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API Standard 650: Basic requirements for the design and construction of petroleum storage tanks

October 29, 2025
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API 650, developed by the American Petroleum Institute (API), is one of the most authoritative and widely used standards worldwide for the design and construction of storage tanks for crude oil and petroleum products. This standard comprehensively defines the technical requirements for the construction of welded steel tanks of varying capacities (from 20 to 300 feet in diameter). This article provides an overview of the standard’s content, application, and significance.

1. Scope of the API 650 standard

1.1 Coverage area

  • Storage tanks of varying capacities

  • Storage tanks with an internal pressure of up to 2.5 psi.

  • Operating temperature range: -50 to 500 degrees Fahrenheit

  • Various petroleum products, including crude oil, gasoline and diesel fuel.

1.2 Exceptions

  • High-pressure storage tank (over 2.5 psi)

  • Storage tanks with extremely high operating temperatures

  • Tanks with unusual or special shapes

2. Basic design requirements based on API 650

2.1. Calculation of sheet thickness

  • One-leg method

  • Method for design with a variable number of points

  • Considerations on hydrostatic pressure

  • taking into account the effects of wind and earthquakes

2.2 Welding and Joining

2.3. Key Considerations

  • Select the appropriate steel sheet (ASTM A36, A283, A573, etc.).

  • Seals and sealing materials

  • Interior and exterior protective coatings

3. Main components of the tank according to API 650

3.1 Basic structure

  • Foundation and institution

  • motherboard

  • Shell share prices

3.2. Undershirt

  • Solid ceiling

  • Floating roof

  • domed roof

3.3 End devices

  • Drain cover

  • Inlet and outlet pipes

  • ventilation system

  • Liquid level gauges

4. Phases of tank construction according to API 650 standard

4.1 Preparation

  • Raw material testing

  • Transcript

  • Sheet metal casting

4.2 Assembly

  • Laying floor coverings

  • Complete body

  • Ceiling mounting

  • Butt welding

4.3 Testing and Inspection

5. Advantages of API 650 compliance

5.1 Technological advantages

  • It offers a very high level of safety and is resistant to leaks and damage.

  • long service life of the fuel tank

  • It proves its reliability under a wide variety of conditions.

5.2 Economic advantages

  • Reducing maintenance costs

  • Improvement of raw material consumption

  • It enjoys a high reputation worldwide and has a simplified approval process.

5.3 Environmental benefits

  • Reducing the risk of oil spills

  • Improved steam control

  • Waste management

6. Differences between API 650 and other tank standards

6.1     Compared to API 620

  • Working pressure range

  • Design method and calculation

  • Materials used

6.2     Compared to ASME Section 8

  • Multiple applications

  • Design details

  • Verification requirements

6.3. Comparison with the European standard (EN 14015)

  • Calculation method

  • Requirements for the materials

  • Security measures

7. Inspection and maintenance of storage tanks according to API 650

7.1 Inspection plan

  • Initial examination

  • Regular   inspection  

  • Post-repair inspection

7.2 Test methods

  • Visual inspection (VI)

  • Magnetic particle testing

  • Penetration tests (PT  )

  • Ultrasound examination (US)

7.3 Preventive maintenance

  • Wall thickness control

  • Checking the protective layer

  • Control of the cathodic corrosion protection system

8. Latest Standard Updates

Version 8.1.2020

  • Changes in thickness calculation

  • Updated  welding requirements

  • New considerations regarding environmental pollution

8.2 Future Changes

  • More attention to environmental issues

  • Convergence of digital technologies

  • Improved corrosion assessment methods

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9. Problems with the implementation of the API 650 standard

9.1 Technical Problems

  • The materials are supplied in accordance with the standards.

  • Experienced building contractors wanted

  • Precise execution of thin welds

9.2 Economic problems

  • Strict adherence to this rule is extremely costly.

  • Modern testing equipment is required.

  • Costs for employee training

10. Industrial Applications of API 650

10.1 Oil and gas industry

10.2 Chemical Industry

  • Storage of   chemicals

  • Intermediate tank

  • Storage of petrochemical products

10.3 Other industries

  • power plant

  • gas station

  • military installations

Finally

API 650 is a     comprehensive and practical document that      plays a key role in the safety and reliability of crude oil storage tanks. Compliance with this standard offers the following benefits:

  1. High safety     : Reduces the risk of accidents and material leaks.

  2. Long service life     : optimized for long-term use.

  3. Global recognition     : Can be used in international projects.

  4. Economic advantages     : reduced maintenance costs.

Recommendations for petroleum engineers and project managers:

  • Find out about the latest version of the standard.

  • Appointment of experienced consultants to implement the standard.

  • Implement a regular inspection plan.

  • Inform employees about the standard requirements.

Due to technological advances, the API 650 standard is expected to evolve further to meet the complex requirements of the oil and gas industry.