Where is the maximum allowable working pressure (MAWP) of a vessel defined?

The maximum allowable working pressure (MAWP) of a vessel is defined at the top of the vessel. This designation is crucial for understanding the operational limits of pressure vessels, as it indicates the highest pressure that the vessel can safely handle under specified conditions.

The MAWP is typically determined during the design phase of the vessel and is influenced by factors such as material selection, the design of joints and welds, and the geometry of the vessel. Since pressure in a vessel tends to increase towards the top due to buoyancy and hydrostatic forces, establishing the MAWP at the top ensures that safety margins are considered for operational scenarios that might lead to higher pressure accumulation, especially in processes where gas is involved.

While various parts of the vessel may experience pressure to some extent, defining the MAWP at the top provides a clear and conservative measure for safe operation under operating conditions, ensuring better protection against potential failures due to pressure build-up.