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Coating Fundamentals: Above Ground Steel Tanks

Coatings are essential to ensure steel tank longevity. When the application is done right the first time, it saves time and money. But, coatings failure can and do occur for a variety of reasons. Which is why it is paramount to determine the root cause of the problem and to determine how to fix it. Tank coatings fail due to insufficient surface preparation, poor application, a defective coating, or an inadequate specification. Also, if the information is available, the history of the coating used, weather during application, and application procedure will help to prevent future failures.
Below is a breakdown of the most common reasons for coatings failure.
Not Selecting the Proper Coating Materials
The saying, “you get what you pay for”, can be applied to tank coatings. The quality of materials used can affect the longevity and any long-term maintenance. When inexpensive materials are used to offset high labor costs, the quality can suffer greatly. In the end, project managers end up paying more to repair the coating. But, using the most expensive materials may also not be the best route to coat a tank. Project managers need to choose the right materials, tools, and equipment for their tanks before they see a high return on their investment.
But choosing the right resources is also dependent on a few conditions:

  • Humidity and temperature
  • Presence of UV radiation (coatings, such as epoxies, will deteriorate by chalking when exposed to sunlight)
  • Chemical exposure (exposures may include acidic or alkaline concentrations, industrial smog, acid rain, or sewage
  • Mechanical damage

Environmental corrosion (the harsher the weather conditions, the more thorough surface preparation has to be):

  • the type of coating used for protection
  • the total thickness of a coating system
  • the surface preparation required
  • minimum and maximum inspection and repair or recoating intervals

Not Ensuring Proper Surface Preparation
Most surfaces require a base protection coat to keep them from corroding in aggressive environments. But inadequate surface preparation can affect the coating adhesion, which reduces the projects’ lifespan. Also, if any surface contamination is present, such as chemicals, loose paint, sharp edges, rust, or mold, it disables bonding to the adhering paint.
And during the coating application, make sure the methods meet the manufacturer’s requirements. Also check for ideal temperature and humidity levels during curing period.
Not Performing Proper Inspection
Another method to ensure coatings longevity is proper inspection and maintenance. Inspect painted areas, clean surfaces to remove any debris or chemicals, and frequent highly corrosive areas, such as those subjected to frequent chemical spillage and corrosive fumes. Areas exposed to less severe conditions, such as interiors and exteriors of potable tanks need annual inspection to assess the condition of the coating system.
Also, inspectors need to check all materials that arrive for coating applications to make sure they are in good working condition before use. Make sure to also keep all work documents to avoid any surprises, and inspect that work procedures are carried out safely.
Although, most coating failures are easy to identify and prevent, other elements that are equally important, are common sense, experience, and experimental observation.

TNphoto Tatsuya Nakagawa
Tatsuya Nakagawa is the VP of Marketing and co-founder of Castagra Products, a storage tank and wastewater coatings manufacturing company that is highly acclaimed for its sustainable coatings and cold weather coating applications. Castagra products are NSF-61 certified and are used by the world’s top water and wastewater contractors.