What is the minimum film clarity required for vertical welds when the plate thickness is greater than 1 inch?

• A. 2 inches of vertical weld
• B. 3 inches of vertical weld and 1 inch of horizontal weld
• C. 3 inches of vertical weld and 2 inches of horizontal weld
• D. 1 inch of vertical and horizontal weld

Answer: (C)

The correct choice pertains to the clarity requirements for vertical welds in the context of API 650, particularly when dealing with thicker plates. When the thickness of the plate exceeds 1 inch, the specification requires a minimum of 3 inches of vertical weld clarity along with an additional 2 inches of horizontal weld clarity. This requirement ensures that the welds can effectively handle the stresses and loads associated with large storage tanks and can contribute to the structural integrity and safety of the installation.

The emphasis on both vertical and horizontal clarity indicates the critical nature of weld quality in areas where stress concentrations are likely to occur. Having a robust weld profile helps to mitigate the risks of defects that could lead to failures under operational conditions.

In contrast, the other options either provide insufficient weld clarity or do not meet the specified requirements for thicker plates as mandated by the standard, hence do not align with the guidelines set forth in API 650 for such applications.