Corrosion resistance: Desert-bound chemical and potable-water tanks

RL Industries (Fairfield, Ohio) recently overcame logistical obstacles to successfully fabricate five large composite storage tanks for a chemical plant in Saudi Arabia. The contract called for three 20-ft/6.1m diameter chemical storage tanks for the project; one is 47.7-ft/14.5m high and two are 41.3-ft/12.6m high. The tanks were design-engineered for 8 inches (+20 mbarg) positive pressure and 1.2 inches of water (10 mbarg) negative pressure at a design temperature of 194°F/90°C. RL Industries also had to construct two 7-ft/2.1m diameter by 16-ft/4.9m high tanks for holding nonpotable water for emergency safety showers. To keep ambient Saudi temperatures from making the water too hot, these tanks were designed with 2 inches/5 cm of sprayed urethane foam insulation encapsulated within the laminate.

To avoid any issues of contamination of the composite laminate and to provide better control process parameters, the company opted to manufacture the tanks in sections at its Ohio facility, rather than construct an onsite manufacturing cell. In addition, the company’s facility and processes are certified to demanding American Society of Mechanical Engineers (ASME) standards for corrosion-resistant structures.

To resist the highly acidic 32 percent solution of hydrogen chloride or 20 percent solution of sodium hydroxide that the tanks would contain in service, the company selected trademarked Vipel F010 bisphenol A epoxy vinyl ester resin from AOC Resins (Collierville, Tenn.). The tanks were filament wound in sections, using Vipel resin and fiberglass, after first laying down a corrosion barrier of chopped glass strand mat (CSM) and two plies of carbon fiber veil, also wet out with Vipel. Openings and attachment features for ladders and rails were integrated into the wound sections. The top and bottom domes were vacuum infused with fiberglass reinforcements and structural sandwich core. RL Industries designed the bottom-end closure with an integral, high-strength “knuckle radius” for greater strength at the transition between the tank cylinder and the end cap or dome.

The finished tank sections were trucked to an assembly site 20 miles away and sequentially assembled using a wet laminating technique similar to that used to join chimney liner “can” sections. After the tanks successfully passed hydro-testing protocols, they were barged down the Ohio and Mississippi Rivers to a Gulf of Mexico port and transferred to a ship bound for Saudi Arabia.