API 650 standard : Welded Tanks for Oil Storage

API Standard 650, also known as “Welded Tanks for Oil Storage”, is a well-recognized standard developed by the American Petroleum Institute (API) that outlines the guidelines for the design, fabrication, erection, and inspection of welded steel tanks for oil storage. The standard is comprehensive, covering various aspects including material selection, design criteria, welding procedures, and inspection and testing requirements to ensure the safety and integrity of the tanks.

Key aspects of API 650 include:

1. Material Selection: The standard specifies that tank shells should be constructed from carbon or low alloy steel with a maximum carbon content of 0.21% to ensure adequate strength, toughness, and resistance to corrosion​​.
2. Design Criteria: API 650 provides formulas for calculating the minimum required thickness of the tank’s shell, bottom, and roof plates based on design stress, corrosion allowance, and other factors such as the hydrostatic test pressure and maximum allowable working pressure (MAWP)​​.
3. Fabrication and Construction: The standard offers detailed guidance on welding procedures, non-destructive testing (NDT), and inspection during construction to maintain the quality and compliance of the storage tanks​​.
4. Inspection, Examination, and Testing: API 650 emphasizes the importance of periodic inspections, examinations, and testing to assess the tank’s condition throughout its service life, helping to identify and address potential issues before they become critical​​.
5. Impact Test Requirements: The standard mandates an impact test for materials’ weld metal, heat-affected zones (HAZ), and base metal if the Minimum Design Metal Temperature (MDMT) is lower than the lowest expected operating temperature, to evaluate the material’s toughness and resistance to fractures in low-temperature conditions​​.
6. Data Sheet Information: For the design of welded steel storage tanks, API 650 provides guidelines on what information should be included in a datasheet, such as general information, tank design data, material specifications, and details on welding and fabrication, among others​​.
7. Updates and Training: API 650 standards are periodically updated to incorporate industry advancements and safety improvements. Understanding the fundamentals of this standard is essential for professionals in mechanical engineering, inspection, maintenance, and operations related to storage tanks​​.

The API 650 standard, formally titled “Welded Tanks for Oil Storage,” is an extensively recognized guideline developed by the American Petroleum Institute. It provides comprehensive specifications for the design, construction, maintenance, and inspection of welded steel storage tanks used primarily in the oil industry. The standard ensures tanks are constructed safely and reliably, capable of storing various products at different pressures and temperatures.

Key components of the API 650 standard include:

1. Scope and Coverage: Defines the types of tanks and storage conditions the standard covers, including operational pressures and temperatures.
2. Material Specifications: Details the types of materials suitable for tank construction, focusing on strength, toughness, and corrosion resistance.
3. Design Criteria: Provides formulas and guidelines for determining the required thickness of the tank walls, roof, and bottom, accounting for various factors like product stored, internal pressure, wind load, and seismic considerations.
4. Fabrication Details: Outlines the welding procedures, joint designs, and construction practices to ensure the structural integrity of the tank.
5. Inspection and Testing: Specifies the inspection methods and testing procedures necessary to verify the tank’s conformance to the standard, including non-destructive testing (NDT) and hydrostatic testing.
6. Tank Appendages: Includes requirements for tank accessories such as nozzles, manways, vents, and ladders, ensuring their compatibility with the tank design and safety standards.
7. Markings and Documentation: Details the required documentation, data reports, and marking on the tanks to ensure traceability and compliance.
8. Annexes: The standard includes several annexes that provide additional guidelines on specific aspects such as seismic design, tank anchorage, and alternative designs for the tank bottom, roof, and shell.

This summary offers a high-level overview of the API 650 standard’s content. For comprehensive details, it’s recommended to refer to the actual standard document, which provides in-depth information on each section and aspect of tank design and construction. Professionals involved in tank design, construction, and maintenance typically refer to the full API 650 document for specific requirements and guidelines.

The latest version of the API Standard 650 is the 13th Edition, which was published in March 2020. This edition includes all amendments and changes up to January 2021. The API 650 standard provides comprehensive guidelines for the design, fabrication, erection, and inspection of welded tanks for oil storage, focusing on those with internal pressures approximating atmospheric pressure. It is applicable to tanks with a uniformly supported bottom and in non-refrigerated service with a maximum design temperature of 200°F or less. The standard is designed to ensure tanks provide adequate safety and reasonable economy for the storage of petroleum, petroleum products, and other liquid products​​​​.