What is the design temperature?

• A. Maximum Operating Temperature
• B. Minimum Ambient Temperature
• C. Maximum Metal Temperature Expected
• D. Temperature Limit Based On Material Yield

Answer: (C)

Design temperature is the highest temperature that the vessel’s metal is expected to experience in service, and it’s used to select the appropriate allowable stress from the code tables because material strength and properties change with temperature. This temperature refers to the metal itself, not the surrounding ambient or just the process outlet temperature. By establishing the maximum metal temperature, engineers ensure that the material will retain sufficient strength and toughness under the hottest conditions, including any heating in service and potential temperature rise. The other options don’t define the standard concept: ambient temperature isn’t the driver for the design of the pressure boundary, and while yield-related behavior affects allowable stress, the design temperature specifically targets the maximum metal temperature used in those calculations.