Marine Engineering Practice Exam

Which inhibitor type is used as an oxygen scavenger in boiler water treatment?

Sodium chloride. Sodium phosphate. Polymer-based anti-scaling agents. Oxygen scavengers such as sodium sulfite.

Correct Answer:

Oxygen scavengers such as sodium sulfite.

Explanation:

Removing dissolved oxygen from boiler feedwater is essential to prevent corrosion of steel components. An oxygen scavenger is a chemical that reacts with dissolved oxygen to remove it from the water. Sodium sulfite is a classic oxygen scavenger: it reacts with O2 to form sodium sulfate, 2 Na2SO3 + O2 → 2 Na2SO4, thereby reducing the amount of oxygen available to oxidize metal. The other substances do not remove oxygen themselves: sodium chloride is simply a salt that can promote corrosion; sodium phosphate mainly acts as a pH buffer and helps with phosphate-based corrosion control but does not scavenge oxygen; polymer-based anti-scaling agents prevent mineral deposition and do not remove dissolved oxygen.

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