What is the difference between MAWP(maximum allowable working pressure) and MAP (Maximum allowable pressure). What does this sentence meant for, "The maximum pressure in normal operating position at teh top."

Please Advoce.

ASME Code Section VIII Division 1 defines MAWP in Appendix 3. The MAWP (Maximum Allowable Working Pressure) for the pressure chamber is the maximum pressure that can be sustained at the top of the chamber such that no component is overstressed. This is based on allowable stresses at the design temperature, vessel in corroded condition, with operating liquid accounted for.

MAP (Maximum Allowable Pressure) is not explicitly defined in Appendix 3. But most organizations I have dealt with consider this to be the maximum pressure that can be sustained in the new condition, allowable stresses at ambient temperature, and without any operating liquid.

Actually, the MAP by this definition is the same as the "basis for calculated test pressure" per UG-99(c). See the definition of "calcuated test pressure" in Appendix 3.

This point accounts for the additional pressure due to the liquid level that may exist in the vessel during operation. The pressure components below the liquid level will be subjected to the pressure at the top of the vessel plus the additional pressure due to the hydrostatic head of the operating liquid.

For example, let's say that the pressure chamber's MAWP is 100 psi as governed by the bottom head, and that there is no operating liquid. Now if the vessel operation is reconfigured such that there is an operating liquid and the pressure on the bottom head due to this liquid is 12 psi, then the pressure chamber MAWP must be reduced: 100 - 12 = 88 psi. Otherwise, if you consider the 100 psi original MAWP + 12 psi liquid pressure the head would be overstressed.

I have actually been asked about this a number of times. A designer will design a vessel for a particular pressure that is same as the pressure rating for, say, a Class 300, etc, flange. Then they add a liquid level and the flange is no longer "good" and they wonder why. This is because the pressure that the flange now is subjected to is greater than its pressure rating.

You are reducing the MAWP of the vessel in case of operating liquid just to balance out the syetem with no operaating liquid. This makes no sense, please explain in reference to code.

Now Mr. Tom

"with opearing liquid accounted for" This mean static head, please reply. Also, elaborate in context of horizontal and vertical equipment seperately.

best regards

ikram

Ikrama

According to the defination MAWP is the maximum pressure sustained at the top of chamber which no overstress components i.e. resultant MAWP should be subtracted with the static head and same is beine explained by tom i.e. MAWP is calculated accounting operating liquid.

That means it should be subtracted in final calculations

Bye

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Syed Osama Nusrat Ali
Exective Engineering (Project)
Fauji Fertilizer Company Limited
Pakistan
email: osama_ali@ffc.com.pk
Cell # +92-3025252018