Frac tanks are beneficial for a range of projects that involve storing liquid. They come in a variety of types, and choosing the right type of frac tank for the application is critical to project success as well as worker and environmental safety. Storing hazardous liquid in the wrong tank could lead to an industrial accident or an ecological disaster. When in doubt, your temporary equipment vendor can steer you to the tank that will serve you best.

What is a frac tank?

Frac tanks are large, mobile steel containers designed to temporarily store bulk quantities of liquids. These liquid storage tanks are often used in the construction, oil and gas and chemical manufacturing industries.

Frac tank types include open top frac tanks, closed top frac tanks, single wall frac tanks, double wall frac tanks and mini frac tanks. Most frac tanks have a flat bottom or a V-bottom for more complete draining and faster cleaning. Some frac tanks, such as mix tanks, are outfitted with electric motors and mixer paddles for storing materials that must be rolled or mixed.

Frac tank sizes

Frac tanks come in an array of sizes. One popular frac tank size has a storage capacity of 21,000 gallons (500 barrels). Mini frac tanks have a storage capacity ranging from about 7,000 gallons to 8,400 gallons. The choice of tank size depends not only on the amount of liquid to be stored but also on the amount of space available for the tank. Don’t forget to factor in any structures the tank will have to pass under or through on its way to the site location.

Some models of frac tanks have steel manifolds mounted to the front of the tank to allow several tanks be “manifolded” together. This attribute provides for the common connection of a battery of tanks that may be pumped in to or out of with a singular piping connection.

Matching the frac tank to the liquid

When choosing a frac tank, it’s essential to consider the characteristics of the liquid you’ll be storing to avoid an unwelcome and potentially dangerous outcome.

The pH

Acidic (low pH) liquids may require a different type of tank material or tank lining than basic (high pH) fluids. An acidic or caustic liquid can chemically attack the materials of construction of the frac tank. This can result in a leak or loss of containment from the frac tank. It is important that the chemistry that is to be stored in the tank be evaluated and matched with the correct elastomers and tank materials for the application.

The temperature

Many chemicals are more corrosive when heated. The frac tank construction materials, as well as the valve and gasket materials, must be able to withstand the liquid at the temperature it is expected to reach during storage.

The specific gravity

Most frac tanks are rated for storing liquids with a specific gravity of 1.7 to 2.0. (Specific gravity is the liquid’s density relative to water, which has a specific gravity of 1.) When storing high-density liquids you must consider the design parameters of the tank.

Open top vs. closed top frac tanks

Open top frac tanks are ideal for storing non-hazardous liquids such as wastewater, ground water remediation or storm water run-off. They are often used when treating these liquids prior to discharge.

Many of the products that are stored in frac tanks may off gas regulated vapors. This application typically requires a closed top vapor-tight tank, a type of chemical storage tank that allows vapors to collect in the headspace at the top of the tank and exit through a pressure relief vent or sent to a vapor treatment system for remediation. A vapor-tight tank should be used when storing groundwater contaminated with a chemical such as benzene that will emit a hazardous gas, for example. These tanks are also ideal for containing liquids that may emit harmful chemical vapors. This type of frac tank is commonly used in chemical processing plants, industrial plants and oil drilling applications.

Environmental regulation agencies establish rules around the emission of VOC (volatile organic compounds) vapors from frac tanks. A vapor-tight tank includes piping connections that can be used to carries the vapors to a processing area where the vapors can be treated before they are released into the atmosphere. This also eliminates the possibility of heavier vapors, such as gasoline, settling around the exterior of the tank and creating the conditions for a flash vapor fire if an ignition source were to be introduced into the area.

Single wall vs. double wall frac tanks

A single wall frac tank is suitable for most applications. If the frac tank is positioned near a body of water, a wetland or wildlife preserve, however, a double wall frac tank will help ensure that the stored liquid does not leak out. These tanks are essentially constructed as one tank inside of another. If a leak occurs in the inner tank, the outer tank will contain it.

Adding a spill containment berm provides additional protection against any leaks from the outer tank, buying time to clean up the liquid before it may overflow the containment berm and contact the environment.

Specialty frac tanks

Some frac tanks are purpose-built to serve specific needs.

Vertical frac tanks, also called upright frac tanks, have become more popular in the industrial markets over the last few years due to their smaller ground footprint. The vertical tanks typically have a storage capacity of 350 barrels. Often you can place three of these tanks in the same space that a traditional frac tank requires. Customers typically utilize a 50 ton crane to “stand up” these type of tanks once they arrive at the site. Some versions feature a cone bottom for drainage.

Steam-Coil frac tanks, have a steam coil running through the inside of the tank. The coil allows steam to be piped through the tank where the radiant heat of the piping is in direct contact with the stored materials. This process heats the stored liquid and helps keep the contents from cooling and solidifying in cold environments.

Mix tanks, or chemical storage mixing tanks, are popular at refineries, chemical facilities and wastewater treatment plants. They have mixing blades as well as steam heating coils. This type of tank is used to create slurries or to keep solids in suspension to enable futher processing.

Gas buster tanks are commonly used during pipeline pigging (clearing the pipe by pushing a cylindrical “pig,” or plug, through it). They also increase safety when pigging overhead industrial piping. When the liquid exits the pipe, it may contain trapped compressed air that could cause a closed top frac tank to rupture as the compressed air rapidly expands or cause the liquid to gush out of an open top frac tank. Neither scenario will happen with a gas buster tank thanks to large, heavy-walled piping at the top that contains the surge of liquid and compressed air as it directs the flow through downward facing slots in the heavy walled piping located in the top of the tank.

The value of partnering with frac tank experts

Choosing the ideal frac tank for your operation can increase safety, ensure regulatory compliance, drive efficiencies and even reduce manhours on a project. But frac tank selection is complex, and the best storage or filtration solution for your application may be one you’re not even aware of or haven’t considered.

Working with a temporary equipment vendor that offers deep expertise in fluid management and an extensive fleet of frac tanks from multiple frac tank manufacturers will help ensure you get the right tank when and where you need it. United Rentals has a dedicated team of fluid solutions experts who will ask all the essential questions about the liquids being stored and confirm that the tank you choose has the attributes and piping connections to help you safely and efficiently perform your next project.

Contact the United Rentals Fluid Solution Group today for all your frac tank needs.