Uncommon in operating boilers but may be found in idle boilers.Entire boiler susceptible , but most common in the superheater tubes (reheater tubes especially where water accumulates in bends and sags ). In an operating boiler firstly the economizer and feed heater are effected. In the event of severe contamination of oxygen areas such as the steam drum water line and the steam separation equipment. In all cases considerable damage can occur even if the period of oxygen contamination is short. Bare steel coming into contact with oxygenated water will tend to form magnetite with a sound chemical water treatment program. However, in areas where water may accumulate then any trace oxygen is dissolved into the water and corrosion by oxygen absorption occurs.
De-aerating feedwater heaters are provided to remove oxygen from feedwater to prevent corrosion. Oxygen scavengers such as hydrazine or sodium sulphite are used to remove the trace amounts of oxygen not removed by the de-aerator. Hydrazine is highly reactive with oxygen. Feedwater treatment with hydrazine prevents oxygen from corroding both the feedwater system and the boiler. Sodium sulphite may be added to boiler water to prevent oxygen corrosion.