Service Performance of a Cured In Place Polymer Pipe Liner for Deteriorated Cast Iron Pressure Pipes
Although Cured-In-Place Pipe (CIPP) liners have been used extensively across North America, their in-situ performance in deteriorated pipe conditions has not been extensively studied. The purpose of this research work is to develop a better understanding of the service performance of CIPP liners in cast iron water pressure pipes by experimentally quantifying the hoop and axial strains in the liner when exposed to various loading conditions. In this research, the application of distributed optical fiber sensing to study the mechanical properties of a commercially available structural CIPP liner used for pressure pipe repair was demonstrated. Using distributed strain sensing, large-scale experimental investigations were conducted to evaluate the mechanical response of a CIPP liner where it spans across localized areas of failure in the host pipe (i.e. perforation and ring fracture) by quantifying the strains in the liner. Axial strain measurements obtained from surface bonded optical fibers support the use of the current ASTM F1216-16 design rules for pressure pipe liners spanning across small sized perforations (up to 50 mm in diameter in a pipe with a 154 mm overall diameter). However, ASTM F1216-16 design recommendations produce unconservative estimates for larger perforations (up to 75 mm diameter in a pipe with a 154 mm diameter). For the case of a liner which spans a pre-existing ring fracture in a host pipe subjected to angular rotation, it was observed that the location of maximum opening in the fracture is the critical location where the liner could experience failure. Results also showed that debonding (i.e. separation between the liner and the host pipe) decreases the maximum strains in a liner and that the extent of debonding is impacted by internal pressure and alignment of the pipe across the fracture. Due to the polymeric nature of the liner, the tensile creep properties of the liner were investigated. Results suggest that the use of an industry-accepted 50% creep retention factor to estimate the 50-year service life of a liner could produce unconservative results.