Controlling Corrosion and Preserving Water Quality

Authors:

  • Becki Rosenfeldt, P.E. - Hazen and Sawyer

Flow-through pipe rack system with five parallel loops of copper, lead, and lead-soldered copper pipes.

Corrosion coupons

In an effort to comply with drinking water regulations such as the USEPA Stage 1 and Stage 2 D/DBP rule, an increasing number of drinking water providers are altering their treatment systems’ processes, resulting in changes to finished water quality. Concurrent with changes in finished water quality has been an increase in lead corrosion in some drinking water systems. Hazen and Sawyer has taken a practical approach to evaluating the corrosive effects of finished water quality changes, performing targeted testing from desktop/benchscale to flow-through pilot loop and full-scale studies to help utilities make educated decisions with regard to treatment process alterations and distribution materials.

Drinking water utilities today face a number of issues related to corrosion of distribution system materials including:

• Aging distribution infrastructure and premature failure of newer equipment due to the accelerated corrosion of materials.
• Compliance with Lead and Copper Rule revisions.
• Compliance with Stage 1 and Stage 2 Disinfectant/Disinfection By-product Rule.
• Declining water use for some utilities, leading to increasing detention times, water age, and opportunity for corrosion, which can negatively impact water quality.

Traditionally, the evaluation of corrosion has been done with the calculation of industry-accepted indices, performing pilot loop or coupon studies, or the evaluation of full-scale system samples. Hazen and Sawyer has demonstrated success using both desktop and pilot studies to evaluate the corrosive effects of finished water quality changes. Constructing customized pipe racks with several parallel loops allows us to test several corrosion control schemes or several different treated waters simultaneously (and/or allow for duplicates to increase data reliability).

The test apparatus facilitates evaluation of both general corrosion rates and comparative first draw stagnation samples side-by-side, enabling us to study the effects of water quality changes on the corrosion of household plumbing (lead soldered copper pipe), as well as a full range of distribution system materials such as cast iron, steel, brass, and bronze.

Among other similar projects, Hazen and Sawyer is currently studying the use of an alternative corrosion inhibitor that may provide significant cost savings from both a reduced application of inhibitor and a reduction in caustic soda dose. An extensive pilot test using lead, steel, and copper coupons, as well as lead soldered copper pipe, is underway to evaluate the relative effectiveness of this inhibitor compared to the current use of phosphoric acid as an inhibitor.

Other recent work in this area includes:

• A detailed evaluation of the effects of converting to chloramine treatment on corrosion of lead, copper, and brass for New York City and for several smaller utilities.
• Assisting an upstate New York water system with corrosion issues that occurred after its wholesale sup supplier switched to chloramines and the main industrial user greatly decreased water demands.
• Addressing unique corrosion control issues on the cruise ships.
• Assisting a mid-Atlantic client with solving red water complaints.
• Examining the effect of switching coagulants to improve TOC removal on corrosion control for several utilities.

The USEPA recently declared corrosion as a “key area of research” in their effort to maintain high-quality drinking water throughout distribution systems. In addition to its impact on water quality, corrosion also represents a substantial economic expense for utilities today. By studying the effects of subtle water quality changes at a remote location, we can provide informed recommendations with regard to lead and copper corrosion and inhibitor or water quality changes that may be needed to comply with newer rules, reduce potential capital and operating expenses, and protect public health.

This article is taken from the Spring/Summer 2010 Horizons.

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