Oil storage tanks: function, types and standards

In the refining industry, oil storage tanks are indispensable for containing large volumes of flammable liquids within the oil supply chain. These units enable safe operation in production, transportation, distribution, and storage of strategic hydrocarbons.

Their design, operation, and maintenance are regulated by API standards, ensuring structural integrity, operational safety and environmental compliance. This article describes the main functions, the most commonly used types of storage tanks and the current API tank regulations, aimed at professionals and organizations in the energy and industrial sector.

Hydrocarbon storage tanks are industrial containers designed to safely store products such as crude oil, gasoline, or diesel fuel. They are cylindrical and vertical, with fixed or floating roofs, and operate at atmospheric pressure.

They are used throughout the energy chain to maintain strategic inventories, support the operation of refineries and ensure the continuous supply of the domestic market, and play an important logistical role in port terminals, chemical plants and national distribution networks.

Depending on their location, they fulfill the following functions:

• Receiving: They store crude oil from wells or processing plants.
• Intermediate: Act as buffers between processes.
• Dispatch: Allow transfer to pipelines, ships, or tankers.
• Mixing: Some tanks agitate the content to homogenize it.
• Separation: They help decant water and sediments from hydrocarbons.

Each function conditions the tank design and must comply with the requirements of standards such as API 650. In addition, an efficient design allows stabilizing operation flows, improving inventory control and reducing evaporation losses.

Hydrocarbon storage is critical in energy logistics. In oil fields, small, modular tanks are used, while in refineries and terminals, large-volume tanks welded on-site predominate.

In addition, in urban distribution centers, compact, buried or vertical tanks are used, adapted to reduced spaces and with automated measurement and safety systems.

Particularities of crude oil

• High viscosity: Requires insulation or heating systems.
• Presence of sediments: Requires decanting prior to refining.
• Corrosive compounds (hydrogen sulfide (H₂S), carbon dioxide (CO₂), naphthenic acids and chlorides : Demands materials with special coatings.

These factors determine robust designs that ensure durability, safety and compliance with increasingly demanding tank regulations.

According to operating pressure

• Atmospheric: up to 1 psig. Standards: API 650, API 12C.
• Low pressure: up to 1.055 kg/cm². Standard: API 620.
• High pressure: for volatile fluids. Standards: API 620, ASME.
• Refrigerated: for cryogenic gases. Standards: API 625, ASME.

According to structural shape

• Vertical cylindrical: most commonly used in refineries.
• Spherical: preferred for gases such as LPG.
• Horizontal/mobile: in temporary or field installations.

Depending on roof design

• Fixed roof: for stable products.
• Floating roof: minimizes evaporation losses (Figure 1).
• Geodesic dome: light, resistant, improves atmospheric sealing.

Types of tanks according to their mobility

• Stationary: fixed in terminals or logistics centers.
• Mobile: Vessels, tankers, tanker trucks or tanker trucks.
• Choosing the right type also depends on the cost of installation, ease of maintenance and desired level of automation. A poorly selected design can result in operational cost overruns and unnecessary risks in the life cycle of the equipment.

Regulatory compliance is fundamental in the design and operation of storage tanks. The most important API tank standards are:

1. API 650: Welded steel atmospheric tanks: Establishes criteria for thicknesses, welds, tests and drains. It is widely applied in refineries and distribution terminals. This standard also considers wind, seismic and hydrostatic pressure loads, ensuring long-term structural integrity.

2. API 620: Low Pressure Tanks: Covers designs for tanks with internal pressures up to 15 psig. It is also used in cryogenic conditions with nickel steel. Its application is frequent in LNG terminals and gas separation processes.

3. API 653: Inspection and maintenance: Key standard for tanks in service. Regulates repairs, inspections, and reconstruction, ensuring its structural integrity. It also applies when the operating conditions are modified or the service life of an existing tank is extended.

4. Other important standards: API 12: for prefabricated modular tanks, NFPA 30: on fire prevention, ASME Section VIII: pressure vessels, ISO 28300 / API 2000: pressure control and venting.

These standards provide a fundamental technical framework to avoid operational incidents and comply with international standards. Their compliance is monitored by regulatory bodies and external audits.

Hydrocarbon storage tanks are used in various industries and logistics environments.

• In refineries, to store crude oil and refined products.
• In export terminals, for dispatch by tankers.
• In chemical and petrochemical plants, as part of the production process.
• In service stations, with underground tanks and control systems.
• At airports, for aviation fuels.

Each operational context requires a particular technical analysis to define the type of tank, the materials and the appropriate instrumentation. It is also important to foresee future expansions, technological upgrades and adaptability to changes in local or international API tank regulations.

A comprehensive design strategy must consider operational safety, energy efficiency, optimized maintenance and proper environmental management, including the impact of managing waste in storage tanks and its proper disposal. These elements are the essential pillars for a sustainable operation in compliance with current regulations.

Hydrocarbon storage tanks are structural components of the energy system. Their selection, design, maintenance and digitalization, aligned with standards such as API 650, API 620 and API 653, optimize the technical management of storage, ensure operational continuity, comply with current regulations and reduce risks to infrastructure, environment and organizational integrity.

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