As defined in UG-98 of the Code, the Maximum Allowable Working Pressure (MAWP), is the maximum pressure permissible at the top of the vessel in its normal operating position. It is the least of the values calculated for each of the vessel part adjusted for the static head and by including the effect of any combination of loadings listed in UG-22 of the Code.

Conventional method of calculating the MAWP is to consider only the main pressure parts viz., the shells and the heads and the significant UG-22 loading viz., the wind and the seismic. Once the MAWP is determined, the rest of the vessel design is completed considering this value of MAWP as design pressure combined with any other applicable UG-22 loading. At the end, the vessel is verified for its adequacy to the test condition.

It is noted that, the MAWP obtained through this method is often higher than the design pressure thus leading to the overdesign of the vessel. Moreover, higher MAWP results in higher test pressure, which might have a considerable impact of its own on the design of the vessel.

The objective of this paper is to propose a design approach in which the test pressure itself is included as one of the governing loads in the determination of the MAWP so that the impact on vessel design, as explained above, is minimized.

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