Design Pressure and Maximum allowable Working Pressure (MAWP) of the Boiler

The Design Pressure of the boiler is the maximum pressure at which the boiler can be operated under normal operating conditions.  It is equal to the highest setting of the safety valves in the boiler.

For instance, if a boiler has two safety valves, the design pressure will be equal to the setting of the valve with the higher setting.

The design pressure is calculated based on the stress that the boiler will undergo during operation across its lifetime.

Maximum Allowable Working Pressure
This is the maximum pressure that the boiler can withstand.  The maximum allowable working pressure is calculated based on the strength of the material, the thickness of the walls, etc.

The Design Pressure of the boiler is lesser than or equal to the Maximum Allowable Working Pressure.