Stress Analysis for a Liner Spanning a Gap between Sections of Rigid Pressure Pipes

Liners are being used with increasing frequency to rehabilitate cast iron and other metal pressure pipes. The liner will span across any gaps between different pipeline segments, requiring consideration of the stress that develops in the liner at those locations. In this study, cylindrical shell theory was used to develop closed-form solutions for stresses in the liner, considering two limiting conditions at the edge of the gap: simply supported and encastred. The closed-form solutions for stress were then checked using finite-element modeling, with results shown to be within 2.8% when both edges were pinned, and 4.3% when both edges were encastred. Liner stresses were then examined for a range of different diameters and internal fluid pressures. Finite-element modeling was then extended to consider the zones of liner beyond the edges of the initial gap, with the liner separating from the host pipe over a distance adjacent to the edges of the gap that depends on the internal fluid pressure. The finite-element results were effectively normalized using an approach inspired by the new closed-form solutions, and a new curve fit was developed to provide values of maximum effective stress based on those normalized finite-element results, with R2=0.9437. The finite-element calculations provide a liner condition at the edge of the gap that is between fixed and simply supported (featuring some rotation and some moment). The solution was demonstrated to be superior to a previous solution presented in the literature that had issues with dimensions, and that does not effectively match the finite-element calculations.