What is the required minimum size for bottom plates or annular plates as per API 650?

• A. No specific size requirement
• B. They must match the diameter of the tank
• C. They should be large enough to support at least 2 inches beyond the shell
• D. They should be equal to the base area of the tank

Answer: (C)

The correct answer highlights that the minimum size for bottom plates or annular plates must be sufficiently large to extend at least 2 inches beyond the base of the shell. This requirement is essential for several reasons. First, it ensures that there is adequate support for the tank's weight and the contents it holds, which is critical for stability and safety. By extending beyond the shell, the plates help distribute the load more evenly, which can prevent stress concentrations that might lead to structural failure over time.

Additionally, the extra length provides a margin for any potential movement or settling of the tank. It also offers some protection against environmental factors, such as erosion or corrosion, which could impact the integrity of the tank if the base is too narrow. Adhering to this requirement helps ensure compliance with safety standards set forth by API 650 and enhances the longevity and effectiveness of the storage tank.