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Detailed Comparison Between API 650, API 620, EN 14015

A detailed analysis and comparison of three key standards in the field of storage tank construction and design — API 650, API 620, and EN 14015 — provides essential insights into the world of structural engineering. These standards, developed by the American Petroleum Institute (API) and the European Committee for Standardization (CEN), respectively, outline the comprehensive guidelines and protocols that engineers around the world use to design, construct, and maintain safe and efficient storage tanks for various purposes.

API, established in 1919, is an American trade association promoting the interests of the oil and natural gas industry, while also providing technical standards and certifications. API 650 and API 620 are among their most recognized standards, focusing on oil storage tank design.

EN 14015, on the other hand, is a European standard. The CEN was founded in 1961 to remove trade barriers for European industry and consumers. It is responsible for developing and defining voluntary standards at the European level.


API 650 outlines the standards for designing and constructing welded oil storage tanks. The standard covers the design, fabrication, erection, and inspection of steel storage tanks, ensuring they're safe, reliable, and meet the requirements for storing crude oil and other petroleum products. Its primary focus is tanks that operate at atmospheric pressure or at a very slight pressure.

The range of operating temperature in tanks designed under this standard spans from -40°F to 500°F. The standard acknowledges a variety of materials for construction, with carbon steel being the most common. Other weldable materials are also allowed, depending upon the storage conditions and the type of product stored.

The tanks are predominantly cylindrical in shape, featuring either a flat or slightly sloped bottom. API 650 considers open-top or fixed-roof tanks (such as cone or dome roof tanks) and even those with a floating roof. The standard incorporates rigorous criteria for designing, welding, constructing, and inspecting the tank's elements, including the bottom, shell, and roof.

API 650 pays detailed attention to the design considerations for environmental effects, particularly for wind and seismic conditions. It provides robust guidelines for normal and emergency venting requirements. Also, API 650 mandates leak testing to ensure the integrity of the tank.

API 620 provides the standards for designing and constructing large, welded, low-pressure storage tanks. These tanks are ideal for storing gases and high-volatile liquids at lower pressures, i.e., up to 15 PSI. This standard is often utilized for tanks storing liquefied natural gas (LNG) and other cryogenic substances.

The temperature range for tanks under API 620 spans from -325°F to 250°F. While carbon steel is a popular choice under API 620, it permits a wider range of materials, including nickel and stainless steel. The tanks are usually cylindrical with a flat or conical bottom and a spherical or cylindrical roof.

Like API 650, API 620 takes environmental factors into account, covering not only wind and seismic conditions but also snow loads. The standard provides detailed specifications for foundation designs, such as reinforced concrete, pile, or mat foundations.

The inspection and testing under API 620 are stringent. It mandates radiographic testing for all vertical and horizontal butt welds to ensure the integrity of the tank's structure. Venting requirements are similar to API 650, and leak testing is a prerequisite.

EN 14015 sets out the standards for vertical, cylindrical, flat-bottomed, above-ground, welded steel tanks. These tanks are used for storing liquids at ambient temperature and above.

The standard doesn't specify a range for operating temperature, but it's generally understood to be suitable for ambient and higher temperatures. The primary materials for these tanks are carbon and stainless steel, but other materials can be utilized depending upon the requirements.

The tanks under EN 14015 are designed as vertical and cylindrical with a flat bottom. The roof can be either fixed or floating, depending upon the stored material and other design considerations.

EN 14015 considers several environmental factors like wind load, seismic conditions, and snow load. The standard requires the tanks to be installed on a good quality level and flat surface. Inspection and testing are rigorous and include radiographic and ultraviolet testing.

The comparison between these three standards provides a comprehensive understanding of the diverse factors influencing the design, construction, and maintenance of storage tanks. However, it's worth noting that these are intricate and comprehensive documents and should be thoroughly reviewed and correctly applied when designing or constructing a storage tank. Moreover, as these standards are updated periodically, the most recent versions should be referred to ensure compliance with the latest requirements.

In conclusion, while these standards provide an invaluable resource for engineers, they should be viewed as guides rather than strict instruction manuals. The unique nature of each project demands a careful analysis and application of these standards, often requiring expert judgment to optimize the design. As such, professional help should be sought when designing or constructing storage tanks under these standards. This approach ensures safety, efficiency, and adherence to the most relevant and up-to-date international standards.



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