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.

What are oil storage tanks?

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.

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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.

Functions of tanks in the energy sector

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 653. In addition, an efficient design allows stabilizing operation flows, improving inventory control and reducing evaporation losses.

How are petroleum products stored?

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.

Types of industrial storage tanks

According to operating pressure

Atmospheric: up to 1 psig. Standards: API 650, API 12C, API 653.
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.

1 IMG 1 ING shutterstock 2366281505 Hydrocarbon storage tanks function types and Standards copia — Figure 1. Inspection of the floating roof of a storage tank in a refinery unit.

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.

Regulations applied to hydrocarbon tanks

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.

Key considerations for tank type selection

Tank type selection must consider multiple technical, logistical and regulatory factors. An inappropriate choice can affect operational efficiency and safety, and even compromise the service life of the storage system.

Correctly analyzing the types of storage tanks available is key to adapt the technical solution to the specific needs of the project.

Among the most relevant criteria are

Nature of the product: light and heavy hydrocarbons require tanks with different characteristics.
Climatic conditions: Cold regions may require thermal insulation or heating systems.
Available space: Urban sites or sites with logistical restrictions condition the shape and orientation of the tank.
Local and international API regulations: Current legislation may limit the use of certain designs.

Industrial applications and usage scenarios

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.

Preventive and scheduled maintenance according to API 653

Maintenance is important to avoid structural failures, leaks and accidents. API 653 establishes guidelines for the inspection, repair and reconstruction of welded steel tanks operating at atmospheric pressure.

Types of inspection

External visual: Every 5 years or sooner, check corrosion, paint and deformations.
Internal: Every 10 years or less, evaluates thickness, bottom and internal corrosion in storage tanks.
Non-destructive: Ultrasound, liquid penetrant or X-ray.

In addition to periodic inspections, it is key to understand the failure modes in storage tanks, which are discussed in depth in this complementary inspenet article: “Failure modes in hydrocarbon storage tanks”.

Modern strategies

Nowadays, maintenance strategies incorporate predictive techniques and Risk Based Inspection (RBI) methodologies, pillars of modern digital monitoring in industrial tanks. This approach allows prioritizing interventions considering factors such as service severity, tank age, failure history and specific environmental conditions.

Technical record for traceability

All interventions should be documented with full traceability, including materials, repair methods and qualified personnel. Well-planned maintenance extends service life, reduces operating costs and raises plant safety standards.

Certified inspection personnel

Having personnel certified in standards such as API 653 is a prerequisite to ensure accurate and safe evaluations. These professionals are trained to interpret technical criteria, apply advanced inspection methods and execute maintenance decisions according to international standards.

Interested in storage tank inspection?

Don’t miss this exclusive interview with John Cornell, President of H.I.R. Technical Services and an international benchmark in tank inspection. Discover key insights, best practices and field experiences that only a true expert can share.

Play and learn from the best! Watch full interview on Inspenet TV

Trends in digital tank monitoring

The digital transformation in the energy sector has driven the use of advanced technologies such as smart sensors, SCADA systems, industrial IoT and digital twins to monitor the integrity of storage tanks in real time.

These solutions enable continuous monitoring of critical variables such as internal pressure, temperature, corrosion, fill levels and emissions, facilitating data-driven decision making and improving operational efficiency. Figure 2, shows a conceptual image of digital transformation applied to oil and gas plants through sensors, IoT networks and smart systems.

1 IMG 2 ING shutterstock 515714224Hydrocarbon storage tanks function types and Standards copia 1 — Figure 2. Visualization of the concept of digital transformation in the hydrocarbon industry.

Digital twins make it possible to simulate operational scenarios, plan interventions without interrupting actual service and analyze the structural behavior of the tank under extreme or unforeseen conditions. Dragsa, in its official platform, details how this technology contributes to optimize the management of industrial assets through the digitization of tanks and storage networks.

Currently, these technologies are an essential part of mechanical integrity programs in hydrocarbon storage tanks, ensuring greater traceability, regulatory compliance and environmental control.

The adoption of digital solutions not only strengthens industrial safety, but also represents a tangible competitive advantage for companies seeking to differentiate themselves in efficiency and sustainability within the energy sector.

Conclusion

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.

Apply the right standards and avoid critical failures in your storage system!