USCG Exam PracticeBoiler and steam propulsion fundamentals
Scale formation on the water side of boiler tubes is primarily caused by which condition?
- A. Dissolved oxygen attacking the tube metal in an acidic environment
- ✓ Dissolved hardness salts such as calcium and magnesium coming out of solution as water boilsCorrect
- C. Seawater contamination raising chloride levels in the boiler water
- D. Insufficient blowdown allowing sludge to accumulate in the steam drum
Why B is correct
Scale is a hard mineral deposit that forms when dissolved hardness salts (calcium and magnesium) 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 drives corrosion; chloride rise signals seawater contamination; sludge accumulates in the water drum, not the steam drum. (NAVEDTRA 14104 §4-5)
Cited:NAVEDTRA 14104 §4-5