Figure 1:Water main failure rates as a function of material type -- asbestos cement (AC), cast iron (CI), concrete steel cylinder (CSC), ductile iron (DI), polyvinyl chloride (PVC), steel, and other.
The study also discusses how water main failure rates for CI and AC pipes could increase exponentially over time. “One could envision a rapid increase in break rates in the near future for cast iron and asbestos cement pipes. Utilities across the country would need to rapidly ac- celerate their pipe replacement schedules to avoid potentially serious economic and social impacts. If a break rate doubles, the economic impact is significant; one would need to double the number of person- nel repairing failures along with supplies and materials while loss of treated water increases. Societal impacts would be devastating if the break rates reached exponential levels,” Folkman said. A critical new finding is that smaller municipal utilities have twice the water main break rates as larger utilities. “With less revenues and re- sources, smaller municipalities will need to use the most cost-effective and durable pipe materials available to address pipe renewal and re- habilitation requirements. Larger municipal utilities, however, are not faring much better, since the rate at which they are replacing the pipes that are now beyond their useful lives is inadequate,” Folkman said. According to the survey, an average of 0.8 percent of installed pipe is replaced each year across the country. This equates to a 125-year national pipe replacement schedule. Pipe replacement rates should be between 1 percent and 1.6 percent, equivalent to 100-year and 60-year replacement schedules, respectively. In general, pipe replacement rates need to increase. A reconfirmed major finding is that polyvinyl chloride (PVC) pipe has the lowest overall break rate when compared to cast iron, ductile iron, concrete, steel, and asbestos cement pipes (see Figure 1). PVC was also the pipe material with the lowest break rate in USU’s 2012 study. Corrosion can be a major cause of water main breaks, with 75 percent of all utilities reporting corrosive soil conditions. This study has shown that cast iron pipe in a high-corrosion soil has more than 20 times the break rate than one in a low-corrosion environment. Similarly, ductile iron pipe in a high-corrosion soil has over 10 times the break rate than one in a low-corrosion soil. Other national benchmark findings include: • nationwide, one mile of installed water main serves 308 people; • 85 percent of water pipes are less than 12 inches in diameter;
• the percentage of water mains over 50 years old has increased from 22 percent to 28 percent in the last six years; • pipe material usage varies significantly over geographic regions, sug- gesting pipe selection and use is based on historical preference versus comparative cost analysis or environmental conditions; • since 2012, the percentage of installed water mains that are beyond their useful lives has doubled from 8 percent to 16 percent; • CI pipes represent the largest pipe material inventory and 82 percent of all CI pipes are over 50 years old; • construction-related failures were equivalent for both PVC and ductile iron pipes, pointing to the need to improve construction practices for underground infrastructure regarding installation, location services, and inspection; • conservation benchmarks include a national drop in average supply pressure to 69 psi (from 77 psi in 2012), which is well below the maxi- mum operating pressure of water mains, extending pipe life as well as reducing leaks and breaks; • average gallons per day per person is 137, which suggests successful water conservation efforts across the country; and • estimated average water loss due to leakage is 10 percent, showing that pressure reduction, leak detection, and pipe replacement have contributed to reducing water loss in water distribution systems. This comprehensive study contributes to the continuing efforts of the EPA’s Aging Water Infrastructure research, Virginia Tech’s Sustainable Water Infrastructure Management Program, the U.S. Conference of Mayors’ Water Council, and the asset management and water infra- structure condition assessment efforts of the American Water Works Association (AWWA) and American Society of Civil Engineers. Folkman is a member of the AWWA and a member of the Transporta- tion Research Board Committee on Subsurface Soil-Structure Interac- tion. He has oversight of USU’s Buried Structures Laboratory. View the report, including the full set of key findings and its methodol- ogy, at https://digitalcommons.usu.edu/mae_facpub/174.
Information provided by Utah State University (www.usu.edu).
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may 2018
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