Sulfite Residual

Definition

The measurable excess of sodium sulfite maintained in boiler water, typically 20 to 60 ppm, that confirms enough scavenger is present to consume incoming oxygen.

Operators feed roughly 10 ppm sulfite per 1 ppm oxygen to keep this residual, which gives a safety margin above the stoichiometric 7.88 to 1. A residual that tests at zero, sometimes shown by an orange tint in the sample, means oxygen demand has overwhelmed the scavenger and corrosion is accelerating. The residual is a key field diagnostic for oxygen control.

Related concepts

Oxygen Scavenger · Sodium Sulfite · Dissolved Oxygen

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Part of The Blueprint of Water · 📏 measurement