PROBLEM TO BE SOLVED: To avoid or at least reduce a problem that atmospheric oxygen is introduced into a boiler water generated when pipes of a steam generator wall of a steam boiler wall of a power generation station in particular where carbon-containing fuel is combusted is filled with the boiler water and/or when the boiler water is discharged from the above pipes.SOLUTION: Inactive gas or inactive gas mixture is introduced such that gaseous oxygen in particular of atmospheric oxygen form present in each of flow volumes of pipes is substituted and/or the inactive gas or the inactive gas mixture is introduced so as to fill vacant volumes generated during discharging a boiler water of the steam from each of the flow volumes of the pipes, into a pipe wall area or the pipes of pipe sections through which the boiler water or the steam generated by introducing the inactive gas or the inactive gas mixture into the pipes flows during operation of the power generation station before filling with the boiler water or steam.