Long-term properties of cured-in-place pipe liner material

Water pipe infrastructure, especially cast iron and asbestos cement, are close to or past their recommended service life. Rehabilitation of this existing water pipe infrastructure is critical to reduce replacement costs and water loss. Cured-in-place pipe (CIPP) liners are one method of pipe rehabilitation, and long-term properties are integral in the design of CIPP liners for water pipes. Limited studies have focused on testing and reporting of long-term properties, which are essential for the service life design of CIPP products. This paper aims to investigate the long-term properties of a CIPP liner under service conditions (static pressure and pressure transients). Three types of tests, namely, creep, creep rupture, and fatigue tests, were examined. Results indicated that the creep retention factor (0.18-0.27) at 50 years does not correspond to the long-term rupture tensile strength reduction factor (0.7) at 50 years. Long-term creep degradation curves show that, when subjecting the liner to constant stress, the short-term strength of the liner remains close to the initial tensile strength. The long-term strength reduction factor due to fatigue (0.73 at 100 million cycles) suggests this CIPP material is less influenced by pressure fatigue cycles. Therefore, the creep retention factor is not a true estimate of rupture strength or fatigue strength reduction.