Relining is a steel-based rehabilitation solution for structurally deficient Prestressed Concrete Cylinder Pipe (PCCP). With 19,000 miles of PCCP systems in the ground throughout the United States, 4% of which are structurally deficient and in need of immediate repair according to the condition assessment industry, this amounts to many hundreds of miles of distressed PCCP. Once deterioration in a system begins, the decay typically continues. Premature failure of these systems are being prevented using fully structural renewal methods such as steel cylinder-based Relining.
An Understanding of the Relining Process – Relining is a man-entry process that involves inserting a collapsed steel cylinder into the deteriorating host PCCP, re-rounding the steel cylinders into place and performing fit-up by first welding each longitudinal seam, then welding the joints of adjoining sections, and grouting the annular space between the liners and host pipe with a cementitious grout. Relining requires entry and exit portals at the two ends of the pipeline being renewed, but it keeps excavation to an absolute minimum.
It’s a preferred buried pipe renewal method compared to traditional open trench options such as remove-and-replace, especially in highly developed urban areas. Cutting of roads and other structures on the ground creates havoc that can be avoided using these minimally invasive rehabilitation methods. The final step in installing Reliners typically involves the internal application of cement mortar lining, on-site, for long term hydraulic performance and corrosion protection.
#1 Reason to use Relining – When it is essential to not lose much internal flow area in the host PCCP, Relining is always the preferred rehabilitation technique, as long as the host pipe is large enough for man-entry, typically 54-inch and larger. It is typical to lose only 1-inch to 3-inch of internal diameter with Reliners on host pipes as large as 100-inch diameter and larger.
The collapsible cylinders used in Relining are specialized and labor-intensive to manufacture. Successful installation, or fit-up of Reliners within allowable tolerances specified by a designer requires specialized skill and is also more time consuming due to the longitudinal seams which have to be welded in the field, and the cement mortar lining that must be applied in the field. It is typical to successfully install 10 to 20 sections of 60-inch diameter Reliner pipe per day.
The steel-based lining of PCCP has been developed and tested in the field since the mid 1980’s. The San Diego County Water Authority (SDCWA) has been at the forefront of the development and refinement of relining technology. For a period of 25 years starting back in the early 1960s, SDWA installed PCCP throughout its water distribution system. After experiencing a series of catastrophic failures, SDCWA engineers developed the relining process in the mid-1980’s, and, in 1991, instituted a 30-year program to reline all of its 85 miles of PCCP.
SDCWA has currently relined more than 40 miles within its service area. The most recent Owner to institute and budget a similar comprehensive PCCP relining program is the Metropolitan Water District of Southern California (MWDSC), which will reline approximately 100 miles of PCCP over a 20-year period, at a cost of $1 billion. Using a reactive approach instead of a comprehensive proactive one would have cost MWDSC $5.5 billion to reline the same amount of pipe.Case Studies →