Oil storage tanks serve as a staging area to collect crude oil in several stages of production. These tanks are used in production fields and hold the oil until it is delivered to tankers or into a pipeline. Storage tanks are also used as a holding area for crude oil before the refining process and they also hold refined products after it is processed. While they are used for an array of purposes throughout the industry, the overall design and functionality of storage tanks is similar across the board.
What Types of Storage Tanks Are There?
Storage tanks typically fall under two major classification: pressurized storage tanks and atmospheric storage tanks. Pressurized storage tanks are generally used for liquids that evaporate, while atmospheric tanks are operated at a pressure at or close to the pressure of the atmosphere. Atmospheric storage tanks are used for the storage of oil and are further broken into several based on different designs of fixed and floating roofs. The type of roof on your storage tank should be selected based on the flash-point of the liquid that is being stored.
Fixed Roofs
Fixed roofs are suitable for fuel oil, water, or any liquid that has a very high flash point and is not volatile. Fixed roofs are either vented or have a breather valve that allows the tank to operate with a small amount of internal pressure. Fixed roofs can be further classified into the following types of designs.
Types of Fixed Roofs:
- Cone Roof
- Umbrella Roof
- Dome Roof
What Considerations Should be Made in Selecting a Storage Tank?
After deciding what type of storage tank, you will want to take careful consideration into the sizing of the tank(s). There are several parameters to keep in mind when determining the tank size needed. The batch arrival, or the frequency at which the crude arrives, and the cycle time in between the arrival of those batches. You will also need to consider the tank bottom or the volume at the bottom of the tank that is not accessible and finally, the safe-fill allowance needs to be considered, which is the safety factor to keep the tank from overflowing.
Next, you will want to consider the location of your storage tanks. Tanks are often built and used in groups, also known as tank batteries, and the placement of the tank battery is important to make sure that that there is adequate spacing between tanks and the proximity to any hazardous material is considered. Some tank batteries are connected to just one well, while others receive and process fluids from several different wells. Therefore, a tank battery will need to be equipped to handle the different requirements for each well.
It is important to make sure that your tank battery is placed in accordance with the flammable and combustible liquids code. NFPA 30 minimum requirements are dependent on the medium being store and at what temperature and pressure. For more information on these regulations, reference the NFPA 30 Flammable and Combustible Liquids Code.
What is an API Certification?
The American Petroleum Institute maintains standards, recommended practices and certifications for oil and gas equipment. There are several specifications that apply to storage tanks, with each standard specific to different types of tanks. These specifications allow for standard practices for the manufacturing, inspecting, and maintaining of storage tanks. The most common standards are as follows:
API-650: Welded Steel Tanks for Oil Storage
This specification was created based on recommendations and experiences from both manufacturers and purchasers of welded oil storage tanks of various sizes and capacities for internal pressures not more than 2.5 psi. For more information the API-650 standard.
API-620: Design and Construction of Large Welded Low-Pressure Storage Tanks
This specification was created based on recommendations and experiences from both manufacturers and purchasers of welded, low-pressure oil storage tanks of various sizes and capacities for internal pressures not more than 15 psi. For more information the API-620 standard.
The API 12D: Specification for Field-welded Tanks for Storage of Production Liquids
This specification was created based on recommendations and experiences from both manufacturers and purchasers of field-welded steel storage tanks of various sizes and capacities for internal pressures approaching atmospheric. For more information the API-12D standard.
The API 12F: Specification for Shop Welded Tanks for Storage of Production Liquids. This specification was created based on recommendations and experiences from both manufacturers and purchasers of welded steel shop-fabricated storage tanks. For more information the API-12F standard.
Regarding the specific dimensions, design standards, and compatible medium requirements of the storage tank, you can contact us directly to obtain a customized specification plan, helping you select the right model accurately.
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FAQ
Q: How do crude oil storage tanks work?
A: Upon being introduced into a storage tank at above atmospheric pressure, crude oil and condensate experience pressure drops which cause gases dissolved in the liquid to vaporize or 'flash' out of the liquid phase and collect in the vapor space between the liquid and the fixed roof of the storage tank.
Q: What is the capacity of a crude oil storage tank?
A: Crude Oil Storage Tank Capacity: Crude oil storage tanks can hold a range from 50,000 to millions of barrels of oil, with sizes often detailed in a crude oil storage tank size chart, like the one shown here.
Q: Do I need planning permission for an oil tank?
A: As of 2022, you won't need planning permission as long as: Your tank does not exceed a 3500-litre capacity. Your tank isn't being stored in front of the main elevation fronting a public road. The height of your tank is not greater than 3 metres.
Q: What is the life expectancy of an oil storage tank?
A: around 20-25 years
While they can last several decades if very well-maintained, most modern oil tanks have a functional lifespan of around 20-25 years, or thereabouts. Older tanks are increasingly prone to corrosion, fatigue and problems if not treated with the proper maintenance and upkeep that they need to continue working.
Q: Why do oil tanks have floating roofs?
A: Floating roofs are made of a structure which floats on the surface of the liquid in order to prevent the formation of a gas overhead, and thus reduces: Fire risks. Atmospheric pollution. Evaporation losses.