Floating roof tanks—whether internal or external—play a vital role in storing large volumes of flammable or volatile liquids in industries such as petroleum, petrochemicals, and chemical manufacturing. These tanks are designed to minimize vapor loss, improve safety, and comply with environmental regulations by using a roof that rises and falls with the liquid level.
Within an internal floating rooftank(IFRT) configuration, an additional floating roof operates under a fixed outer roof—keeping vapors contained and protected from external elements. Though several components contribute to an IFRT’s functionality, one part stands out as the most crucial: the seal system. A high-performing seal system directly affects vapor control, operational safety, emission levels, and long-term reliability.
Key Components of a Floating Roof Tank
A floating roof tank is designed to safely store volatile liquids such as crude oil, gasoline, and chemicals. Its unique structure includes several critical components that work in tandem to ensure safe, efficient, and environmentally compliant storage. These components minimize vapor losses, protect the stored product, and reduce fire risks. Below are the key elements of a floating roof tank, with an emphasis on internal floating roof (IFR) systems:
Floating Roof Deck
Types: Pan-type, pontoon-type, or double-deck structures
Function: The floating roof deck rests directly on the liquid surface inside the tank. Its primary role is to reduce the vapor space above the liquid, which significantly cuts down on evaporative losses.
Placement in IFRs: In internal floating rooftanks, this deck is positioned beneath a fixed outer roof. This configuration protects the floating roof from external weather conditions such as rain, wind, and sunlight, thereby extending its lifespan and maintaining structural integrity.
Note: The type of deck used depends on factors like tank diameter, stored liquid type, and operating conditions.
Sealing System
Components: Primary and secondary seals installed around the perimeter of the floating roof deck
Function: The seal system closes the gap between the tank shell and the edge of the floating roof, preventing vapors from escaping into the atmosphere.
Significance: This system is arguably the most crucial component for controlling emissions, maintaining air quality, and ensuring workplace safety. A well-maintained sealing system ensures compliance with environmental regulations such as the U.S. EPA’s NSPS (New Source Performance Standards) and similar global standards.
Highlight: Leaking or damaged seals can result in significant product losses, increased emissions, and even catastrophic accidents due to flammable vapor accumulation.
Support Legs and Guidance System
Purpose: Support legs allow the floating roof to rest safely above the tank floor when liquid levels are low.
Guidance System: Vertical guide poles or columns keep the floating roof properly aligned as it rises and falls with the product level.
Importance: Misalignment or unstable support can compromise seal integrity and increase the risk of emissions or mechanical failure.
Drainage System
Used to: Drain rainwater and prevent accumulation on the roof deck, which can lead to excessive loading and structural damage.
In IFRs: Though the internal roof is shielded from external weather, condensation or minor leaks from the fixed roof can still occur. Internal drain lines are installed to safely remove any collected water and maintain tank integrity.
Roof Vents and Anti-Static Features
Vents: These are critical for equalizing pressure within the tank as the floating roof moves up or down. Without proper venting, pressure differences can lead to roof deformation or seal damage.
Grounding Mesh and Anti-Static Measures: These prevent the build-up of static electricity, which could otherwise ignite flammable vapors. All floating roofs must be properly grounded or equipped with anti-static cables to maintain safe operation.
The Sealing System: The Most Critical Component
Why Seals Are Essential for Vapor Control
The seal system is the primary defense against vapor escape. Even with a floating roof, tiny gaps between the roof edge and the tank wall can allow vapors—especially volatile organic compounds (VOCs)—to escape. Seals bridge this gap, maintaining near-zero vapor space and preventing harmful emissions.
Primary Seals
These flexible rubber or composite strips create a tight contact with the tank wall. They adapt to the roof’s vertical movement, minimizing vapor leakage and ensuring a consistent seal.
Secondary Seals
Installed above or immediately adjacent to primary seals, secondary seals add a redundant layer of protection. In IFRs, where external elements are already blocked, secondary seals mainly guard against weather impacts and minor roof misalignment.
Impact of Poor Seal Performance
Increased VOC emissions due to vapor leaks
Safety hazards, as vapor buildup could create explosive conditions
Regulatory non-compliance, leading to fines or operational shutdowns
Product loss, decreasing profitability and efficiency
Given these stakes, the sealing system’s integrity is absolutely vital.
Types of Seals and Their Materials
Seal Designs
Mechanical Shoe Seals Metal-backed seals that slide up and down the tank wall, ideal for tanks with significant roof movement.
Liquid-Mounted Seals Use the stored liquid to press the seal against the shell. They are simpler and less costly but wear faster.
Vapor-Mounted Seals Use tight tolerance to trap vapor and prevent leakage. They rely on foam filler or spring tension.
Environmental Impact: VOCs contribute to smog and climate change Failing seals can cause serious financial, environmental, and safety consequences.
Seal Inspection and Maintenance Best Practices
Inspection Schedules
Monthly Visual Checks: Look for wear, joint gaps, or seal displacement
Annual Detailed Review: Measure gap tolerances, inspect materials
Compliance Inspections: Follow API 1634, EPA Subpart WW, or local standards
Techniques and Measurements
Check for seal compression consistency
Gap measurement between seal and shell
Inspect support leg alignment for smooth roof movement
Review drain and vent integrity
Maintenance Actions
Tighten or replace seals when wear is detected
Adjust roof-leg guides to prevent seal wear
Clean decks and drains to minimize debris damage
Repair or apply coatings to prolong seal life
Regular maintenance ensures that seal systems perform effectively over the tank’s lifespan.
Conclusion
In an internal floating roof tank, the sealing system is the most critical component. It minimizes vapor emissions, prevents hazardous vapor buildup, and protects both product quality and environmental compliance. Faulty or worn seals can lead to safety hazards, regulatory penalties, and significant revenue loss. On the other hand, investing in high-quality seals and regular maintenance ensures safer operations, reduced emissions, and longer tank life.
To safeguard your storage system, choosing a trusted partner for sealing solutions is essential. Hoto Heating Equipment Co., Ltd. offers advanced, reliable sealing systems tailored for internal floating roof tanks. For more information or expert guidance, we recommend reaching out to Hoto today.
Lianyungang Bona bangwei Petrochemical Equipment Co., Ltd. it’s located in the bridgehead of Eurasia, Jiangsu Lianyungang, with the broad mind of the Yellow Sea, creating the magical wisdom of Huaguo Mountain.
