ASME VIII DIV 1 - MAWP at top of the vessel

[MohdYaseen2010]

ASME VIII DIV 1 Code stating that "the maximum allowable working pressure for a vessel is the maximum pressure permissible at the top of the vessel in its normal operating position at the designated coincident temperature specified for that pressure."
Where the highest pressure that the vessel can see in the bottom, not in the top? normally we should design for the most severe condition, Why the Code stating that the vessel MAWP should be measured at the top not in the bottom?

Mohd Yaseen

 

[david339933]

It is "designed" or maybe limited by the most severe condition....read the definition of MAWP 3-2 and UG-98.

 

[MohdYaseen2010]

According to (3-2), MAWP: is the maximum gage pressure permissible at the top of a completed vessel in its normal operating position at the designated coincident temperature for that pressure. This pressure is the least of the values for the internal or external pressure to be determined by the rules of this Division for any of the pressure boundary parts, including the static head thereon, using nominal thicknesses exclusive of corrosion allowances & considering the effects of any combination of loadings listed in UG-22 that are likely to occur (see UG-98) at the designated coincident temperature [see UG-20(a)]. It is the basis for the pressure setting of the pressure relieving devices protecting the vessel. The design pressure may be used in all cases in which calculations are not made to determine the value of MAWP.

Dear david339933 ;

From above statement (3-2), do you mean that the Code persist to use the least pressure calculated in order to safe the remaining of the weakest part.

Mohd Yaseen

 

[marty007]

Although the MAWP is calculated at the top of the vessel, the designer must still take into account the effects of additional loading on all components. If the vessel is filled with liquid for example, then the designer must design the components at the bottom of the vessel for a pressure equal to MAWP+liquid static head.

I think one of the reasons that MAWP is defined to occur at the top of the vessel is because this location is where most pressure relief and pressure indication equipment is installed. It allows for a direct comparison of MAWP vs. pressure relief valve settings without having to then take into additional effects of liquid static head.

Cheers,
Marty

 

[SnTMan]

Pressure at the high point of the vessel is unaffected by the nature or quantity of the contents. Suppose you were reading pressure off the bottom of a vessel whose fill level varied during operation.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[MohdYaseen2010]

Thanks Dears for your inputs;
I think we can conclude that considering the MAWP at Top of the vessel which is reflecting the least amount can be calculated for the MAWP among the vessel & consequently any relieve setting shall be based on this MAWP (the one calculated on the top), cause if we make relieve setting at MAWP(calculated in other location rather than top of the vessel), this will compel the vessel top portion to hazard.

Mohd Yaseen