Static Equipment in Oil and Gas Industry – Storage Tanks, Types, Working & Interview Questions

In the oil and gas industry, handling fluids safely and efficiently is critical. This is achieved using different types of equipment, broadly classified into static equipment and rotating equipment.

Among these, static equipment forms the backbone of process plants. These components operate without movement and are essential for storage, separation, and heat transfer operations.

What is Static Equipment?

Static equipment refers to mechanical components that do not have any moving or rotating parts during operation. These equipment remain stationary and perform important process functions.

Main functions include:

• Storage of fluids
• Heat transfer
• Separation of phases
• Pressure containment

Examples of Static Equipment:

• Storage Tanks
• Pressure Vessels
• Heat Exchangers
• Separators
• Filters and Strainers
• Heaters and Boilers

Even small components like vents and strainers play a crucial role in maintaining system efficiency.

Storage Tanks

Storage tanks are one of the most important types of static equipment used in oil and gas facilities. They are used to store liquids and gases such as crude oil, petroleum products, and petrochemicals.

Design of storage tanks depends on:

• Volatility of fluid
• Operating pressure
• Temperature conditions
• Corrosion characteristics

Proper design ensures safety, efficiency, and environmental protection.

Types of Storage Tanks

1. Fixed Roof Tanks

Fixed roof tanks are used for storing low volatile liquids such as diesel and certain petrochemicals. These tanks consist of a cylindrical shell with a permanently fixed roof.

Roof types include:

• Conical roof
• Dome-shaped roof

Modern tanks are fully welded for better leak-proof performance, whereas older tanks were riveted or bolted.

Breather Valve Working

Due to temperature variations, pressure inside the tank changes. A breather valve is installed to maintain safe pressure levels.

• During hot conditions → pressure increases → valve releases vapor
• During cold conditions → pressure decreases → valve allows air inside

This prevents tank failure due to overpressure or vacuum conditions.

2. Floating Roof Tanks

Floating roof tanks are designed for highly volatile liquids such as gasoline and crude oil.

In fixed roof tanks, vapor space above liquid causes evaporation losses and fire hazards. Floating roof tanks eliminate this space by resting directly on the liquid surface.

Advantages:

• Reduces evaporation losses
• Minimizes fire hazards
• Controls vapor emissions

Types of Floating Roof Tanks

• External Floating Roof (EFR): Roof exposed to atmosphere
• Internal Floating Roof (IFR): Floating roof inside fixed tank
• Dome Roof Tank: Floating roof with additional dome protection

Tank Classification Based on Orientation

Horizontal Tanks

Used for small storage capacity and gaseous products. These tanks are easy to install and transport.

Vertical Tanks

Used for large-scale storage of liquids. Commonly found in refineries and storage terminals.

Spherical Tanks

Spherical tanks are used for storing high-pressure gases such as LPG.

Advantages:

• Uniform stress distribution
• High strength for pressure storage
• Reduced surface area

Dykes (Bund Walls)

Dykes are protective walls constructed around storage tanks to contain leaks or spills and prevent accidents.

They are especially important in tank farms where multiple tanks are installed close to each other.

Importance of Storage Tanks in Piping Systems

• Provide storage and buffering
• Maintain steady flow conditions
• Ensure safety during operations
• Support continuous plant operation

Advantages of Static Equipment

• Simple design
• Low maintenance
• High reliability
• Long service life

Limitations of Static Equipment

• No energy generation capability
• Passive operation
• Requires proper design for pressure and temperature

Conclusion

Static equipment plays a fundamental role in oil and gas operations. Storage tanks are essential for safe storage, process stability, and continuous operation.

Understanding tank types and working principles is very important for every piping engineer.

Interview Questions and Answers – Static Equipment (Detailed)

1. What is static equipment?

Static equipment refers to mechanical equipment that does not have moving or rotating parts. It is mainly used for storage, heat transfer, and separation processes in industries like oil and gas.

2. Give examples of static equipment.

Examples include storage tanks, pressure vessels, heat exchangers, separators, filters, and boilers.

3. What is a storage tank?

A storage tank is a container used to store liquids or gases safely under specific temperature and pressure conditions in industrial facilities.

4. What are the main types of storage tanks?

• Fixed roof tanks
• Floating roof tanks
• Spherical tanks

5. What is a fixed roof tank?

A fixed roof tank has a permanently attached roof and is used for storing low volatile liquids where vapor loss is minimal.

6. What is a floating roof tank?

A floating roof tank has a roof that floats directly on the liquid surface, reducing vapor space and minimizing evaporation losses.

7. What is a breather valve?

A breather valve is a safety device that maintains pressure inside a tank by allowing air to enter or exit based on internal pressure changes.

8. Why are spherical tanks used?

Spherical tanks are used for storing high-pressure gases because they provide uniform stress distribution and high structural strength.

9. What is a dyke or bund wall?

A dyke is a protective wall constructed around tanks to contain leakage and prevent the spread of hazardous fluids.

10. Why is static equipment important?

Static equipment is important because it ensures safe storage, process stability, and continuous operation in industrial plants.

11. What factors affect tank selection?

• Type of fluid
• Pressure conditions
• Temperature
• Volatility
• Corrosion properties

12. What is the role of tanks in piping systems?

Tanks provide storage, help maintain steady flow, and act as buffers in piping systems.

13. What is volatility?

Volatility is the tendency of a liquid to evaporate. High volatility means higher vapor formation.

14. Why do floating roof tanks reduce losses?

Floating roofs eliminate the vapor space above the liquid, reducing evaporation losses and emissions.

15. Difference between horizontal and vertical tanks?

Horizontal tanks are used for small capacity storage and gases, while vertical tanks are used for large-scale liquid storage.

Final Interview Tip

During interviews, always explain answers with practical examples. This shows real understanding and increases your chances of selection.