The accurate definition of MAWP? 1

[etsen]

MAWP means the maximum allowable gauge pressure at the top of the vessel at the design temperature in GB150-1998 Steel Pressure Vessel in China. But I can't really get it. Why does maximum allowable working pressure(MAWP) occur at the top of the vessel? Could anyone please explain it? And is there any accurate definition in other standards or codes? Thanks.

 

[prex]

At top simply because design pressure and MAWP do not include any liquid head: it is up to the designer to account for local pressures at different locations in a (tall) vessel.
The definition in UG-98 of ASME VIII Div.1 is complete and accurate.

prex

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[gr2vessels]

etsen,
when you design a pressure vessel, you have to make sure that every component of that equipment will withstand all the design loads you have specified. In accordance with any pressure vessel code in the world, the weakest component is the least loaded component of that vessel, but not less than the design pressure. The only component(s) designed for the design pressure are in the top of the vessel;- all the rest of the components have to include additional pressure due to the static head of the liquid (if present). Try to imagine what IS THE SAFEST pressure not exceeding the design pressure you can operate the vessel without risking to kill someone. That is the Maximum Allowable Operating Pressure, which can be higher than the design pressure if you opted to use better, stronger and thicker materials than you have calculated for the minimum requirements. Otherwise, you must use the lowest pressure you designed the vessel for, which is the Maximum Allowable Operating Pressure in the top of the vessel.
Hope this helps,
cheers,
gr2vessels

 

[davefitz]

In most cases, the pressure relief valves are located at the top of the vessel, and their set pressure is set at MAWP, and the MAWP is listed on the boiler's nameplate and controlling documents. So, an inpsector and any other concerned person can easily check if you have the correct rated relief valves on the boiler.

The design of the piping and pressure vessels at lower elevations must include add'l strength for th eadd'l hyddrostatic head due to lower elevations, if containing a dense liquid.