Annular Flow in Lined Pipelines

Abstract

Lining of a pipe with a polymeric liner is a viable trenchless technology for rehabilitating sewer pipelines. Polymeric liners are typically installed within the deteriorated segments of a sewer line, from one access hole to the next; to essentially create a new pipe within the old pipe without the need for excavation and removal. However, some concerns exist regarding the need to grout or seal the joints where the new liner connects with access holes and laterals. This study attempts to quantify the amount of flow within the annular space that could exist between a polymeric liner and a deteriorated host pipe. Results of full-scale field tests on twelve pipelines lined with four different deformed/reformed or fold-and-form (DR/FF) and cured-in-place-pipe (CIPP) liner products indicated that gaps of different sizes existed in all of the tested pipelines. These gaps resulted in variable annular flow between the liner and host pipe. Based on the results of the full-scale tests, a mathematical relationship was established between the annular flow in a lined pipeline and the annular space. The relationship between the annular flow rate and the average annular gap size depends on the difference in head between the entry and exit points along the pipeline. In turn, the average annular gap size depends on many factors including tolerances and imperfections in the host pipe and liner, conditions of the host pipe and the quality of liner installation. The results of the numerical analysis indicate similar flow rates for annular gap sizes greater than 1.3 mm (50 mils), which suggest tight installations of a liner into the host pipe to eliminate annular flow.