Critical PCCP Pipelines Montreal Program
Critical large-diameter water transmission mains frequently run beneath city streets in busy urban environments. Like the majority of water infrastructure across North America, these pipes are reaching the end of their design life. However, pipelines in urban environments pose a significantly greater risk and challenge to water utilities.
These pipelines are high-risk because of their high consequence of failure; if a pipe beneath a busy downtown street fails, the repair costs can quickly escalate and the failure causes a massive disruption to businesses and commuters. In some cases, failures in urban environments have cost utilities upwards of $5 million to remediate. A failure not only carries a high repair bill, but contributes to a negative public perception of the utility which can harm consumer confidence and lead to negative public relations.
With such high risk, utilities often prioritize these mains ahead of those with lower consequence of failure. However, because these mains are located in high-traffic areas, assessing them is far more challenging than assessing a linear main in a rural area.
Dealing with above ground obstructions, commuter delays and a lack of access points means that operators need to have close control over inspection technologies. In addition, the technology must provide the best possible information to allow for accurate repair and excavation decisions.
Like other major metropolitan areas, the City of Montréal has aging pipeline infrastructure that runs through its downtown core. In Montréal – one of the oldest cities in North America – this infrastructure is very old and beginning to reach the end of its design life. In order to proactively identify problem areas in its Prestressed Concrete Cylinder Pipe (PCCP) assets, the City is in the midst of an inspection program using advanced non-destructive technologies. In total, the City will assess the condition of over 40 kilometers of PCCP by 2015.
In the majority of cases, assessing the condition of assets to identify problem areas has high value for utilities, since the majority of pipelines have remaining useful life, despite their age. This allows for selective rehabilitation in favour of full-scale replacement. This is particularly important in urban areas, since excavation costs are higher and more disruptive in urban environments.
For a large portion of the condition assessment, the City is using the PureRobotics™ platform, since it is ideal for challenging urban environments. The tool remains tethered to the surface during inspection and is controlled by an operator. It also features live high definition video to observe internal pipe conditions. These features allow the City to see internal pipe conditions and closely verify areas with potential problems.
In addition, the tool identifies broken prestressing wire wraps in PCCP. As PCCP ages, the prestressing wires, which make up the main structural component, begin to break due to a number of factors.
The presence of broken wires in PCCP is the main indication that the pipe will eventually fail. Unlike metallic pipe materials that typically fail after a long period of leakage, PCCP is prone to sudden failures when too many wires break in one area. The diagram below demonstrates how PCCP typically fails.
Recently, the City has completed the assessment of just over 17 kilometers of its urban PCCP assets with diameters of 600, 750 and 900 millimeters (24, 30 and 36 inches). Of the 2,798 pipe sections assessed in this 17 kilometers, only 97, or 3.5 percent, have shown evidence of distress. This is slightly below the industry average of 5 percent of pipe sections with distress.
Using condition assessment, the City has been able to identify isolated distress on its critical urban mains, while leaving pipeline assets with remaining useful life in operation.
After completing the initial phases of condition assessment, the City has excavated certain sections of pipe for validation of the inspection results, as well as repair of any damage.
Both the excavation locations and presence of distress have been very accurate. This has allowed the City to repair isolated pipe sections, which restores the overall condition of the pipeline. This will help to prevent failures that would significantly disrupt day-to-day life in the city.
In addition, the City now has a baseline condition of all of the assessed pipelines, which helps in the development of future capital planning for monitoring or re-inspection.
By proactively assessing its PCCP mains, the City of Montréal is taking steps to prevent pipe failures, while allowing for more fiscally responsible asset management in the future.
PureRobotics uses powerful modular robotic pipeline inspection systems that can be configured to inspect virtually any pipe application 12-inches (30.5 centimeters) and larger.
Pure Technologies is helping utilities manage their buried infrastructure through its Assess & Address which can often be implemented for only a fraction of the capital replacement cost.
While evaluating wire breaks are an important part of PCCP management, it is important to acknowledge additional factors beyond wire breaks. By acknowledging additional condition factors, limitations of wire break assessment, and considering other rehabilitation approaches, there may be a more sustainable PCCP management approach (or combination of approaches).