by Lori Riddle
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Water Storage Tank - FIsher Tank COmpany and TnemecThis week we welcome Andrew Rogers of Tnemec to the Think Tank. Andrew shares a water storage tank case study that shows what happens when the right tank meets the right coating system.

Fisher and Tnemec Stand The Test Of Time

Ground storage tanks, at some point, can fall victim to corrosion; it’s the nature of the beast. Selecting the right tank for your refinery, power station, terminal, industrial site, or water system, can make a world of difference and picking the proper design and maintenance cycle prior to construction can show benefits long after the tank has been put into service. Fisher’s goal in new construction is to fight corrosion before it begins, which has proven to be more cost-effective than dealing with the problem after construction. Need proof?

In 1998, Brentwood Water Company needed to build a tank in Morganton, N.C., and they decided on a Fisher-designed welded standpipe. Now, after 15 years of service, the tank is still in prime condition because of choices made before the construction process.

The tank itself is a major factor in the standpipe’s longevity. When evaluating the cost of all tank types, including bolted or welded steel or concrete, welded steel tanks have a lower total cost of ownership when properly maintained. Because of this, Brentwood chose a welded steel tank, with seal welding on an umbrella roof, and understood the benefit this choice could make down the road. They also understood that the interior and exterior coatings system they chose to protect the tank’s steel would contribute to the tank’s lifetime, so Fisher assisted them in specifying the best available system for the job.

Before a coating system can even be applied, the steel must be prepared in accordance with surface preparation standards to provide an angular profile and to create a greater surface area, helping the coating’s ability to adhere. In the case of the Morganton tank, the interior steel was prepared in accordance with SSPC-SP10/NACE No. 2 Near-White Blast Cleaning, while the exterior of the steel was prepared to meet standard SSPC-SP6/NACE No. 3 Commercial Blast Cleaning. Even though this was a newly constructed tank, and there were no old coatings or excess rust of major concern, this preparation helped ensure optimum adhesion of the prime coat and reduce the chance of surface contamination.

The coating systems chosen for the Brentwood standpipe were manufactured by Tnemec – an industry leader in coatings for the storage tank market. The best coatings available were applied, including a two-coat epoxy system for the interior steel and an epoxy/urethane system for the exterior. Selecting coatings, like selecting tanks, can determine the life cycle of the infrastructure and the system chosen for this tank was top-of-the-line when specified.

Interior steel received a prime coat of Tnemec’s Series 20 Pota-Pox, an industry standard polyamide epoxy known for its benchmark performance in varied conditions. Because this coating would be in direct contact with potable water, it had to conform to AWWA D 102 and be certified by NSF International in accordance with ANSI/NSF Std. 61. Series 20 Pota-Pox not only follows these requirements, but because this epoxy can be used in immersion service and dry service, it was applied to the entire interior of the tank. The same product was applied again as a finish coat once all welded metal and rough areas were painted with a stripe coat.

The exterior of the tank received a prime coat of Series 66 Hi-Build Epoxoline, a self-priming, forgiving epoxy that can be applied in a thick coat for protection of exterior steel. This coating has been applied on thousands of tanks and architectural structures over the last 30 years with incredible results.  After another intermediate coat of Series 66 was applied, a coat of Series 1074 Endura-Shield was applied as the tank’s finish coat, an aliphatic acrylic polyurethane highly resistant to exterior weathering. Although more advanced topcoat technology has been developed in recent years, this coating has retained its integrity and color while protecting the exterior steel from the many penetrating factors like UV rays and ever-changing weather.  

Water tank interior maintenanceNow, fifteen years after this 248,000 gallon tank was erected and put into service, it is in excellent shape. Although minor mildew growth has begun around the base of the standpipe, there appears to be no rust outside of the normal bleed lines seen on the inside of water tanks in service. Recently evaluated by Tnemec coating consultants, the tank will not require a full recoat – contrary to claims stating welded tanks need full recoating every fifteen years – and still has several years before it even needs an overcoat.

The tank’s design, especially the welded steel, umbrella roof, and the coatings system applied, were construction choices that paid long-term dividends. Even without a zinc-rich primer – which has now become a standard water tank coating – or an ultra-durable glossy fluoropolymer topcoat, the tank has fought aging and corrosion. And, because this system can be over-coated, when Brentwood needs to perform maintenance on this tank a few years from now, they will be able to upgrade to another high performance coatings system.

Visit Tnemec for more information about how advanced coatings systems can add value to your tank.

Stop by and see us at FisherTank.com for more information about field erected welded steel storage tanks!

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