Relationship Between Design Pressure & Maximum Allowable Working Pressure (MAWP)

Maximum Allowable Working Pressure (MAWP)

Maximum gauge pressure permissible at the top of a completed vessel in its normal operating position at the designated coincident temperature specified for that pressure. MAWP is the least of the values for the internal or external pressure as determined by the vessel design rules for each element of the vessel using actual nominal thickness, exclusive of additional metal thickness allowed for corrosion and loadings other than pressure. The MAWP is the basis for the pressure setting of the pressure-relief devices that protect the vessel.

Design pressure

A pressure with coincident design temperature, used to determine the minimum permissible thickness or physical characteristic of each component, as determined by the design rules of the pressure-design code. The design pressure is selected by the designer to provide a suitable margin above the most severe pressure expected during normal operation at a coincident temperature. The design pressure is equal to or less than the Maximum Allowable Working Pressure (MAWP).

Design Pressure <= MAWP

Note :
Design pressure is normally the Pressure Relief Valve (RV) set pressure of a vessel. This pressure at coincident temperature is used to determine the minimum wall thickness. A calculated thickness is 9 mm based on a design pressure @ coincident temperature. However, with a standard material thickness of 10 mm. The MAWP would be calculated pressure based on this thickness.