Oxygen Scavengers

Dissolved oxygen is one of the most destructive contaminants in boiler feedwater. Even at concentrations measured in parts per billion, oxygen causes aggressive pitting corrosion in feedwater piping, economizers, and boiler tubes, damage that is irreversible, accumulates over time, and can result in sudden tube failures. Unlike scale, which reduces efficiency gradually, oxygen pitting attacks at discrete points and creates localized conditions that accelerate further corrosion beneath the pit.

Most boiler systems include a deaerator that uses steam to strip dissolved oxygen from feedwater through mechanical degassing. A properly operating deaerator can reduce oxygen from several parts per million down to 7 parts per billion or less. But mechanical deaeration alone is rarely sufficient, load swings, condensate returns, and makeup water additions can introduce oxygen spikes that bypass mechanical treatment. Chemical oxygen scavengers provide the final polish, reacting with residual dissolved oxygen before it reaches boiler surfaces.

The right scavenger depends on system pressure, condensate return percentage, and environmental considerations. Catalyzed sodium sulfite is widely used in low- to medium-pressure applications. DEHA offers additional metal passivation benefits and is preferred in high-pressure systems or where significant condensate return is present. Organic alternatives such as carbohydrazide, erythorbate, and ascorbate address specific toxicity or discharge requirements. All scavenger programs require monitoring through residual testing and dissolved oxygen measurement to confirm effective dosage without excess.

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