Flange pressure-temperature rating generally behaves?

• A. Decreases with Temperature
• B. Remains Constant with Temperature
• C. Oscillates with Temperature
• D. Increases with Temperature

Answer: (D)

Flange pressure-temperature ratings are driven by how material strength and joint sealing performance change with temperature. As temperature rises, the allowable stress in flange material (and in bolts) generally decreases due to reduced yield strength and increased creep tendencies. The gasket and bolt behavior is also affected by heat, which can alter preload and seating effectiveness. Because of these effects, the maximum permissible pressure at higher temperatures is lower than at room temperature, so the rating Derates with increasing temperature. In practice, you use the P-T charts from ASME B16.5 (and related standards) to see how the allowable pressure drops as temperature climbs, ensuring the joint remains safe and leak-free under elevated temperatures.