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Western Dam Engineering Technical Note May 2016 9 You Down with CIPP? – Yeah! You Know Me! Introduction Cured-in-place pipe (CIPP) is becoming a more common method used to rehabilitate deteriorated outlet piping on dams, and offers many benefits over other pipeline rehabilitation methods. CIPP has been successfully used in renovating deteriorated pipelines, drain pipes, and conduits through levees and has been used for conduit renovation through embankment dams since about the mid-1990s [5]. The CIPP system consists of a flexible fabric tube and a resin system that is hardened by a curing method. The resin is the primary structural component of the system. A fabric tube is used as a means to install and temporarily support the resin until it is cured in place. The CIPP liner resin is typically injected into the fabric (“wet- out”) at the manufacturing facility for quality control and shipped to the project site, where it is cured after installation. The fabric tube and resin systems vary depending on the CIPP manufacturer and the design of the CIPP. Some common fabric tube materials are polyester felt and glass fiber composite cloth. Some common resin systems are unsaturated polyester, vinyl ester, and epoxy. CIPP is installed inside an existing pipeline by either an inversion method or a pulled-in- place method. After the CIPP is installed, it is cured in place using one of several available techniques and forms to the shape of the existing pipe, including minor irregularities. This article presents some considerations for selecting and designing an effective CIPP system for pipeline rehabilitation. CIPP Selection Considerations Selecting the right rehabilitation method needs to consider the cause of the deficiency prompting the repair. Pipeline repair can range from isolated repairs of a leaky joint or crack, to more global rehabilitation of a deteriorated pipe. A known construction defect that resulted in an open joint could warrant isolated repair using expandable bands or grout; whereas, deterioration due to general aging of the pipe would warrant a more global rehabilitation. CIPP is most often considered as a global rehabilitation method. Although segment lining is possible (lining only a portion with CIPP), it induces greater hydraulic irregularities within the pipe and cost inefficiencies associated with an isolated repair as compared to other alternatives. Global rehabilitation with CIPP can be compared to other common methods such as remove-and-replace using cut-and-cover techniques or slip lining. See the previous Western Dam Engineering article for additional considerations on outlet conduit rehabilitation: Low-Level Conduits - Rehab or Replace?. Table 1 summarizes a few key considerations when initially screening the viability of CIPP as a potential rehabilitation method. Table 1. Considerations for Evaluating Suitability of CIPP as a Viable Pipe Rehabilitation Method Conditions Considerations Pipe Pressure CIPP can be a good option for pressurized pipes because of the jointless installation but both internal and external pressures need to be taken into account during the design. Host Pipe Alignment CIPP is suitable for pipes with gentle bends; however, certain curing methods work better under certain conditions. Steam curing is best for long runs of steeply sloping pipe to avoid excessive hydrostatic pressure. Water curing is best for pipes with bellies since steam condensation can accumulate in bellies, preventing proper curing due to cooling at those locations. CIPP is not suitable for pipes with significant bends or changes in diameter. Flow Conditions Pipes should be fitted with proper venting to prevent cavitation and negative pressures that could damage the lining. Degree of Pipe Deterioration Can be used for partially to fully deteriorated pipes; however, not well-suited for deformed/collapsed pipes. Pipe Size CIPP can be installed in pipes from 4 to 108 inches in diameter and up to 3,000 feet in length. Liners on the upper end of this range have practical limits due to material handling and transportation limitations as the liner needs to be shipped in one piece. Access Access to both ends of the pipe is typically required, regardless of curing method. Site access for equipment mobilization and efficient installation are also considerations as different curing methods require significantly different equipment. Climate May influence selection of curing methods and related resin.