Better be careful here and use the proper definitions. The design pressure is the maximum allowable working pressure (MAWP)of the boiler based on ASME Boiler and Pressure Vessel Code. What does this mean? By definition in Section I, Note (9) MWAP is the maximum pressure and temperature conditions that could be sustained above normal operating conditions (working pressure). Please review ASME Boiler and Pressure Vessel Code, Section I, PG-21.