Dissolved oxygen causes pitting corrosion in feedwater lines and economizers. The roles of the deaerator, oxygen scavengers and amines.
Oxygen dissolved in feedwater causes pitting corrosion on hot steel surfaces. Such damage can locally perforate a tube wall.
Layers of protection
- Thermal deaeration: most of the oxygen is removed in the deaerator
- Oxygen scavenger: chemically binds the remaining traces
- Neutralizing amines: counter CO₂ (carbonic acid) in condensate and keep pH in range
- Filming amines: form a protective layer on the metal surface
What to monitor
- Dissolved oxygen in feedwater
- pH and conductivity
- Iron in condensate as a corrosion indicator
- Residual reagent in boiler water
The type of oxygen scavenger (for example sulfite or organic scavengers) is chosen based on boiler pressure, permissible dissolved solids and steam requirements.
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