Crude Oil Storage Tanks and Their Applications

Storing crude oil is a crucial part of the oil production process. The development of an oil field typically involves many production wells connected to fluid transportation systems that refine crude oil according to sales specifications before export or sale to refineries.

Storage tanks serve as an initial area for staging crude oil and, in some cases, for final refinement before transportation. Often, continuous export of crude oil during production is not feasible; thus, it is essential to store it for a certain period.

Generally, crude oil storage tanks refer to large storage facilities used for the temporary storage of crude oil in a controlled environment, allowing the oil to be transformed into other petroleum products at various stages.

These tanks are constructed from materials such as stainless steel, polyethylene, composites, fiberglass, or double-walled composite materials. Key features of oil tanks include pressure and temperature resistance, prevention of crude oil leakage, and maintaining the quality of petroleum materials. Major applications of these storage tanks include:

Storage and protection of crude oil

Transportation and short-distance transfer of crude oil

Standardizing crude oil quality

Safe and secure storage of crude oil

Preventing environmental pollution

Storing crude oil for loading and distribution

Types of Crude Oil Storage Tanks

Crude oil storage tanks are divided into four different categories, which will be explained below:

Fixed Roof Tanks

External Floating Roof Tanks

Internal Floating Roof Tanks

Horizontal Tanks

Fixed Roof Tank

One type of crude oil storage tank is the fixed roof tank. As the name suggests, it has a fixed roof shaped like a dome or cone, with cylindrical walls. The pressure in this tank is close to atmospheric pressure, and it has a high capacity. One of the features of this type of tank is a vapor vent or breathing valve, which prevents pressure increases during charging and protects the tank from damage.

External Floating Roof Tank

In an external floating roof tank, the roof sits on the crude oil surface during rain and snow but is otherwise exposed to the open air. A drainage path is provided on the floating roof to prevent rainwater and melting snow from entering the tank, directing it to the ground through pipes.

Internal Floating Roof Tank

Where external floating roofs cannot be used, internal floating roofs are employed on crude oil tanks. In this case, the internal floating roof sits on the crude oil surface, while a fixed roof is placed above it. This design prevents additional loads on the floating roof and keeps environmental contaminants from entering the tank.

Horizontal Tank

Another type of crude oil storage tank is the horizontal tank, which is made from stainless steel and reinforced composite polyester or fiberglass. Horizontal tanks are five times longer than their diameter. This five-to-one length-to-diameter ratio maintains structural stability. This type of tank is equipped with pressure vacuum valves.

Safety Considerations for Crude Oil Storage Tanks

Safety measures are one of the most critical aspects of managing crude oil storage tanks, given their flammable nature. Following these guidelines can prevent unforeseen incidents such as fires and environmental damage. Key safety considerations for various types of crude oil storage tanks include:

Fire Prevention Measures: Necessary actions to protect tanks against fire include preparing fire extinguishers, using automatic fire suppression systems, and implementing smoke detection systems. Furthermore, refinery staff should participate in training sessions to learn safe handling of tanks, timely leak detection, and emergency response actions during fire incidents. Training helps staff effectively strengthen safety protocols and respond more quickly to potential fire hazards.

Regular Maintenance and Inspection: Another safety consideration is conducting regular maintenance and inspections of tanks to ensure their integrity. Ensuring the tanks are in good condition helps prevent leaks and spills. Inspections should be conducted at specified intervals.

Leak Detection and Monitoring Systems: To enhance the safety of crude oil storage tanks, monitoring and leak detection systems are employed. These systems vary in type, including measuring systems for automated oil level measurement, leak detection systems for rapid leak identification, and dikes or containment basins for secondary containment of oil spills.

Selection Criteria for Refinery Tanks

Choosing refinery tanks requires attention to various important aspects to optimize both technical and safety considerations. Considering these factors helps improve performance, increase safety, and reduce maintenance and operational costs for refinery tanks. The following are key considerations:

Type of Tank:

Fixed Roof Tanks: For storing crude oil and petroleum products with low vapor pressure.

Floating Roof Tanks: For materials with high vapor pressure that require evaporation reduction.

Pressure Tanks: For storing liquefied gases or high-pressure products.

Tank Capacity:

Depending on the production volume and storage needs of the refinery, an appropriate capacity must be selected.

Larger tanks require more space and have higher construction and maintenance costs.

Tank Construction Materials:

Carbon Steel: Suitable for most petroleum products.

Stainless Steel: For corrosive materials.

Special Alloys: For materials with specific chemical properties.

Tank Installation Location:

Assessing geological conditions of the installation site.

Avoiding seismic zones.

Access to transportation routes and refinery facilities.

Safety and Protective Systems:

Installing fire alarm and suppression systems.

Having adequate ventilation systems to prevent accumulation of hazardous vapors.

Designing to prevent leaks and environmental contamination.

Standards and Regulations:

Adhering to international and national standards for design, construction, and maintenance of tanks.

Considering environmental and occupational safety regulations.

Costs:

Construction and installation costs of the tank.

Periodic maintenance and repair costs.

Costs related to safety and protective systems.

Environmental Factors:

Resistance to regional weather conditions (temperature, humidity, wind, etc.).

Environmental impacts like corrosion and rusting.

Technology and Equipment:

Utilizing advanced technologies for monitoring and controlling conditions inside the tank.

Systems for measuring level and temperature.

Maintenance and Repairs:

Designing for easy access for periodic maintenance and inspections.

Planning for alternative systems during maintenance periods.

Testing Related to Crude Oil Storage Tanks

The most important tests for assessing the integrity of crude oil tanks include:

Magnetic Flux Leakage Testing (MFL): Using strong magnets to inspect tank floor plates for corrosion and deterioration.

Ultrasonic Testing (UT): Utilizing crawlers to assess the condition of the tank shell or roof from a distance without ropes or scaffolding.

Phased Array Ultrasonic Testing (PAUT): For mapping corrosion and accurately detecting defects in tanks.

Remote Visual Inspection (RVI): Using robotic crawlers for visual inspections.

Alternating Current Field Measurement (ACFM): For inspecting and precisely detecting internal and external weld cracks in crude oil storage tanks.

Pulsed Eddy Current (PEC) Testing: For inspecting the annular section of crude oil storage tanks.

Pipescan or MFL Inspection: For quick and precise examination of piping associated with tanks.

Sealing Oil Tanks with Geomembranes

Geomembrane sheets are one type of geosynthetic product with a uniform, impermeable surface, widely used across various industries and made from polymer materials like polyethylene.

One of the most significant applications of this product is sealing crude oil storage tanks. The main objective of sealing tanks with geomembranes is to prevent the degradation of crude oil quality. The sealing prevents water and other substances from entering the tank.

Key advantages of using geomembranes for sealing include preventing water and air infiltration, stopping the release of hazardous materials into the environment, and increasing the tank's resistance to microorganisms due to high chemical resistance.

For this type of sealing, several considerations are necessary. Firstly, before isolating the geomembrane sheets, a small-scale sample model should be prepared to ensure the sheet quality and the functionality of the welding equipment used. Edge welding of the tank’s seams requires meticulous attention. The pipes used in crude oil storage tanks should be made of polyethylene to connect to the geomembrane.

Conclusion

In this article from Farnam Besspar, we first discussed crude oil storage tanks and their applications, explaining that these large tanks are used for the temporary storage and preservation of crude oil since immediate export right after production is often not possible, and the product must be stored in tanks until then.

We introduced the types of crude oil storage tanks, including fixed roof tanks, external floating roof tanks, internal floating roof tanks, and horizontal tanks, along with the characteristics of each.

Safety considerations regarding crude oil storage tanks included fire prevention measures, regular maintenance and inspections, and the use of monitoring and leak detection systems. We also discussed tests related to crude oil tanks and the sealing of oil tanks with geomembranes. We hope the information provided in this article has been sufficiently comprehensive.

Crude Oil Storage Tanks: Understanding Types, Applications, and Selection Criteria

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