or any other type of boiler the drum 10 is of an elongated cylindrical shape and has a wall 12 that is penetrated by nozzles 14 that receive a high temperature steam liquid mixture and discharge this mixture into an annular space 16 between a drum liner or baffle 18 and an inner surface 15 of the wall 12 the wall 12 also has an exterior surface 17 the nozzles 14 may extend beyond the inner surface 15 of the wall fig2 or they may terminate at the inner surface 15 fig3 a liquid 26 such as for example water pools in the bottom of the drum 10 one or more steam separating units 24 are located outside the volume enclosed by the baffle 18 steam from the steam liquid mixture 34 and from the vaporization of the water 26 passes through a drying assembly 32 and is removed through an outlet 30 the configuration of fig2 is not limited to that as shown as other configurations are possible upon operation of the boiler particularly at startup from ambient conditions the nozzles 14 and the areas 15 a of the inner surface 15 of the wall 12 surrounding the nozzles 14 are affected by the steam liquid mixture 34 temperature transients e g the movement of heat from one area to another through the materials of the nozzles 14 and the wall 12 produce thermal stresses accordingly the nozzles 14 and the areas 15 a surrounding the nozzles namely the drum wall 12 and.