March 24, 2009

Choosing Exterior Tank Coating Systems

by Tony Ippoliti

steel-tankWhen considering a welded steel water storage tank, professional and consulting engineers know that, with proper maintenance, the tank has an indefinite life span.  But they often ask: “what paint system should I use on my new water tank?” and “How long will it last?”  Since very few, if any, civil or environmental engineering courses include lectures about paint coatings, where can you get the decision-making information you need?

Paint coatings are changing because of regulatory influences, and coating specifications that you may have used for a water tank project even a few years ago may be outdated and not be appropriate today. Some coatings may not be available, for example, because they are no longer VOC compliant.

You can find an estimate on how long a coating system may last by contacting NACE International and purchasing Paper No. 06318, which was presented in 2006 at the NACExpo. This paper is entitled “Expected Service Life and Cost Considerations for Maintenance and New Construction Protective Coatings Work” and in it, you’ll find several different coating systems and methods of surface preparation to help you determine which system to use and how long it should last. You can even find the effect that the environment (rural vs. industrial) has on paint coating performance.

Individuals from 40 companies assisted in the creation of Paper No. 06318 and “service life” is defined as the time until 5 to 10% coating breakdown (rusting) occurs.

Suppose, for example, a paint coating representative asks you to consider a zinc-rich primer instead of a “traditional” epoxy primer on a new tank project.  If you apply an intermediate coat of epoxy and a topcoat of urethane, you may ask: “what benefit is derived from changing to a zinc-rich primer?” You’ll discover that the difference may be as great as 9 additional years of service life simply by making the primer change.

What more would you like to know about coating systems for the exteriors of water tanks?

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