 |
| Crude Oil Storage Tank |
Crude Oil Storage Tank
Crude oil storage tanks are vital for the oil and gas industry, requiring careful consideration of design, materials, location, and safety features to prevent accidents and environmental damage. These tanks must be built to withstand tough conditions and maintain the quality of the crude oil, often adhering to industry standards like API 650 and API 620. In India, the Directorate General of Mines Safety (DGMS) sets the safety regulations for oil mines, including those concerning storage tanks, dykes, and valves, primarily through the Oil Mines Regulations, 1984. These regulations cover everything from tank construction and the required capacity of secondary containment (dykes) to the specifications and maintenance of valves, including emergency shut-off valves.
The Oil Mines Regulations, 1984, mandate regular inspections and maintenance of tanks, dykes, and valves to ensure they function correctly. Dykes must be able to contain at least 110% of the largest tank's capacity within the enclosure to handle potential spills. The regulations also emphasize the importance of proper drainage systems to prevent flammable liquid buildup within dykes and the availability of firefighting equipment. For more detailed information, it's recommended to consult the full text of the Oil Mines Regulations, 1984, on the DGMS website. Furthermore, guidelines from the Oil Industry Safety Directorate (OISD), such as OISD Standard 118, provide additional recommendations for oil and gas installations, including storage tanks and related safety measures. Following these regulations and standards is crucial for ensuring the safety of workers, the environment, and the facilities themselves.
Definition
A crude oil storage tank is a large container used for the temporary storage of crude oil before it is transported for refining or distribution. These tanks are designed to hold large quantities of oil safely, preventing leaks, evaporation, and environmental hazards.Location of Crude Oil Storage Tanks
Crude oil storage tanks are strategically located based on the supply chain needs. The primary locations include:- Oil Refineries – Tanks store crude oil before processing.
- Oil Terminals – Intermediate storage before transportation via pipelines, ships, or trucks.
- Production Sites – Located near oil wells or offshore platforms for temporary storage.
- Strategic Petroleum Reserves (SPR) – Government reserves for emergency supply security.
Types of Crude Oil Storage Tanks
Let's explore the world of storage tanks, focusing on the eight main types used for liquid storage:
1. Fixed-Roof Tanks:
- Description: These are the most common and generally the least expensive type of storage tank. They consist of a cylindrical steel shell with a permanently attached roof, which can be cone-shaped or dome-shaped.
- Key Features: Simple design, low construction cost.
- Limitations: Vapor space above the liquid is directly exposed to the atmosphere, leading to potential evaporation losses and emissions. Older tanks might not be vapor-tight due to riveted or bolted construction. Modern tanks are typically welded for a leak-free seal.
- Usage: Suitable for liquids with low volatility and where vapor emissions are not a major concern.
2. External Floating Roof Tanks:
- Description: These tanks have an open top and a roof that floats on the surface of the liquid. The roof rises and falls with the liquid level.
- Key Features: Reduces vapor space and thus evaporation losses compared to fixed-roof tanks.
- Limitations: The floating roof is exposed to the elements, making it susceptible to rain, snow, and wind. Requires a robust seal between the roof and the tank shell to prevent vapor leaks.
- Usage: Used for storing large volumes of liquids, especially those that are more volatile than those stored in fixed-roof tanks.
3. Internal Floating Roof Tanks:
- Description: Similar to external floating roof tanks, but with a fixed roof over the floating roof.
- Key Features: Combines the reduced evaporation of a floating roof with the weather protection of a fixed roof.
- Limitations: More complex and expensive than external floating roof tanks.
- Usage: Suitable for storing volatile liquids where minimizing emissions is crucial.
4. Domed External Floating Roof Tanks:
- Description: A hybrid design combining an external floating roof with a dome-shaped roof covering it.
- Key Features: Offers even better protection from the elements compared to standard external floating roof tanks.
- Limitations: Higher cost and complexity compared to other floating roof tank designs.
- Usage: Used when environmental regulations are stringent or when storing particularly sensitive liquids.
5. Horizontal Tanks:
- Description: Cylindrical tanks with the axis oriented horizontally.
- Key Features: Can be installed above or below ground. Simpler construction for smaller capacities.
- Limitations: Not economical for very large storage volumes.
- Usage: Used for storing a variety of liquids, including fuels, chemicals, and water. Common in smaller-scale applications.
6. Pressure Tanks:
- Description: Designed to hold liquids under pressure. They can be spherical or horizontally oriented.
- Key Features: Robust construction to withstand internal pressure.
- Limitations: More expensive due to the higher design and construction standards.
- Usage: Used for storing liquefied gases (like propane or butane) or other liquids that require pressure to remain in a liquid state.
7. Variable Vapor Space Tanks:
- Description: These tanks are designed to accommodate the expansion and contraction of vapors due to temperature changes. They can be cylindrical or spherical.
- Key Features: Minimize vapor releases to the atmosphere.
- Limitations: More complex than standard fixed-roof tanks.
- Usage: Used for storing volatile liquids where vapor emissions need to be carefully controlled.
8. LNG (Liquefied Natural Gas) Tanks:
- Description: Specialized tanks designed to store LNG at cryogenic temperatures.
- Key Features: Heavily insulated to maintain extremely low temperatures. Complex safety systems.
- Limitations: Very expensive due to specialized materials and construction.
- Usage: Exclusively used for storing LNG.
General Notes on Tank Construction:
- Welding: Modern storage tanks are typically fully welded to ensure a leak-free and vapor-tight seal.
- Riveting/Bolting: Older tanks often used riveted or bolted construction, which can be more prone to leaks. These are less common in modern applications.
- Above/Below Ground: The first four tank types listed (fixed-roof, floating roof) are almost always above ground. Horizontal tanks can be either above or below ground. Pressure tanks are typically above ground.
There are different types of tanks based on storage needs and construction:
- Fixed Roof Tanks – Used for low-volatility crude oil; comes with a vent system.
- Floating Roof Tanks – Designed for volatile crude oil; reduces vapor loss.
- Dome Roof Tanks – A variation of fixed roof tanks with an aluminum dome for added protection.
- Bullet Tanks – Horizontal, pressurized tanks for specific crude storage applications.
- Underground Storage – Used in strategic reserves, reduces environmental risks.
Specifications of Crude Oil Storage Tanks
The specifications of crude oil tanks depend on design standards and requirements:Material
- Carbon Steel – Common for atmospheric storage tanks.
- Stainless Steel – Used for corrosive crude oil.
- Fiberglass-Reinforced Plastic (FRP) – Used in some applications to resist corrosion.
Capacity
- Small tanks: 1,000 – 50,000 barrels
- Large tanks: Up to 500,000 barrels
- Strategic reserves: Millions of barrels
Design Standards
- API 650 – Standard for atmospheric oil storage tanks.
- API 620 – Standard for low-pressure tanks.
- API 12F – Specification for field-welded tanks.
- ASME Section VIII – Pressure vessel design.
Safety Features of Crude Oil Storage Tanks
Safety is a critical aspect of crude oil storage due to fire, explosion, and environmental risks.Function of Breather Valve on Petroleum Tank
 |
| Breather Valve |
A breather valve, also known as a pressure-vacuum valve, is a safety device commonly found on storage tanks with fixed roofs. Its purpose is to allow the tank to operate under a slight internal pressure or vacuum. This helps to prevent the tank from being damaged by overpressure or implosion.
Structural Safety
- Secondary Containment – Dikes or bund walls prevent oil leaks from spreading.
- Emergency Vents – Release pressure to prevent tank rupture.
- Seismic Protection – Designed to withstand earthquakes in high-risk zones.
Fire Protection
- Foam Fire Suppression Systems – Extinguish fires using foam blankets.
- Water Sprinkler Systems – Cools tanks during emergencies.
- Explosion-Proof Venting – Prevents tank overpressure.
Environmental Protection
- Leak Detection Systems – Sensors to identify leaks.
- Floating Roofs – Minimize vapor emissions.
- Vapor Recovery Systems – Capture and process hydrocarbon vapors.
Operational Safety
- Level Monitoring Systems – Prevents overfilling.
- Automatic Shutoff Valves – Stops oil flow during emergencies.
- Lightning Protection Systems – Reduces fire risk from lightning strikes.
