Storage tanks for oil and liquids associated with the booming fracking industry dot the landscape, particularly in Texas, Oklahoma and Colorado. Traditionally, they have been protected with conventional epoxy and urethane coatings, which have served their purpose to a point as the advances in fracking have shown their protective limitations with the sourer oils and corrosive frac mixtures.
Demand has grown for greater protective qualities and not only for the tanks themselves but also for the environment and the workers who apply the coatings — in short “green” coatings with the lowest possible toxicity. Volatile organic compounds (VOCs), aside from their potentially toxic qualities, make the application of conventional coatings extremely unpleasant for anyone within close proximity and can necessitate closure of adjacent work space.
A new generation of plasticized vegetable oil-based coatings have eliminated VOCs and, because of their high gypsum content of 60-70 percent approximately, have an exceptionally high fire-retardant rating as water vapor is emitted under heat from fires. The plasticized vegetable oil coating is completely nontoxic and can be used in direct content with potable water as it has an ANSI/NSF 61 rating.
Another aspect of the unique chemistry is the fact repair work over an indefinite period, and certainly the lifetime of the coating on a tank wall, recombines with the original coating, subject to it having been cleaned and dried prior to repair application. Nearly all coating jobs require some touch-ups or additional coating to areas considered highly vulnerable. In the case of conventional epoxy coatings, this can become highly problematical if not done immediately.
Two vital aspects of any coating are how well it grips the surface being coated and how much flexibility it retains.
Coatings are subjected to a number of factors that ultimately help destroy them. These include thermal and mechanical shocks, ultraviolet radiation and chemical content exposure. And even the best coating in the world will not protect a tank if the base it was sprayed or manually on was not properly prepared to the applicable NACE standard.
In the case of plasticized gypsum coatings, NACE 2, and in some cases NACE 3, is the minimally acceptable standard. Generally conventional coatings, because of their comparably more fragile characteristics, require even higher standards if they are not to fail rapidly in harsh shock environments.
Plasticized gypsum coatings have survived over 20 years on ship decks where conventional epoxy coatings have demonstrated micro-cracking failures along deck welds within months of application. The marine coating had a lengthy testing program. In April 1991, a test block was prepared and over a 20-year period shore D Hardness values remained unchanged at approximately Shore D50. Similarly, shavings from slices of the test slug revealed no significant change in flexibility over two decades.
Frac tanks vessels, especially those that are moved, are highly vulnerable to conventional coating failure because of the steel surface movement induced by radical temperature change and mechanical shocks associated with road and off-road transportation movement. Oil states have huge fluctuations in temperatures and North Dakota has particularly frigid winters. The 181 F (100 C) variation between North Dakota’s highest and lowest temperature is the third largest variation of any U.S. state.
The chemistry of the green coating also affords another advantage in the oil patch over conventional epoxies. It can be applied at temperatures well below those acceptable for conventional coatings. The main guideline for application of the veggie plastic coating is that the temperature of the target surface is a minimum of 5 degrees Fahrenheit above dew point, otherwise moisture can be trapped and cause bubbling.
In summary, even the best coatings in the world will be seriously compromised and fail early if the target surface to be coated is not prepared to the proper NACE standard. Surface preparation is paramount and there are no short cuts.
For more information, contact Tatsuya Nakagawa at (778) 322-0867 or tnakagawa@castagra.com.