Describe the effects of using shore fresh water as auxiliary boiler feedwater, the measures to reduce these effects, and the purpose and method of deaeration in the boiler feed water system?
Short answer
| Effect | Cause | Measure |
|---|---|---|
| Oxygen corrosion | Dissolved O₂ in shore fresh water | Deaerator, oxygen scavenger (Na₂SO₃/hydrazine) |
| Acidic corrosion | Low pH | Alkalinity control (NaOH), maintain pH 10–11 |
| Chloride corrosion | Municipal chlorine | Activated carbon filter |
| Scale | Residual hardness/silica | Internal treatment, blowdown |
| Carry-over | High total dissolved solids | Blowdown, control total dissolved solids |
- Primary effect: oxygen corrosion and pitting from dissolved O₂ in shore fresh water
- Secondary effects: acidic corrosion if pH low, chloride attack if chlorinated, scale from residual hardness or silica, carry-over if total dissolved solids high
- Key measure: deaeration (heating + spray into steam) + oxygen scavenger dosing
- Deaerator purpose: remove dissolved O₂ and CO₂ to prevent corrosion
- Deaeration method: heat feedwater to saturation temperature at deaerator pressure, spray into steam atmosphere, vent gases
- Control point: feedwater temperature above 90°C reduces O₂ solubility fourfold vs 50°C
- Tests: dissolved oxygen, pH, hardness, chloride, alkalinity
- Records: engine room logbook for tests, dosing, blowdown
- IMO requirement: means to supervise and control feedwater quality and preclude contaminants (A.1023(26) ch-4 §4.4.4; 2009 MODU Code cha-4 §4.4.4)
- India: Merchant Shipping Act 2025 applies; DGMA regulations govern boiler operation
Full answer
The full answer explains each point step by step, with the regulations and figures behind it and the discussion from other candidates. It is in the MEO Class IV section of the Marine One forum, open to members enrolled for the MEO Class IV exam.