Rehabilitation

RelinerCompletionDefining a Nationwide Problem with Concrete Transmission Mains – The catastrophic failure of Prestressed Concrete Cylinder Pipe (PCCP), manufactured to AWWA C301 standards, presents a significant challenge to Owners of large diameter water transmission systems in North America. Similar problems have surfaced in recent years in nuclear, coal-fired and gas-fired power generation plants that installed PCCP lines to transport water between cooling towers and condenser heat exchangers during construction.

While steel pipes have been in use for more than 150 years, with the first recorded installation taking place in 1858, composite concrete pressure pipes that make use of the tensile strength (prestressed or post-tensioned) of steel wire reinforcements, a very thin steel cylinder, and the compressive strength of concrete, first appeared on the market out of necessity during WWII due to steel shortages.

Vast amounts of post-WWII large-diameter pipeline infrastructure needs were met by PCCP, so their sudden and often premature failures present a formidable problem. Failures of PCCP first began in the mid-1950’s, and became more noticeable in the late 1970’s. Today, every owner of PCCP water transmission lines are budgeting for and implementing condition assessment and structural repairs of these systems.

A Proactive and Sustainable Approach – Municipalities grappling with failing PCCP can tackle the problem with a reactive approach in which individual pipe segment repairs or replacements are performed when risk of failure is judged to be imminent based on condition assessment. Or, they can undertake a comprehensive and proactive program in which all PCCP within a system is ultimately lined with steel cylinders over a 20- or 30-year period.

The comprehensive approach not only uses condition assessment and real-time-monitoring technologies, but also employs a risk-based analysis to determine the need for point repairs, such as removal and replacement of specific pipe sections; temporary repairs, such as carbon-fiber composites; or steel-cylinder lining of 1 to 5 miles of pipe at a time. Steel-based methods result in a new pipeline inside the structurally deficient host PCCP that will provide service life far in excess of 100 years.

Largest Water Purveyors Implementing PCCP Rehabilitation Programs – The San Diego County Water Authority (SDCWA) has completed the Reline of more than 40 miles of their 83 miles of PCCP as part of a 30-year asset management and capital improvements program with a budget of $780 million. The most recent public entity to institute and budget a 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. A reactive approach, instead of the comprehensive proactive one, would have cost MWDSC $5.5 billion.

Northwest Pipe Company is a leading manufacturer of steel based solutions for the rehabilitation of PCCP systems nationwide. Design of these systems meets the guidelines of AWWA M11, Manual of Water Supply Practices for Steel Water Pipe: A Guide for Design and Installation.

Based on the definition of Class IV Lining Category per AWWA M28, Manual of Water Supply Practices for Rehabilitation of Water Mains, the Relining and Sliplining systems are a structurally independent rehabilitation solution with a long-term (100 year) internal burst strength, when tested independently from the host pipe, equal to or greater than the Maximum Allowable Operating Pressure of the host pipe. The liners would also survive any dynamic loading or other short-term effects associated with a failure of the host PCCP due to continued external effects. In other words, Relining and Sliplining of the host PCCP lines results in a brand new steel pipeline inside the host pipe, installed via trenchless technology.