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Battling the enemy

Battling the enemy

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    Crews at the Central Costa Sanitary District Wastewater Treatment Plant install deep-well anodes for a cathodic protection system designed to protect the secondary-treated-effluent welded steel pipe (shown with a white coating at the rear of the photo). The deep well was drilled to a depth of 320 feet and was about 12 inches in diameter. Photos: V&A Consulting Engineers Inc.

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    Left: Welders connect paired cathodic protection wires to below-grade wastewater pipes. Only a small fraction of U.S. wastewater systems are currently provided with cathodic protection. Right: Polyvinyl chloride sheeting—shown here in interior-wall form—will protect the new pump station from sulfide-induced corrosion.

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    Atmospheric conditions caused corrosion on this flexible coupling.

Repainting the Picture

For the wastewater industry, the most important development in the past decade is not the technology or materials, but broader acceptance of these materials by the marketplace. The first generation sometimes failed prematurely or had a shorter-than-promised useful life. Many suppliers also folded, so users had no recourse in case of failure. In addition, there was little in the way of industry-wide coordination or standardized specifications and designations.

Today's coatings and linings industry, in contrast, has gone through an extensive shake-out and consolidation. There are far fewer suppliers, but those remaining have passed the test of time, and their products are more reliable than ever. As a result, more new facilities incorporate nonmetallic, nonreactive, and relatively maintenance-free fiberglass for piping, I-beams and channels, plates, pipe supports, and other components. The most heartening development is that corrosion is no longer a “below-the-radar” issue. We see this in the growing number of corrosion-prevention symposia.

The majority of corrosion problems in wastewater plants could be eliminated by adhering to two simple guidelines:

  • Someone must review plans and specifications of any new treatment plant with an eye toward corrosion mitigation. If potential weaknesses are flagged right away (such as copper fittings in a high-sulfide atmosphere, dissimilar metals in contact or near proximity, areas of concrete exposure to H2S and sulfuric acid), appropriate modifications or changes can be made.
  • Agencies need to extend their time horizon and think in terms of an indefinite life for major assets. Unfortunately, few agencies can afford their own corrosion experts, and asking facility owners to increase the frequency of inspections when everyone is being asked to do more with less may sound quixotic. It is understandable that corrosion protection often takes a back seat to other, more pressing issues—until a catastrophic failure; then, it is all too clear that deciding 20 years ago to save $50,000 on corrosion protection is the reason we are spending millions today on emergency repairs.
  • One of the landmarks in my corner of the world is the Golden Gate Bridge—a celebrated engineering feat, and also a highly visible role model for how to properly maintain a structure. The Bridge Division—part of the Golden Gate Bridge, Highway, and Transportation District—employs a team of engineers and ironworkers for regular inspection and minor fixes, while a crew of 28 bridge painters continually works to guard against corrosion. The result has been 68 years of continuous service without a single corrosion-induced emergency, despite an aggressive marine environment. We expect the Golden Gate to continue to reliably serve future generations.

    Wastewater treatment plants and sewer mains may not have the charisma of a world-famed landmark bridge, but they are equally vital, severe-service, “24/7/365” infrastructure assets, and a failure could have severe economic and public-health impacts. Given the same kind of attention and occasional, minor “touching-up”—once every five years would be enough, in most cases—there is no reason these facilities, too, shouldn't enjoy a similarly trouble-free, virtually unlimited service life.

    Villalobos is president of Oakland, Calif.-based V&A Consulting Engineers Inc.