Use of optical fibers to investigate the performance of pressure pipe liners spanning across a ring fracture

Abstract

Cured in place pipe liners have been used in the rehabilitation of cast iron water pipes for over twenty years. Previous research has established that the liner’s performance may be controlled by local strain concentrations that develop where the liner spans across a ring fracture in a pipe subjected to differential ground movement. This paper reports on the application of distributed strain sensing using optical fibers to quantify the longitudinal strain distribution along the inside surface of a polymer composite liner. It was confirmed that the location of maximum opening in the fracture is the critical location where the liner could experience failure. The measurements quantify how debonding (due to slip and separation between the liner and the host pipe) decreases the maximum strain in a liner and how the extent of debonding is impacted by internal pressure and the alignment of the two pipe segments across the fracture. At rotation angles of approximately 0.3°, longitudinal strains of up to 17,000 microstrain were observed in a liner subjected to internal pressure of 600 kPa. Findings from this investigation confirm that the behavior of CIPP liners installed in pressure pipes containing pre-existing ring fractures, and subsequently subjected to angular movements, should be considered in design standards.