A significant amount of engineering study has been undertaken and completed over the last 15 years with respect to the design of a flexible liner inside a buried gravity pipeline. This body of work has recently reached a point of consensus and is currently being developed into a new, more refined design practice for flexible liners in a gravity pipe application by a task group of the ASCE (thus making way for the long awaited retirement of the non-mandatory design appendix presented in ASTM F1216). The failure mode of a gravity pipe is well understood; and the addition of a liner has been shown to arrest the progression of the failure process. Recent improvements in CIPP technology have added tensile fiber reinforcement to the CIPP alternative and have thus advanced the opportunity for it to now be considered as a solution for renewal of existing pressure pipe applications such as sewer force mains and water mains. The research to date, however, on how liners interact with existing pressure pipe applications has been somewhat limited when compared to the work done with gravity pipe applications. Further, as these host pipes are often manufactured from ferrous materials, degradation of the host pipe can and often does continue to progress after lining of the pressure pipe has been accomplished. Thus the durability and reliability of a liner placed in a pressure piping application will require much more analytical work on the design engineer's part than has been required in the past for gravity designs to ensure that the intended service life of the liner will be achieved. This paper will introduce for discussion the fundamentals of the design approach for calculating the thickness and the types of reinforcing materials available for liner fabrication and the resin selection parameters for utilizing their strengths. The proper location and placement of the reinforcing material to sustain the long term steady static pressure and / or the pressure cycling of pump discharge pressure piping will be discussed.
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