Self-supporting pipe installation solves recurring water main problem
The city of Pasco, Wash., faced the challenging job of solving a recurring water main problem. The leaking 12-in. pipe was located under an active railway intersection on the southeast side of the city. But, thanks to a well-planned effort, the deteriorated pipe was successfully rehabilitated within a tight time frame, increasing the functionality of Pasco’s water supply system.
A Tough Fix
In 2011, the city of Pasco realized the need for a long-term solution involving two sections of a deteriorated 12-in., lead joint, ductile iron pipe running 8 ft under six sets of Burlington Northern railroad tracks. About five years ago, Pasco was forced to temporarily reroute the water supply due to the leaking joints and externally corroded cement pipe. Open-cut construction was out of the question. Due to the constant traffic, the importance of the switching yard on the southeast side of Pasco and because the railway is a major intersection of railways on the West Coast, shutting down the yard to repair the leaking pipe was not an option. Equally as important, three of the rails immediately cross the Columbia River on one of the few bridges providing access to the south.
In addition to the construction site conditions was the regulatory issue that required NSF-61 approval for the drinking water supply pipe. In water main rehabilitation projects, it is often the tight time frame for the renovation that determines the decision on the method or service provider.
Ultimately, the city of Pasco instructed Michels Pipe Services, a SEKISUI NordiTube licensee, to rehabilitate the circa-1945 water main pipe by the cured-in-place pipe method. The liner chosen was NORDIPIPE. Combining the individual components of fiberglass, needle felt, epoxy resin and PE coatings, the liner is able to withstand extreme stress. Thanks to a fiber- glass layer, it has statically self-supporting properties, enabling it to withstand high internal pressures up to 250 psi depending on the diameter. It also can withstand general external loads and is structurally self-supporting, even without the old pipeline.
The installation of the liner commenced in October 2011 without any impact on rail traffic. The project consisted of two similar installations, each with an entry access pit on one side of the railroad tracks and a receiving pit on the other side of the tracks. The liner was prepared in Michels’ Salem facility and transported to the site overnight, reducing the time between activating the epoxy resin and the actual pipe installation. Additionally, costs were reduced by preparing the liner in Salem as opposed to assembling an onsite wet-out area. This was a unique benefit, considering most epoxy methods require onsite resin preparation.
What took years of rerouting the water main supply for the city of Pasco was repaired in two days. The installation project was tackled in two separate 275-ft sections. By using a pressure vessel to invert the tube and curing it with steam to a statically self-supporting pipe within a pipe meeting AWWA Class IV standards, each installation took 12 hours. End seals were used to join the liner to the existing ductile iron pipe, and, after a 150-psi pressure test, the pipe was returned to service to extend its operation for the next 50 years.
The rehabilitation went as planned in spite of some challenging conditions; for example, different end seals had to be manufactured on an emergency basis to meet the tight timeline. But all parties involved made adjustments on the project to compensate and complete it on time. Both the city of Pasco and Burlington Northern Railroad were pleased with the outcome.
“The city now has an operational line that increases the functionality of its system, and the only excavation was to provide access to the pipe on each side of the rail crossings,” said Robert Blain, associate engineer II with the city of Pasco. “No rail traffic was affected by the tailor-made pipe lining and the economic and time savings are substantial.”
The actual difference of time for the onsite construction was two days for the cured-in-place pipe liner in comparison to 14 days for open-cut construction. The difference between shutting down the railway traffic was even more drastic: eight days versus zero days, with this liner.
http://www.wwdmag.com/sites/default/files/imagecache/article_slider_big/Picture%20092_10x15.jpeg.jpgInstallation of the liner did not disrupt rail traffic.
http://www.wwdmag.com/sites/default/files/imagecache/article_slider_big/Picture%20109_10x15.jpeg.jpgThe crew used a pressure vessel to invert the tube and cure it with steam to a statically self-supporting pipe.