Line Stopping for Line Valve Installations on 55-Year-Old Aqueduct

The Cachuma Operation and Maintenance Board (COMB) operates the South Coast Conduit (SCC) from the Lake Cachuma north portal to the Carpinteria Reservoir. This pipeline is the primary source of water for the Santa Barbara, Goleta, Montecito, and Carpinteria Valley areas on the central coast of California. No redundant pipeline exists for conveyance of water supply to these communities when the pipeline needs to be taken out of service for repair or maintenance. In addition to any time needed to effect repairs on the pipeline, dewatering and rewatering this section of the SCC is a lengthy process. Due to the age and the material from which it is constructed, the pipe is difficult to repair or modify. Since 2004, three isolation valves have been installed utilizing the line stopping method. Line stopping is a process where a "hot tap" is performed on the pipe and a temporary plug is installed through the tap to stop the flow. Two line stops are required to isolate a pipeline section for removal and replacement with a section that includes a line valve. Temporary bypass piping is also required to allow flow to continue around the removed section of the main pipeline. The pipe on either side of the isolated section remains under full line pressure. This paper presents some of the design, construction, and operational issues attendant with the line stopping and lessons learned for application to the next three in-line valve installations planned.