Curing Process

The uncured resin is designed so that, once the liner has been installed, the curing process can completed while the liner is held against the interior of the host pipe and within a reasonable length of time. The simplest approach is simply to allow the resin to cure under ambient conditions (i.e. at the temperature that will be present when the liner is installed in the host pipe). This can work but is much slower than the other approaches used and may be vulnerable to unexpected temperature variations during installation. The most common curing process used for CIPP liners has been a hot water cure. In this approach, hot water is used to both inflate the liner against the host pipe and to initiate the resin cure. To speed liner cure, steam can be used instead of hot water for the cure with the steam pressure inflating the liner rather than the hot water pressure. The curing process for resins is exothermic and hence this heat released contributes to the curing process once the curing is initiated. Resins can also be designed to have the cure initiated using ultra-violet light. This type of liner has a long shelf life, is inflated by air pressure and has the light train inserted within the inflated liner to accomplish the cure. For specialized applications, the heat from electric wires embedded in the liner can be used to initiate the cure. Combinations of curing can also be used – for instance for very thick liners. Control of the liner installation and curing process is important for consistent and high quality liners. Embedded temperature sensors can monitor the thermal evolution of the liner during curing to make sure that adequate curing is achieved. The ultra-violet cure system allows an inspection of the full length of the interior of the liner before the curing process is started.