Under which condition would you add 15°F to the temperature during design calculations?

• A. For high design temperatures
• B. When determining maximum metal temperature
• C. If requesting the lowest design temperature
• D. For summer temperature calculations

Answer: (C)

In design calculations for welded tanks, particularly as outlined in API 650, the addition of 15°F is specifically applicable when determining the lowest design temperature. This practice helps to ensure that the structural integrity of the tank can withstand temperature variations that may occur during real operating conditions.

When calculating the lowest design temperature, it is crucial to account for potential fluctuations that may cause the materials to behave differently than expected at nominal temperatures. The additional 15°F acts as a safety margin, helping to prevent issues such as brittle failure or other material vulnerabilities that may arise due to colder conditions than those anticipated.

This specific adjustment is a standard practice in the design of storage tanks to ensure reliability and safety under various environmental conditions. Thus, the proposed answer recognizes an important aspect of temperature management within the context of tank design as per API standards.