Storage tanks are essential components in oil, gas, and petrochemical industries, responsible for holding vast volumes of volatile liquids. These liquids—such as crude oil, gasoline, jet fuel, diesel, and various petrochemicals—must be stored in a manner that ensures safety, minimizes product loss, and remains compliant with stringent environmental regulations. Two predominant tank designs in use today are internal floating roof tanks(IFRTs) and external floating roof tanks (EFRTs). While both aim to reduce vapor emissions and improve safety, they differ significantly in structure, performance, and application.
Understanding the differences between these two designs allows plant engineers, safety officers, and procurement teams to make informed decisions.
What Is an Internal Floating Roof Tank (IFRT)?
An internal floating roof tank (IFRT) is a specialized storage tank designed with a fixed external roof and an additional floating roof inside the tank. This internal floating roof rests directly on the surface of the stored liquid and moves up or down as the liquid level changes. By “riding” the liquid surface, the floating roof significantly reduces the vapor space above the liquid, helping to minimize vapor formation and emissions.
Structural Design
The IFRT combines the benefits of a fixed roof tank with those of a floating roof. The outer fixed roof protects the tank from external elements such as rain, dust, and sunlight, while the internal floating roof provides an effective barrier that “floats” on the liquid. The floating roof is typically constructed from lightweight but durable materials like aluminum or stainless steel and is supported by pontoons or legs that keep it buoyant. Seals around the edges prevent vapors from escaping, ensuring the tank maintains low emissions and improved safety.
Typical Applications
IFRTs are widely used in industries storing highly volatile and flammable liquids, including gasoline, jet fuel, and light petrochemical products. Because these substances are prone to evaporation and pose significant fire hazards, IFRTs help facilities meet strict safety and environmental regulations, such as the U.S. Environmental Protection Agency’s Clean Air Act.
Benefits
Internal floating roof tanks offer superior vapor control by virtually eliminating the vapor space above the liquid, reducing volatile organic compound (VOC) emissions by up to 98%. Their enclosed design provides enhanced fire protection by keeping vapors contained beneath the fixed roof, reducing the risk of ignition. Additionally, the fixed roof prevents contamination from external pollutants such as rainwater, dust, and debris, which can compromise product quality. These tanks also help companies maintain compliance with stringent environmental and safety standards worldwide.
Drawbacks
While IFRTs provide excellent performance, they have a higher initial capital cost due to their more complex design and construction. Maintenance is also more involved, requiring regular inspections of seals, pontoons, roof legs, and drainage systems to ensure optimal performance and safety. Proper upkeep is essential to avoid leaks, corrosion, and mechanical failures over the tank’s lifespan.
What Is an External Floating Roof Tank (EFRT)?
An external floating roof tank (EFRT) is a type of storage tank commonly used in the oil, gas, and petrochemical industries for holding moderately volatile liquids. Unlike fixed roof tanks, EFRTs do not have a permanent, stationary roof. Instead, they feature a floating roof that rests directly on the liquid surface inside the tank. This floating roof moves up and down with the liquid level, helping to reduce vapor space and minimize evaporation losses. Since the floating roof is exposed directly to the outside environment, it is designed to withstand various weather conditions.
Structural Design
The design of an EFRT includes a cylindrical steel shell that contains the liquid, with a large floating deck resting on the liquid surface. This deck is typically supported by pontoons or other buoyant structures, allowing it to float smoothly as liquid levels rise or fall. The roof’s edge is sealed against the tank wall with flexible rim seals to limit vapor emissions. Because the roof is exposed, drainage systems are incorporated to remove rainwater and prevent excess weight on the floating roof, which could compromise its buoyancy and structural integrity.
Typical Applications
EFRTs are widely used to store hydrocarbons such as crude oil, diesel fuel, and naphtha, which have moderate volatility. These tanks are common in refineries, storage terminals, and other facilities where vapor control is necessary but environmental regulations are not as strict as in some other regions. EFRTs offer a practical and cost-effective solution for storing a variety of liquid hydrocarbons in these settings.
Benefits
One of the main advantages of EFRTs is their lower capital cost compared to more complex tank designs like internal floating roof tanks. The simpler structure makes EFRTs less expensive and quicker to build. Additionally, EFRTs are versatile and suitable for storing a broad range of hydrocarbons with different volatility levels, which provides operational flexibility for various industrial applications.
Drawbacks
Despite these benefits, EFRTs face some challenges. Since the floating roof is exposed directly to the atmosphere, it is vulnerable to damage from weather elements such as rain, wind, and ultraviolet (UV) radiation. This exposure can accelerate wear on seals and structural components, increasing maintenance needs. Moreover, the open design allows vapors to mix with outside air, heightening the risk of fire and explosion hazards. EFRTs are also less effective at controlling vapor loss compared to internal floating roof tanks, which means higher emissions of volatile organic compounds (VOCs). Due to these limitations, EFRTs may not comply with strict environmental regulations in sensitive or highly regulated regions.
Key Differences Between IFRTs and EFRTs
The key differences between Internal Floating Roof Tanks (IFRTs) and External Floating Roof Tanks (EFRTs) largely revolve around their design, performance, and suitability for different storage needs. IFRTs feature a floating roof located beneath a fixed outer roof inside the tank, which effectively eliminates vapor space and provides excellent vapor control. This design can reduce volatile organic compound (VOC) emissions by up to 98%, making IFRTs highly effective for storing highly volatile liquids such as gasoline and jet fuel. Because the floating roof is enclosed, the risk of fire and explosion is significantly lower, as vapors are contained and protected from ignition sources.
In contrast, EFRTs have a floating roof that is exposed directly to the atmosphere. While they reduce vapor loss compared to fixed roof tanks, their vapor control is less effective than IFRTs, resulting in moderate VOC emissions. EFRTs are typically used for liquids with medium volatility, such as crude oil and diesel fuel. Due to their exposed design, EFRTs face higher risks of fire and explosion and can suffer damage from weather conditions like high winds or heavy snow loads.
Construction costs for IFRTs tend to be higher due to their more complex design, while EFRTs are generally simpler and less expensive to build. Maintenance requirements for IFRTs involve routine inspections of seals and pontoons, but the enclosed nature of the tank protects these components from weather-related wear. On the other hand, EFRTs require regular seal inspections and face greater risks of weather damage, which can increase maintenance efforts. Overall, IFRTs offer lower environmental impact and superior climate resilience, making them the preferred choice when strict emissions control and safety are priorities.
Importance of Regular Inspection and Maintenance
No matter which type of floating roof tank is chosen, regular inspection, maintenance, and repair are essential:
Key Inspection Areas
Roof Deck: Look for corrosion, dents, or deformation.
Pontoons: Check buoyancy and structural integrity.
Seals: Inspect for wear, cracking, or detachment.
Drainage Systems: Ensure water drains properly to prevent leakage.
Foundation: Watch for subsidence or settlement signs.
Maintenance Actions
Seal Replacement: Every few years or as needed.
Roof Leg Adjustment: Ensure even support.
Cleaning: Remove debris, especially after storms.
Static Grounding Repair: Maintain grounding to prevent sparks.
Neglect can lead to safety risks, VOC emissions, product loss, and structural degradation.
Conclusion
Choosing between a fixed roof, an Internal Floating Roof Tank (IFRT), or an External Floating Roof Tank (EFRT) depends on your operational needs, safety goals, and regulatory obligations. IFRTs provide superior vapor control, environmental protection, and fire safety—making them ideal for volatile liquids and compliance-driven industries. While EFRTs offer cost-efficiency and flexibility, they lack the containment performance of IFR systems.
To ensure maximum safety, compliance, and storage efficiency, many industry leaders are turning to high-performance internal floating roof solutions. Lianyungang Bona Bangwei Petrochemical Equipment Co., Ltd. specializes in designing and manufacturing advanced IFR systems tailored to diverse storage needs. Whether you are planning a new project or upgrading existing tanks, contact them today to explore customized solutions that meet international safety and emission standards.
