The San Diego County Water Authority (SDCWA) faced a daunting task when the pre-stressed concrete cylinder pipe (PCCP) in their system began to fail. The strength of PCCP comes from steel wire wrapped around a steel shell. A coating of Portland cement gives the pipe stability as well as corrosion protection. However, if the cement cracks and corrosion attacks the wire, the pipe can fail catastrophically. Many such failures have occurred over the last few decades. As a result, agencies are aggressively replacing PCCP with a more reliable material. For San Diego County, solving the problem of their 50-plus miles of failing PCCP is a massive task.
The Rancho Penasquitos portion of Pipelines 3 and 4 relining bid in July of 2003. San Diego County Water Authority chose J. F. Shea to complete this section. Not only was this job complex in scope, the Water Authority also required Pipeline 4’s reline to be completed by April, 2004, and Pipeline 3 to be in place five months later. Liquidated damages were costly, so it was critical to select a steel pipe supplier that was up to the task. Shea selected Northwest Pipe Company because of our ability to produce the material quickly and efficiently. Northwest Pipe’s years of industry experience, past projects with both the agency and contractor, and its fully equipped ISO 9001:2000 facility in nearby Adelanto, California, made the company an ideal choice. SDCWA inspection personnel were on site while each can was manufactured and tested. J. F. Shea and Northwest Pipe coordinated daily shipments since narrow right of ways limited storage on the job site.
Relining portions of Pipeline 3 and 4, Rancho Penasquitos is part of a 24-year plan to line or replace the Authority’s entire PCCP infrastructure. The project presented many challenges. Forty-foot access portals were created along the existing route by removing two segments of the PCCP pipeline. The liners specified were rolled and welded steel pipe “cans” that were collapsed prior to installation in order to fit through the sloping curves of the existing pipeline. The liners for this project were then expanded in place along the 33,000-foot pipeline. Pipe segments ranged in diameter from 63 to 93 inches–a mere 3-inch reduction from the original PCCP diameter. Complex installation techniques meant each pipe was, in essence, a custom fabricated piece. Because the final welding was performed in the PCCP pipe, back-up bars were installed longitudinally down each can seam to accommodate an internal full fillet weld. Each steel can and its bell and spigot joint had to be custommanufactured to match the exact joint locations of the existing PCCP pipeline.
After the liner segments were placed, the annular space between the liner and the existing pipe was filled with cement grout. Steel grout rings were used to limit the pressure during the process, where grades reached as high as 38%. To reduce the hydraulic head in the annular space between the reliner and the PCCP, the rings were completely welded between the reline section and the existing PCCP joint rings. The process required each ring to be completely welded prior to the next joint installation. Grout ring locations were designed as close as 20 feet apart in the steepest sections. The final steps in the installation process required lining the entire pipeline with cement mortar and then installing factory lined-and coated steel pipe in the portal openings.
When San Diego County Water Authority sought a solution to its crumbling infrastructure, they turned to rolled and welded steel pipe manufactured by Northwest Pipe Company. By collaborating with the installation contractor and owner, Northwest Pipe Company ensured a high-quality pipe, delivered on time, for this critical project.