness to radius ratio, imperfection size, ovality and size of gap between the liner and the host pipe). A comparison is made with experimental data available for circular liners, and there is good agreement with the numerical solution.;It is shown that critical external fluid pressure depends heavily on the ratio of liner thickness to radius. Thick liners experience a modest stability increase as a result of host pipe support compared to the significant stability increase for thin liners. Local geometrical imperfections have a very substantial effect on the buckling strength. The imperfection sensitivity is particularly significant for thin liners. Ovalling in the host pipe decreases stability somewhat relative to circular host pipes. Stability of loosely fitted liners degrades seriously if a significant gap exists between the liner and the host pipe, particularly when the liner is thin. Generally, the pressure which causes yield in the liner materials represents the peak value that the structure can sustain, and inelastic stability can reasonably be estimated using that point of first yield. The current ASTM design practice employs a single stability value for all liners which is not conservative for thick liners. The thesis presents an efficient new design approach based on the parametric study which includes the effect of the liner thickness to radius ratio, liner ovality, and local imperfections.



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