Marine Boiler

 

1. What Is a Marine Boiler?

A marine boiler is a closed pressure vessel that produces steam by heating water. This steam is used for:

• Fuel oil heating
• Tank cleaning
• Freshwater generation (via evaporators)
• Heating cargo (on tankers)
• Auxiliary machinery (like turbine-driven pumps)
• Accommodation heating

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 2. Types of Marine Boilers

Type	Description	Common Use
Smoke Tube Boiler	Hot gases pass through tubes, water surrounds them	Used in smaller ships (ex: Scotch Marine Boiler)
Water Tube Boiler	Water flows inside tubes, heated externally by gas	High-pressure systems, used in large ships or steamships

 

Common Types:

• Composite Boiler – Has both exhaust gas and oil-fired heating
• Exhaust Gas Boiler (EGB) – Utilizes main engine exhaust heat
• Oil-Fired Boiler – Uses diesel or heavy fuel oil to generate heat

 

3. Main Components of Marine Boiler

Component	Function
Furnace	Combustion chamber where fuel burns
Burner	Atomizes fuel for efficient burning
Water Drum/Steam Drum	Holds water/steam, separates steam from water
Superheater	Increases steam temperature (dry steam)
Economizer	Pre-heats feedwater using exhaust gas
Safety Valve	Prevents overpressure in the boiler
Pressure Gauge	Shows internal pressure of boiler
Feed Check Valve	Controls feedwater flow into boiler
Blow Down Valve	Used to remove sludge and impurities

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 4. Working Principle of Marine Boiler

1.  Fuel burns in the furnace using air (supplied by FD fan or natural draft).

2.  Heat transfers to water in tubes or around tubes.

3.  Water heats and turns into steam.

4.  Steam rises and collects in the steam drum.

5.  Steam is used for shipboard services.

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 5. Boiler Mountings and Fittings (as per SOLAS/Class)

Mounting	Purpose
Safety Valve	Releases steam if pressure exceeds set limit
Water Level Gauge	Shows water level inside boiler
Pressure Gauge	Displays boiler pressure
Blowdown Valve	Removes sludge and sediments
Main Steam Stop Valve	Controls steam flow to users
Feed Check Valve	Regulates feedwater entry

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6. Boiler Safety Systems

• Low Water Level Alarm & Trip
• High Steam Pressure Alarm
• Flame Failure Alarm (UV Sensor)
• Automatic Burner Control (ABC)
• Fuel Oil Shut-Off Valves
• Emergency Shutdown Button

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 7. Boiler Maintenance Tasks

Frequency	Task
Daily	Check water level, steam pressure, burner operation
Weekly	Blowdown, check safety valve and burner tips
Monthly	Test alarms and trips
Yearly	Internal inspection, descaling, pressure testing

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 8. Boiler Code Requirements

• Must comply with SOLAS Chapter II-1
• Pressure vessels follow Class society rules (e.g., Lloyd’s, DNV)
• Regular survey and certification by Class
• Periodic hydrostatic pressure testing

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 9. Boiler Hazards

• Boiler explosion (due to overpressure or low water)
• Furnace blowback (due to poor purging)
• Burns from hot steam or water
• Corrosion and scaling from untreated water

 

Q1: What are boiler mountings?

✅ Answer: Boiler mountings are essential safety and control fittings such as safety valve, pressure gauge, water level gauge, blowdown valve, steam stop valve, and feed check valve.

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🌡️ Q2: What actions if low water level alarm activates?

✅ Answer:

• Raise the alarm
• Stop the burner immediately
• Do not add water suddenly (risk of thermal shock)
• Check both water gauges
• Inform Chief Engineer
• Investigate cause (e.g., feed pump failure)
• Only restart after confirming water level and safety

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⚠️ Q3: What is a flame failure alarm?

✅ Answer: It's an alarm triggered when the flame goes out unexpectedly. A UV sensor detects no flame and shuts off fuel to prevent unburnt oil buildup, avoiding explosion risk.

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🧪 Q4: What is boiler blowdown?

✅ Answer: It's the process of draining water from the boiler to remove impurities, sludge, and dissolved solids that can cause scaling or corrosion.

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🛑 Q5: What safety devices are fitted on a marine boiler?

✅ Answer:

• Safety valve
• Pressure gauge
• Water level gauge
• Low water level alarm & trip
• Flame failure trip
• Emergency stop switch
• Feed check valve

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🛠️ 3. Boiler Troubleshooting Checklist

🚨 Problem	🔍 Likely Cause	✅ Action
No Steam Pressure	Burner not firing, feed pump failure	Check burner, fuel supply, feedwater level
Low Water Level	Leak, faulty feed pump	Stop burner, check feed pump, refill water
Boiler Overpressure	Safety valve stuck, control failure	Stop burner, open vent, check pressure control
Flame Failure Alarm	No fuel, air interlock open, ignition failure	Check oil supply, check UV sensor, reset burner
Excessive Soot or Smoke	Poor combustion, dirty burner	Clean burner, check atomization and air/fuel ratio
Boiler Water Foaming	High TDS, oil contamination	Blowdown, add chemical, renew water
Boiler Tripping Repeatedly	High pressure or temp, control failure	Investigate trips, recalibrate control systems

 

 

SOLAS Regulations for Marine Boilers

Marine boilers are pressure vessels and heat-generating equipment governed by SOLAS Chapter II-1 and Chapter II-2, along with Class rules (like DNV, ABS, LR) and the Boiler and Pressure Vessel Code (ASME).

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 Applicable SOLAS Chapters

SOLAS Chapter	Relevance
Chapter II-1 – Construction	Design, strength, and safety of boiler as machinery
Chapter II-2 – Fire Protection	Fire safety for fuel-burning equipment (like boilers)
Chapter III – Life-saving	Covers safety near accommodation if boiler is close
Chapter IX – ISM Code	Ensures SMS includes boiler safety procedures

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Why Test Boiler Water?

To:

• Prevent scale formation on heating surfaces
• Avoid corrosion of boiler tubes, drums, and valves
• Maintain boiler efficiency and safety
• Prevent foaming, priming, and carryover

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🧪 Common Boiler Water Tests

Test Name	Purpose	Acceptable Range
1. pH Test	Prevent corrosion (acid/base level)	9.5 – 11.0
2. Chloride Test	Detect salt water contamination	< 50 ppm
3. Phosphate Test	Prevent scale formation (buffer)	20 – 40 ppm
4. Alkalinity (P & M)	Controls corrosion/scale	P: 100-200 ppm (as CaCO₃)
5. Hardness Test	Detect calcium/magnesium (scale)	0 ppm (soft water only)
6. Dissolved Oxygen	Prevent corrosion	< 0.005 ppm (use oxygen scavenger)
7. Conductivity Test	Detect contamination/salts	< 2000 µS/cm
8. Total Dissolved Solids (TDS)	Indicates overall water purity	As per boiler design

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🧑‍🔬 How to Perform Boiler Water Testing (Step-by-step):

1.  Take a clean water sample from the boiler water test cock.

2.  Cool it down to room temperature.

3.  Use the Boiler Water Test Kit (e.g., Spectrapak, Nalfleet).

4.  Follow kit-specific drop test or tablet method for each parameter.

5.  Record all readings and compare with manufacturer’s limits.

6.  Add chemical treatment if required (phosphate, oxygen scavenger, alkali, etc.)

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🧴 Common Chemicals Used

Chemical	Purpose
Sodium Phosphate	Scale prevention
Hydrazine / DEHA	Oxygen scavenger
Sodium Hydroxide	pH and alkalinity control
Antifoam agent	Prevent foaming

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⚠️ Dangers of Improper Boiler Water Treatment

• 🔥 Overheating of tubes (due to scale)
• 🧨 Tube rupture or explosion
• 🔩 Corrosion of water drum/steam lines
• 🌊 Priming and carryover (moisture in steam)
• 📉 Loss of boiler efficiency

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🧠 Oral Q&A Samples:

Q1: Why is pH kept between 9.5–11 in boiler water?

To avoid acidic corrosion and to promote passive oxide layer on metal surfaces.

Q2: What happens if chlorides are high?

Indicates seawater ingress → leads to corrosion and foaming.

Q3: What is the use of phosphate in boiler water?

Reacts with calcium to form non-adherent sludge, preventing scale.

Q4: What is the effect of high TDS?

Causes foaming, priming, and wet steam.

Q5: What chemical is used to remove oxygen from boiler water?

Hydrazine or DEHA (oxygen scavengers).

 

 

 Key SOLAS Requirements for Marine Boilers

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1. Boiler Construction and Testing

SOLAS Chapter II-1, Regulation 26 & 30

• Boilers must be:
• Properly constructed as per recognized standards
• Tested hydrostatically to 1.5 times design pressure
• Designed with proper safety margins
• Material must be resistant to heat, corrosion, and pressure

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 2. Boiler Mountings & Fittings (Mandatory)

As per SOLAS and Class Rules:

• At least one safety valve (two for high-capacity boilers)
• Water level indicators (minimum 2 for large boilers)
• Pressure gauge
• Blowdown valve
• Feed check valve
• Steam stop valve
• Low water level alarm and trip
• Emergency shutoff system

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3. Automatic Burner Controls

SOLAS II-1 Reg. 30

• Oil-fired boilers must have:
• Automatic flame detection system
• Flame failure safety shutdown
• Purge cycle before ignition
• High steam pressure trip

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 4. Fuel Oil System Safety (for Boiler Firing)

SOLAS Chapter II-2, Regulation 4.2.2

• Fuel oil must not be sprayed onto hot surfaces
• Heated fuel oil pipes must be properly shielded
• Quick closing valves required on fuel lines
• Emergency shutoff from outside boiler room

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 5. Fire Detection and Extinguishing

SOLAS Chapter II-2, Regulation 7, 10, 11

• Boiler room must be equipped with:
• Fixed fire detection system
• Fixed fire suppression system (CO₂, foam, or water mist)
• Portable extinguishers nearby
• Proper ventilation and fire insulation

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 6. Boiler Operation Alarms & Trips

• Low water level alarm and shutdown
• High steam pressure alarm
• Flame failure alarm
• High furnace temperature (if monitored)
• Forced draft fan interlock with burner

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 7. Draining and Maintenance

• SOLAS mandates safe blowdown operation
• Drains must be arranged to prevent harm or fire
• Routine maintenance and logging required as part of ISM Code

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 Certificates and Survey

• Boilers must be classed and certified
• Regular survey and inspection:
• Annual safety check
• 5-year internal inspection
• Hydrostatic pressure test
• Records must be kept for:
• Maintenance
• Safety valve settings and tests
• Alarms and shutdowns

Q: What SOLAS rules apply to marine boilers?
✅ Answer: SOLAS Chapter II-1 ensures boilers are built, tested, and fitted with all mountings. Chapter II-2 requires fire detection, flame failure trips, and emergency fuel shutoff systems. The boiler must be maintained and surveyed under class and ISM Code.