Internal PCCP Force Main Deterioration—Analysis and Rehabilitation

Abstract

and was constructed in 1979. The nominal inside diameter is 1350 mm (54") and the pipeline was designed as a sewage force main. In 1999, approximately 75 m (246 feet) of the pipe failed and was replaced with HDPE pipe. In 2008, an internal inspection was conducted downstream of the failed section. The inspection was conducted using man entry and by close circuit television (CCTV). The inspection found five (5) pipe sections under severe corrosion attack where the interior concrete surfaces near the crown of the pipe had deteriorated exposing the reinforcing. Another nine (9) sections also showed early signs of H 2 S attack. A post inspection hydraulic analysis indicated the deteriorating pipe section does not flow full, and the hydraulic regime along this section is supercritical transitioning to subcritical resulting in a hydraulic jump forming within the pipe. The wastewater contains high concentration of sulfides. The turbulent flow conditions at the hydraulic jump exacerbate the release of H 2 S gas from the aqueous phase to the air phase. The H 2 S gas collects near the crown of the pipe and initiates corrosion attack on the concrete surface. A rehabilitation strategy was developed to extend the service life of the PCCP force main.