Under what condition are butt-welded annular bottom plates required?

• A. When using high-strength steel
• B. When the bottom shell course uses certain material groups
• C. When the tank diameter exceeds 40 feet
• D. When the bottom plates are thicker than 1 inch

Answer: (B)

Butt-welded annular bottom plates are required when the bottom shell course utilizes specific material groups outlined in the API 650 standard. This requirement ensures that the structural integrity of the tank is maintained, particularly at the critical junction where the shell and bottom plates meet. The use of butt welds is essential in these circumstances to provide adequate strength and prevent potential failures that can arise from the stress and loading conditions the tank will experience when in service.

For certain material groups, the mechanical properties may necessitate this type of weld connection due to factors such as yield strength, thickness, and overall design considerations. By using butt-welded seams, manufacturers can ensure that the weld's strength is compatible with the materials being utilized, thus enhancing safety and durability. This aspect is crucial in maintaining the functionality and reliability of the storage tanks, especially when they are subjected to various environmental factors and operational stresses.

The other conditions listed do not specifically trigger the requirement for butt-welded annular bottom plates in the same way as the material group stipulation does. Each of those scenarios has its own considerations but they do not necessarily dictate the need for butt welding in the context of annular bottom plate installation.