The acid dew point is the temperature at which corrosive acids in the flue gas start to condense. If the acid dew point isn’t reached, e.g. during quenching, condensation of highly concentrated sulphuric acid can occur. As a result, special corrosion-resistant materials must be used or the relevant surfaces protected from contact with the condensates.

Example: Sulphuric acid: The acid dew point of sulphuric acid is 120 – 150°C and can sometimes reach up to 180°C.

The corrosive attack on many materials varies depending on the local acid concentration. For instance, carbon steel can be resistant to low concentrations of sulphuric acid, not resistant at all to medium concentrations of sulphuric acid and then be suitable again where concentrations of sulphuric acid are high.