STI F921® tanks are a specialized subtype of UL-142 aboveground steel storage tanks designed with double-wall construction and a built-in interstitial space for leak monitoring. Developed by the Steel Tank Institute (STI), the F921® specification provides an added layer of environmental protection by combining primary storage and secondary containment within a single tank system.
These tanks are commonly selected for industrial, commercial, municipal, and institutional applications where spill prevention, leak detection, and regulatory compliance are important considerations. Steel Tank and Fabricating Corp. manufactures STI F921® tanks in a variety of configurations to meet the unique requirements of each facility.
What Is an F921® Tank?
An STI F921® tank is a factory-fabricated steel storage tank featuring both an inner storage tank and an outer containment wall. The space between these two walls, known as the interstice, can be monitored to help identify leaks before they become costly environmental incidents.
By incorporating secondary containment directly into the tank design, F921® tanks provide an efficient alternative to traditional containment methods that rely on external dikes, berms, or concrete structures. The result is a compact storage solution that offers both product storage and environmental protection within a single system.
F921® tanks are manufactured in accordance with UL-142 construction requirements and may be supplied with the STI F921® listing label when applicable.
Key Features
STI F921® tanks combine the benefits of UL-142 aboveground storage with integrated secondary containment and leak monitoring capabilities. Key features include:
- Double-wall steel construction with a monitored interstitial space
- Vertical tank designs available with leg or skirt supports
- Integral support options including saddles and skids
- Engineering support available for seismic and site-specific requirements
Benefits of F921® Double-Wall Construction
The primary advantage of an F921® tank is its integrated secondary containment system. Because containment is built directly into the tank, facilities gain an additional level of environmental protection while simplifying site design and reducing the need for separate containment infrastructure.
The monitored interstitial space also provides operators with a convenient way to verify tank integrity. Early leak detection can help reduce product loss, minimize cleanup costs, and support compliance with environmental regulations.
In addition, the aboveground design allows for straightforward visual inspections and easier access for maintenance personnel. For many facilities, an F921® tank offers the benefits of both aboveground storage and secondary containment in a single package.
Applications
F921® tanks are commonly used wherever facilities require an added level of containment assurance and leak detection capability. Typical applications include:
- Petroleum and diesel fuel storage
- Generator and backup power systems
- Industrial process liquids
- Manufacturing, municipal, utility, and institutional facilities
These tanks are particularly well suited for sites requiring additional containment assurance, installations where aboveground leak monitoring is preferred, and facilities looking to avoid separate dike or berm systems.
Available Configurations
Steel Tank and Fabricating Corp. can manufacture F921® tanks with a variety of options to meet project requirements, including:
- Leg-supported or skirt-supported vertical tanks
- Saddle-mounted and skid-mounted designs
- Custom nozzle and connection layouts
- Monitoring systems, access platforms, and specialty coatings
Our engineering team can also provide support designs for site-specific seismic requirements and other specialized conditions.
Why Choose an STI F921® Tank?
For many facility owners and operators, STI F921® tanks provide an attractive balance of environmental protection, operational efficiency, and installation flexibility. By integrating secondary containment directly into the tank design, F921® tanks help simplify projects while providing a reliable solution for aboveground liquid storage.
Whether you’re storing fuel, process liquids, or other regulated products, an F921® tank can help support compliance objectives while reducing the complexity associated with traditional containment methods.
Quality Manufacturing and Engineering Support
Every STI F921® tank is manufactured using proven steel fabrication practices and undergoes quality control procedures throughout the production process. Our team works closely with customers, engineers, and contractors to ensure each tank is designed and manufactured to meet operational, regulatory, and project-specific requirements.
Whether you need a standard configuration or a custom-engineered solution, Steel Tank and Fabricating Corp. has the experience and manufacturing capabilities to deliver a reliable storage tank system built for long-term performance.
Request a Quote
If you’re evaluating aboveground storage options that require integrated secondary containment and leak monitoring, contact STAFCO to discuss your application. Our team can help you determine whether an STI F921® tank is the right solution for your project and provide a customized quotation.
