ABSTRACT

Internal corrosion of water distribution piping is often difficult to detect, diagnose, and mitigate, especially if the problems are localized. Corrosion can cause leaks, premature piping failures, and poor water quality in water distribution systems. New commercially available in-situ sensors can detect active corrosion and/or corrosive water and can notify facilities engineers that there is a problem. A new field demonstration of these sensors will be described in this paper.

Computer-based simulations of water distribution systems can also be used as a diagnostic tool to help solve corrosion problems. Simulations can help pinpoint areas in which localized hydraulic and/or water quality conditions are contributing to internal piping corrosion. An example will be presented in which an off-line dynamic simulation was used to help locate and diagnose a series of localized corrosion problems in an actual water distribution system.

Finally, the above sensors and simulations can be interfaced together with Supervisory Control and Data Acquisition (SCADA) systems to provide a highly accurate, near-real-time description of water system operation. Such a system can be used to automatically control the dosing of water treatment chemicals so that corrosion is mitigated.

INTRODUCTION

Water distribution systems and water storage tanks should have a service life of 50 to 75 years. However, severe general and/or localized corrosion can shorten the service life to as little as 20 years due to leaks. A corroded and leaking water distribution system typically loses 20 to 25% of the water it conveys. Severe internal corrosion of unlined steel, cast iron, or ductile iron pipes usually results in poor water quality for occupants?water containing dissolved corrosion products (rust) is frequently discolored and may have an unpleasant taste and/or odor. In some cases the water may exceed the maximum contaminant level for iron of 0.3 mg/l as specified in the Environmental Protection Agency?s National Secondary Drinking Water Regulations. Water quality problems may become so severe that residents are forced to use expensive bottled water for drinking and cooking. The worst case is an unexpected catastrophic failure that occurs when the piping system is under stress due to high usage or environmental conditions, such as during firefighting or severely cold weather. Failure of a critical water main during a firefighting situation can result in loss of lives and property.

The first line of defense against internal water piping corrosion is an effective water treatment program. However, the quality of water tends to degrade as it travels from the treatment plant to the consumer. Water that stays in the distribution system for many hours or days can become corrosive and/or stagnant as the corrosion inhibitors and disinfectants are consumed. Water system hydraulics (flow rates, consumer demands, pressures) controls the amount of time the water remains in the distribution system. Piping and consumers that are located far away from the treatment plant or that are located in areas where water consumption is low may receive water that is very different from the high quality water that leaves the plant. Localized corrosion problems can occur in these remote and/or low usage areas.

Another related cause of internal water piping corrosion problems is inconsistent water quality over time. Inconsistent water quality prevents pipes from forming the protective oxide films that inhibit corrosion. Systems that obtain water from multiple sources (often for security and reliability reasons) are especially vulnerable to this problem.

Before action can be taken to correct remote and/or

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