By Michiel P.H. Brongers
Water Condition & Purification
A recent study estimated the corrosion-related costs for the U.S. drinking water sector are $22.25 billion annually. No other U.S. industry sustains a larger amount. These costs include spending to replace and/or rehabilitate deteriorating systems; corrosion treatments such as addition of corrosion inhibitors, pH adjusters and alkalinity control; internal linings, external coatings and cathodic protection, and unaccounted water leaking from drinking water systems.
The cost of corrosion to consumers is enormous and increases as underground systems suffer from internal and external corrosion attack. As the nation's systems expand and more metallic distribution piping is buried, this asset will begin to deteriorate out of sight due to corrosion and age.
To realize savings from reduced costs of corrosion, changes are required in three areas - policy and management framework, science and technology, and technology transfer and implementation. The policy and management framework is crucial because it governs identification of priorities, allocation of resources for technology development and system operation.
Threat to pipelines
The nation's drinking water system includes about 880,000 miles of underground pipelines and supplies between 125 and 175 gallons per capita per day (gpcd). This valuable asset is subject to both internal and external corrosion, resulting in pipe leaks and water main breaks. Water quality and quantity are affected by leaks and ruptures. Likewise, water quality can be affected by corrosion as it affects internal surfaces of the distribution system. Consumers may notice their drinking water smelling bad; red or yellow water may come from their faucets, or houses may suffer damage from corrosion leaks in residential water piping.
Previous studies have shown deterioration by corrosion is a large problem. In March, 2000, the Water Infrastructure Network (WIN) estimated the current annual cost for new investments, maintenance, operation and financing of the national drinking water system at $38.5 billion per year. WIN stated that the current spending levels are insufficient to prevent large failure rates in the next 20 years. The WIN report was presented in response to a 1998 study by the American Water Works Association (AWWA) and a 1997 study by the U.S. Environmental Protection Agency (USEPA). Those studies also identified the need for major investments to maintain the aging water infrastructure.
In addition to the costs of replacing older infrastructure, there's the cost of unaccounted water. One city reported a 20 percent loss of unaccounted water annually over 25 years, with 89 percent of main breaks directly related to corrosion. Nationally, it's estimated about 15 percent of treated water is lost. Treatment of water that never reaches the consumer results in inflated prices (estimated at $3 billion per year) and over-capacity in treatment facilities. Justification for investments in piping replacement or rehabilitation can be found by performing a cost/benefit analysis on a per-system basis. In a cost/benefit analysis, the benefits of reduced leaks and maintenance are balanced against the costs of a specific waterline construction project.
Policy and management
A major barrier to progress in corrosion management is the absence of a national information system on all water systems. Restricted communication between water utilities limits the awareness and implementation of available corrosion control technologies such as new coating systems and cathodic protection (CP). Moreover, the lack of information complicates the process of prioritizing maintenance. AWWA maintains partial records on water systems of its members and the USEPA collects data from voluntary questionnaires, however, most water utilities don't have complete records on all of their underground pipes. Pipe mileage length, pipe materials, pipe diameters and their installation dates are, in many cases, unknown. At the local level, corrosion engineers maintain small databases with information on the nature of individual repairs, but often these records aren't integrated into a larger data system. Current estimates for pipe replacement rates range from as low as 0.46 percent to 5.0 percent per year. Utilities should gather relevant data to determine pipe replacement rates because it helps in planning and budgeting for system maintenance. Improved modeling of pipe replacement would allow statistical analysis and predictive assessments for system performance. Computers provide the opportunity to maintain these records both in local and national databases.
New developments in electronic equipment make internal inspection with cameras and/or sensors an option to evaluate the condition of pipe sections. These techniques, however, are currently not commonly used because they're still quite expensive, equipment insertion and extraction from the pipe is usually difficult, and the pipe may have internal obstructions or bends. In addition, analysis of the data is generally time-consuming and difficult.
Science and technology
While corrosion management has improved over several decades, the United States is still far from implementing optimal corrosion control practices. There are significant barriers to both development of advanced technologies for corrosion control and implementation of those technological advances. A major challenge involves disseminating corrosion awareness and expertise that's currently scattered throughout government and industry organizations. In fact, there's no focal point for effective development, articulation and delivery of corrosion cost-saving programs.
Water transmission and distribution systems can be protected from internal corrosion by using corrosion inhibitors in combination with pH adjusters and alkalinity control. A second method of internal corrosion protection is the application of a cement mortar lining to iron-based pipes. External corrosion protection can be obtained from coatings and CP.
New iron and steel pipelines are commonly lined with cement mortar. Cement mortar linings are also used for rehabilitation of older ductile iron, cast iron and steel water pipeline networks. The linings can eliminate small leaks in pipes and pipe connections as a result of the high resistance of cement mortar to pressure and enhance the hydraulic characteristics of piping by preventing internal corrosion products from forming and possibly restricting water flow. Studies by AWWA show the cost for water pipe rehabilitation by cement mortar lining ranges from 13 to 41 percent of the total costs of total pipe replacement.
The direct cost of maintenance and repair of water pipes and repaving after work is about 50 percent of the total budget of water departments. Repairs can be minimized if control methods are applied to the system. External corrosion can be effectively controlled. Although these corrosion control methods have problems of their own, the initial cost for installing coatings and CP on new systems is almost always warranted because large maintenance cost savings can be achieved over the life of the piping system.
Technology transfer and implementation
A third barrier to progress in corrosion management is lack of understanding and awareness of corrosion problems at the local level, and limited time dedicated to solving corrosion problems. Often, an attitude is taken of burying the water pipe and forgetting about it until it fails. Investigations of corrosion-related parameters in drinking water are an important aid to water utilities. The data should be used to regularly reevaluate applied chemical treatment for internal corrosion protection. External corrosion protection can be evaluated by systematic inspection of coating and CP systems at regular intervals. Maintenance crew can be educated to perform visual inspections of coatings during excavations and to monitor or spot-check CP systems to make sure they're properly energized.
It was found that most utilities maintain detailed information about their local system; however nationally the system information isn't integrated. A national water system database could include data on unaccounted water and improved communication between departments and individuals utilities. In addition, corrosion knowledge could be more easily compared if coupled information would be available in a generally used format, and the assessment of the effectiveness of different corrosion control approaches could be improved.
Conclusion
Underground drinking water pipes age both from internal and external corrosion attack. The cost of corrosion to consumers is estimated at $22.25 billion annually. This great cost grows as systems age. The asset of metallic distribution piping is buried, resulting in a hidden problem of deterioration by corrosion. To reduce the impact of corrosion and realize the savings from reduced related costs, a national strategy should be formulated based on the above discussion.