By Tex Enoch, Induron Water Tank Market Manager
Water and Wastes Digest recently published an article by Tony Stellema entitled, “The Proof is in the Coating.” The article discusses why a quality coating application on a steel storage tank is vital to the tank’s durability.
Stellema touched on many of the points that are important in selecting the proper coating system for protecting steel tanks:
- Choosing the correct system to handle the contained liquid
- Proper surface preparation and inspection
- Methods of holiday detection
Most of what Stellema discussed could better be applied to shop-applied coatings on shop-built tanks or tanks that are powder coated or glass lined, rather than coatings and coatings systems that are applied to welded steel or field-erected tanks. He did discuss shop blasting and priming, and his point about making sure the prime coat is applied over steel that has been properly prepared BEFORE flash rusting occurs is well taken.
The Society for Protective Coatings (SSPC), the National Association of Corrosion Engineers (NACE), the American Water Works Association (AWWA) and the Steel Tank Institute /Steel Plate Fabricators Association (STI/SPFA) have all worked together to develop surface preparation, coating and application standards that apply primarily to field-erected steel WATER tanks, but which also can be modified for tanks containing waste water and many other liquids. These tanks all receive liquid-applied coating systems, both on the interior and exterior. Often they are shop primed, and the balance of the system is applied in the field, after the erection process is completed.
AWWA D102, “Coating Steel Water Storage Tanks,” is revised every five years. This standard lists the systems approved for use on the interior and exterior of steel water storage tanks. It is a comprehensive document that enumerates these approved systems, but also discusses, among other topics:
- proper surface preparation for the various systems
- information that must be supplied by the coating manufacturer
- system application
- safety precautions
- inspection and testing requirements
- first anniversary inspection requirements
- proper treatment of the underside of flat bottom tanks
- inside dry areas coating systems for elevated tanks
- cathodic protection
Currently there are seven exterior systems and five interior systems listed in this standard. All interior systems submitted by manufacturers must be certified for contact with potable water in accordance with standards established by NSF ANSI 61.
Clean air and water regulations, coupled with increasingly stringent V.O.C. requirements have resulted in coatings that have a much higher volume-to-solids ratio. These higher-solids products require cleaner surfaces with better-defined minimum surface profiles. Often times, shorter re-coat windows and more sophisticated application equipment are required. All this is discussed in AWWA D-102.
STI/SPFA conducts Steel Water Tank Seminars in different cities four or five times a year. The entire tank building process is discussed. These include:
- applicable standards
- the selection, sizing and location of a tank
- the fabrication and erection procedures
- cathodic protection
- surface preparation and painting
- installation of cellular antennae
- future maintenance requirements
It is very thorough, and each module is presented by an industry expert in that particular field. There is also a module on the total cost of ownership whereby the total lifetime cost of a steel tank is compared to a similar sized concrete and bolted steel tank. The TCO module and the modules on standards, fabrication and erection and the painting process are all offered online by STI/SPFA by visiting their website at www.steeltank.com.
In short, there are many resources available to those of us in the steel tank marketplace. With proper system selection, the correct surface preparation and application procedures, coupled with good inspection, steel tanks will not need future maintenance for at least 20 years and with a proper maintenance program they will last indefinitely.