Low pressure steam boilers are popular in many industries.  They provide fairly consistent temperature for the process without a complicated control system.  A low pressure boiler has maximum allowable working pressure of 15 psig as set by ASME Sect IV.  This means that the safety relief pressure must be fully open at a maximum of 15 psig.  This gives most LP steam boilers a maximum operating pressure of 12 to 13 psig.  The chart below shows the pressure//temperature relationship at these pressures.