When a concrete ring wall is not provided, how level must the foundation be in any 10 ft of circumference?

• A. 1/4"
• B. 1/8"
• C. 1/2"
• D. 3/4"

Answer: (B)

A level foundation is crucial for the stability and integrity of welded tanks for oil storage. According to the standards set by API 650, when there is no concrete ring wall to provide support, the tolerances for the foundation's levelness become particularly stringent.

The requirement that the foundation must be level within 1/8" over any 10 ft of circumference ensures that the tank will properly distribute loads and maintain its structural integrity. This levelness helps prevent issues such as uneven settling, which can lead to stresses in the tank shell, instability, or potential failure of the tank over time due to environmental forces or operational pressures.

Maintaining this precise tolerance of 1/8" is critical for preventing problems related to uneven load distribution and can significantly influence the durability and performance of the tank. Other tolerances, while larger, would not adequately ensure the tank's stability, making the requirement of 1/8" the correct answer for the construction of a reliable tank foundation.