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A Retrospective Evaluation of Cured-in-Place Pipe (CIPP) Used in Municipal Gravity Sewers (232 pp, 12.58 MB) (EPA/600/R-12/004) – January 2012

Pipe rehabilitation and trenchless replacement technologies have seen a steadily increasing use and represent an increasing proportion of the annual expenditure on operations and maintenance of the nation's water and wastewater infrastructure. Despite public investment in use of these technologies, there has been little quantitative evaluation of how these technologies are performing. The major reasons for retrospective evaluation of rehabilitation systems are needed include: data gaps in predicting remaining asset life of pipes and how long rehabilitation techniques can extend that life; and to assess whether the originally planned lifetime is reasonable based on current condition. The goals of this project were to draw attention to the need for this type of evaluation and to develop evaluation protocols that are technically and financially feasible for carrying out these evaluations.

The initial project focuses on cured-in-place pipe (CIPP) liners because they were the first trenchless liners (other than conventional slipliners) to be used in pipe rehabilitation and they hold the largest market share. The pilot testing used CIPP samples from both large and small diameter sewers in two cities that were in excellent condition after being in use for 25, 23, 21, and 5 years, respectively. Testing on the liners included thickness, annular gap, ovality, density, specific gravity, porosity, flexural strength, flexural modulus, tensile strength, tensile modulus, surface hardness, glass transition temperature, and Raman spectroscopy. In addition, environmental data was gathered as appropriate including: external soil conditions and pH, and internal waste stream pH. Three of the liners had already been in service for nearly half of their originally expected service life, but overall, there is no reason to anticipate that the liners evaluated will not last for their intended lifetime of 50 years and perhaps beyond.

Given the insights provided by the pilot studies, an expansion of the retrospective study is recommended to create a broader database to better define the expected life of sewer rehabilitation technologies. Specifically, it is recommended that the retrospective program be extended to: cover additional CIPP sample retrieval in other cities, pilot studies of other rehabilitation technologies; capture locally interpreted data from other cities; encourage sewer agencies to keep as-installed material test data for later comparison with follow-up testing; and adapt, develop, and/or calibrate non-destructive testing (NDT) methods that could use small physical samples that are easily retrieved robotically from inside the pipe.

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