Aging assets beginning to fail
Numerous sensational news stories about recent water pipe failures have many utility managers interested in assessing conditions of their water pipes and instituting an asset renewal program. There is a huge backlog of asset renewal work to be done, but limited financial resources to accomplish the work. As a result, utilities need a systematic approach to prioritizing inspection and renewal projects.
Establishing priorities
When deciding inspection and renewal priorities, many utility managers turn to their asset management program to determine where to spend their limited budgets. At the heart of a water pipe asset management program is an analysis of risk exposure, which includes two components: consequence of failure and probability of failure.
Consequence of failure relates to the damage and disruption customers experience as a result of a failure. In general, larger diameter water pipes have a higher negative consequence if the water pipe fails because they serve more customers. Reducing the consequence of failure of a given asset is often impractical or cost prohibitive.
Probability of failure relates to the condition of the water pipe and the likelihood of failure. The probability of failure is determined with a condition assessment. Generally, a new water pipe has a much lower probability of failure than a water main installed 100 years ago.
The graph below shows the results of a business risk exposure analysis for a New Hampshire seacoast community’s water distribution system. With this data, the community can begin to prioritize asset renewal projects. The goal of this analysis is to organize assets by risk exposure, and to evaluate the assets in the ‘high’ risk quadrant before tackling the asset replacement in the ‘medium’ and ‘low’ risk quadrants. How fast a community tackles projects depends on the tradeoffs between the desired level of service versus the desired level of asset renewal investment.
Condition assessment is a process that can be used by communities to further refine the likelihood of failure of a high risk water pipe before investing significant capital resources in this infrastructure.
Condition assessment of water pipes is similar to assessing wastewater force mains. Some of the issues with deteriorated water pipes include breakage, leakage, loss of hydraulic capacity and water quality concerns. One key difference between inspecting sanitary force mains and water pipes is that water pipes contain drinking water so any inspection technique needs to take into account how to perform the inspections without comprising the quality of the water. This includes disinfection techniques and testing for bacteria during or after inspection, both of which can add time and expense to the inspection procedure.
There is a wide range of non-destructive inspection techniques available for use in water pipe inspections.