USCG Exam PracticeBoiler and steam propulsion fundamentals
Scale formation on the water side of boiler tubes is primarily caused by which of the following?
- A. Dissolved oxygen and carbon dioxide attacking the tube metal
- ✓ Dissolved hardness salts (calcium and magnesium) coming out of solution as water boilsCorrect
- C. Seawater contamination raising the chloride concentration
- D. Acidic boiler water maintained below the correct alkalinity range
Why B is correct
Scale is a hard mineral deposit formed when dissolved hardness salts precipitate out of solution during boiling. Even a thin scale layer insulates the tube from the water, causing the tube metal to overheat, lose strength, and potentially rupture. Dissolved oxygen and acidic water cause corrosion, not scale.
Cited:NAVEDTRA 14104 §4-5