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Cured in place pipeliners, in the normal case of underground sewers, are designed to withstand hydrostatic loading due to external groundwater pressure. In addition, some liners may be designed to resist the effects of soil loading and loads superimposed on the soil loads (e.g., traffic loads).
Except in significantly out-of-round pipes (e.g., ovoid pipes) the failure mode of pipeliners is considered to be due to buckling. Further, pipeliners are designed to transmit flow in the pipe as efficiently as possible, taking into consideration the relative smoothness of the walls and loss of cross-sectional area. Pipeliners are designed to significantly reduce infiltration and exfiltration to and from the surrounding soil.
Impregnation issues are associated with the bunching up of the inner liner(s) and are unacceptable.
Coating-related issuesAn aspect of atypical features associated with coating-related problems is that of minor distortion of surfaces. This aspect is of no consequence either hydraulically or structurally.
Inward folding of the lining An aspect of atypical features associated with inward folding of liners is a dramatic loss of cross sectional area. Not only is this of significance hydraulically, but also because the circular cross-section with close tolerance to the existing pipe wall required for buckling resistance is lost. This is potentially a serious problem, but can in favorable circumstances be overcome by inverting a dry liner through the problem liner and circulating hot water. This should soften the liner sufficiently so that it can be reshaped. Do not apply a high head until hot or the liner may crack. As a last resort, the lift section may need to be cut out completely and a new length of liner installed.
Damage to the surface of liners can be caused by a range of factors. The coating can be ripped and gouged by sharp objects used for rope end/soft end fittings. Alternatively, damage can be caused to the coating by dragging the liner over rough surfaces. In any case, if such damage results in water leaks, then it is unacceptable and should be repaired.