The MAWP is determined based on:

• A. Weakest component at design temperature
• B. The component with the highest allowable stress
• C. The thickest section of the vessel
• D. The most restrictive component at design temperature

Answer: (D)

MAWP is set by the component that imposes the lowest allowable pressure when everything is evaluated at the design temperature. Each part of the vessel—shell, heads, nozzles, welds, reinforcements—has an allowable stress at the design temperature, which, together with its geometry, determines how much pressure it can safely carry. The part with the smallest allowable pressure becomes the limiting, or most restrictive, component, and that value controls the overall MAWP.

The option describing the most restrictive component at design temperature captures this idea exactly. The vessel isn’t limited by the thickest section or by the part with the highest allowable stress—those wouldn’t set the safety limit. The term “weakest” is related, but the key point is that the governing factor is the component whose rating at the design temperature is lowest.