What Is an Aboveground Storage Tank? Essential Infrastructure for Industrial Liquid Containment
Created on 08.07
What Is an Aboveground Storage Tank? Essential Infrastructure for Industrial Liquid Containment
Across industrial processing plants, petroleum refineries, municipal water utilities, and agricultural facilities, the secure containment of high-volume liquids is an operational necessity. Unlike underground systems hidden from view, aboveground storage tanks (ASTs) are positioned entirely or primarily on the surface of the ground.
Engineered to store everything from crude oil and refined fuels to chemicals, potable water, and industrial wastewater, ASTs offer distinct visibility, easier inspection access, and simpler maintenance protocols compared to below-ground alternatives.
1. Core Design Types and Configurations
Aboveground storage tanks are manufactured in various structural configurations dictated by the volatility, pressure, and chemical properties of the stored product:
● Fixed-Roof Tanks (Cone or Dome Roofs): Featuring a permanently attached roof welded directly to the shell, these tanks are widely used for low-vapour-pressure products such as diesel, fuel oil, water, and heavier chemicals. They require normal and emergency venting to manage internal vapor fluctuations.
● Internal Floating Roof (IFR) Tanks: These combine a fixed outer roof with an internal deck that floats directly on the surface of the liquid. By eliminating the vapor space inside the tank, IFR systems drastically reduce evaporation losses and emissions of volatile organic compounds (VOCs).
● External Floating Roof (EFR) Tanks: Designed without a fixed roof, the open-top vessel features a deck that rises and falls directly with the liquid level. Equipped with specialized rim seals, EFR tanks are standard for large-scale crude oil storage and high-volatility hydrocarbons.
2. Industry Standards and Regulatory Governance
Because ASTs frequently hold flammable, hazardous, or environmentally sensitive materials, their design, fabrication, and operation are strictly governed by internationally recognized engineering standards:
● API 650 (Welded Tanks for Oil Storage): The definitive international standard governing the minimum requirements for material selection, design, fabrication, erection, and inspection of vertical, cylindrical, aboveground welded steel tanks operating at atmospheric or near-atmospheric pressures.
● API 620 and API 653: API 620 governs large, low-pressure storage tanks, while API 653 provides vital protocols for the in-service inspection, repair, alteration, and reconstruction of existing ASTs.
● Environmental and Secondary Containment: Regulatory bodies enforce strict secondary containment mandates (such as concrete dykes, double-walled shells, or impermeable liners) around ASTs to ensure total capture in the event of an accidental spill or tank rupture.
Comparative Matrix: Aboveground vs. Underground Storage Tanks
Evaluation Parameter | Aboveground Storage Tanks (ASTs) | Underground Storage Tanks (USTs) |
Inspection & Monitoring | High visibility; easy routine visual checks for leaks and corrosion | Hidden from view; requires specialized, costly non-destructive testing (NDT) |
Installation Complexity | Faster erection; requires graded foundation pads (ringwalls or crushed stone) | Complex excavation, anchoring to prevent buoyancy, and backfilling |
Environmental Risk Management | Visible leaks are detected immediately; easily paired with secondary dykes | Sub-surface leaks can go unnoticed for long periods, causing severe soil/groundwater contamination |
Space Utilization | Requires dedicated surface footprint space | Frees up surface land for other operational uses |
Frequently Asked Questions (FAQ)
Q: What is an aboveground storage tank (AST)?
A: An aboveground storage tank is a vessel or container positioned entirely or primarily on the surface of the ground, engineered to hold liquids such as petroleum products, chemicals, water, or wastewater.
Q: What primary engineering code governs the design of steel ASTs?
A: The American Petroleum Institute (API) Standard 650 is the international benchmark governing the design, material selection, fabrication, and testing of welded aboveground steel storage tanks.
Q: How are environmental leaks prevented or managed around ASTs?
A: Facilities use secondary containment systems—such as concrete berms, retaining walls, or double-walled tank designs—alongside cathodic protection, specialized coatings, and regular visual inspections to prevent and contain potential spills.
Q: Why are floating roofs used on certain aboveground storage tanks?
A: Internal or external floating roofs rest directly on the liquid surface, eliminating vapor pockets. This minimizes product evaporation losses, reduces harmful emissions, and decreases fire hazards when storing volatile liquids like gasoline and crude oil.
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