Calculated MAP, MAWP and Test Pressures

Defenition :

1. Maximum Allowable Working Pressure ( MAWP) ( units : Psi).

The MAWP for a vessel is the maximum permissible pressure at the top of the vessel in its normal operating position at the specific temperature, usually the design temperature.

The MAWP is the maximum pressure allowable in the "hot and corroded" condition. It is the least of the values calculated for the MAWP of any of the essential parts of the vessel and adjusted for any difference in static head that may exist between the part considered an the top of the vessel.

This pressure is based on calculation for every element of the vessel using the nominal thickness exclusive of corrossion allowance. it is the basis for establishing the set pressure of any pressure-relieving devices protecting the vessel. The design pressure may be substitude if the MAWP is not calculated.

The MAWP for any vessel parts is the maximum internal or external pressure, including any static head, together with the effect of any combination of loading listed in UG-22 which are likely to occur, exclesive of corrosion allowance at the designated coincident operating temperature. The MAWP for the vessel will be governed by the MAWP of the weakes parts.

2. Maximum Allowable Pressure ( MAP) ( units Psi).

The term MAP is often used. it refers to the maximum permissible pressure based on the weakest part in the new ( uncorroded) and cold condition, and all other loadings are not taken into consideration.

3. Design Pressure ( DP) (units Psi)

The pressure used in the design of a vessel component for the most severe condition of coincident pressure and temperature expected in normal operation. there is a maximum design temperature and minimum design temperature for any given vessel.

The minimum design temperature would be the MDMT, as the lowest allowable temperature for vessel under external pressure shall not exeeds the maximum temperatures given on external pressure charts.

4. Operating Pressure

The pressure at the top of the vessel at which it normally operates. it shall be lower than the MAWP, design pressure, or the set pressure of any pressure relieving device.

5. Operating Temperature

The temperature that will be maintained in the metal of the part of the vessel being considered for the specified operation of the vessel.

Calculations :



 MAWP, corroded at Design Temperature Pw :

Notes :

1. also check pressure - temperature rating of the flanges for MAWP and MAP.
2. All nozzles should be reinforced for MAWP.
3. The MAP and MAWP for other components , i.e. cones, flat heads, hemi-heads, torispherical heads, ect, may be checked in the same manner by using the formla for pressure found in procedure.


Source :

Pressure Vessel Design Manual 3E - Dennis R Moss