Abstract: A method of preventing corrosion in boiler plant equipment when cooling flue gases originating from a combustion plant, such as flue gases containing sulphur oxide or organic acids, to a temperature beneath which sulfuric acid condenses (sulfuric acid dew point temperature) and a further temperature defined as an upper permitted wall-temperature of the stainless steel. The upper permitted wall temperature is with respect to the stainless steel material from which the walls are made and the prevailing partial pressure of water vapor present in the gases. This limiting temperature is specific to each stainless steel. The heat exchange is by means of a coolant, suitably water, located on the other, i.e.