Marine & Power-Plant Auxiliary Boiler, Exhaust-Gas Economiser Soot Fire & Water Treatment Guide

Auxiliary Boiler & Exhaust-Gas Economiser Fault, Safety Lock-Out & Diagnostic Matrix

1. SOLAS II-1/32 Boiler Safety Basics, Safety Valves & Gauge-Glass Blow-Through

Operating and fault-finding marine auxiliary steam boilers and power-plant waste-heat recovery boilers is core engineer officer competence under the STCW Code (Tables A-III/1 and A-III/2), while set pressures, water-level trip heights and blowdown intervals come from the boiler maker's instruction manual and the class society. At the statutory level, SOLAS Chapter II-1 Regulation 32 requires every steam boiler and unfired steam generator to have at least two safety valves of adequate capacity (the Administration may permit a single valve for some boilers, having regard to output or other features), and every boiler essential for the safety of the ship and designed to hold water at a set level to have at least two means of showing that level, at least one of them a direct-reading gauge glass. Pressure gauges, feed check valves, scum and blowdown valves follow the class rules and the maker's design.

Oil-fired boilers intended to run without manual supervision must also have safety arrangements that shut off the fuel and give an alarm on low water level, air supply failure or flame failure, so the burner goes out before tubes or the furnace crown are uncovered. Watchkeeping engineers must never take an unmoving meniscus in a dirty gauge glass at face value: a choked cock can show a false level while the drum runs dry. Wearing a face shield and gloves and standing to one side, engineers prove the true drum level by shutting the steam and water cocks, opening the drain cock to confirm it discharges freely, briefly opening and closing the steam cock to prove the steam passage, briefly opening and closing the water cock to prove the water passage, closing the drain cock, and reopening the water and steam cocks so the level returns briskly to its working mark. If it rises slowly or not at all, a passage is blocked.

If water disappears from the gauge glass and blowing through does not show the true level, shut off fuel to the burner immediately and isolate the firing circuit, and do not add feedwater until you know whether the level is high or low. If the boiler is short of water and the heating surfaces are overheated, cold feed can cause severe damage, tube rupture or an explosion. Let the boiler cool, find the cause (feed pump, level control or a leak), and inspect the tubes and furnace before refilling.

• Blow through the direct-reading gauge glasses at the interval in the maker's manual and the SMS, and whenever the level looks doubtful, wearing a face shield and gloves and standing to one side.
• Test the low-water alarm and the low-water fuel cut-out at the interval and by the method in the boiler maker's manual and the class rules, recording every test in the PMS.
• Check that the safety valve easing gear works freely from its operating position, and never gag or tamper with a safety valve; settings are made and sealed with the surveyor.
• If the true water level is lost, shut off fuel immediately, do not add feedwater until you know whether the level is high or low, inform the Chief Engineer, and let the boiler cool before inspecting or refilling.
• Keep main steam stop valves, feed check valves, scum valves and shipside blowdown valves free from spindle seizure, and check the blowdown valve's interlock or key arrangement where one is fitted.

2. Forced-Draught Pre-Purge, Fail-Safe Burner Trips & Fuel Changeover Control

A furnace explosion in an oil-fired boiler occurs when unburnt fuel mist or vapour collects in a hot furnace and ignites on the next ignition attempt. To prevent it, the burner management system runs a fan pre-purge before every ignition attempt, sweeping fresh air through the furnace and uptake to clear residual hydrocarbons before the igniter and fuel valves are allowed to open. For periodically unattended machinery spaces, SOLAS Chapter II-1 Regulation 52 requires a safety system that automatically shuts down that part of the plant and gives an alarm when a serious malfunction presents an immediate danger; flame failure, low water level, high steam pressure and combustion-air fan failure trips are set up by the maker and class to fail to a safe, fuel-off state.

Fuel quality and changeovers bring a second set of firing hazards. Under SOLAS Chapter II-2 Regulation 4.2.1, oil fuel generally must not have a flashpoint below 60 °C, and under Regulation II-2/4.2.2.6 surfaces above 220 °C that fuel could reach after a system failure must be properly insulated; spray shields on fuel pipe joints near hot surfaces are good practice. When an auxiliary boiler is switched between residual fuel and low-sulphur distillate for Emission Control Area compliance, viscosity and temperature change sharply: overheated distillate can vaporise in the burner and cause flame pulsation or flame-out, while under-heated residual fuel atomises poorly and leaves unburnt carbon on the refractory and downstream.

Before dismantling any burner gun, atomiser tip, flame eye or fuel block-and-bleed solenoid assembly, engineers must stop the burner, switch the local panel to locked-off isolation, close and tag manual fuel supply and return valves, and relieve trapped pressure and thermal energy in accordance with the maker's manual. Bypassing a flame-failure relay, jamming an air damper switch, or repeatedly pressing reset after consecutive ignition lock-outs floods the furnace floor with unburnt oil and sets the stage for a severe furnace explosion.

• Never press the burner reset button repeatedly after consecutive ignition failures: lock out fuel supply, inspect the furnace floor for unburnt oil, and ventilate thoroughly before fault-finding.
• Verify that forced-draught pre-purge timers, combustion air differential-pressure switches, and UV/IR flame scanners operate strictly as specified in the burner maker's manual.
• During residual-to-distillate fuel changeovers, switch off trace heating as required by the fuel system procedure so low-viscosity distillate does not gasify in the burner supply pump or atomiser.
• Inspect fuel flexible hoses, burner swing-frame interlocks, insulation on hot surfaces above 220 °C (SOLAS II-2/4.2.2.6) and spray shields on nearby fuel pipe joints during engine-room safety rounds.
• Clean rotary-cup, pressure-jet or steam-assisted atomiser tips with approved solvents and soft tools rather than steel wire so orifice geometry and spray-cone angles stay intact.

3. Exhaust-Gas Economiser Soot Fires: Low-Load Prevention & Emergency Response

Exhaust-gas economisers and waste-heat recovery boilers extract heat from main engine or gas-generator exhaust across closely pitched finned tube banks. During prolonged slow steaming, harbour manoeuvring, misfiring cylinder operation, or sudden dual-fuel gas-to-diesel transitions, exhaust temperatures drop while unburnt soot, cylinder oil mist and asphaltene residues condense onto the cooler finned tubes. Over time, rising gas-side differential pressure across the tube bank signals progressive choking, and once local exhaust temperatures rise again at sea speed or an incandescent spark enters the uptake, the soot layer can ignite.

Routine prevention centres on clean main engine combustion, tracking gas-side differential pressure (manometer or transmitter drop) and exhaust inlet versus outlet temperatures each watch, operating steam or compressed-air sootblowers at the frequency prescribed by the economiser maker, and carrying out scheduled water washing during port stays with uptake drains verified open so wash effluent cannot run back into the turbocharger or engine manifold. Where turbocharger dry or wet cleaning is carried out upstream, engineers coordinate soot-blowing sequences so dislodged deposits do not bridge finned economiser passages.

If a sudden rise in economiser outlet gas temperature, sparks from the funnel, a burning-paint smell or casing discolouration points to a soot fire, act early: a very hot soot fire can develop into a hydrogen or iron fire that is far harder to control. Alert the bridge and the Chief Engineer, slow or stop the main engine as navigation allows to cut off hot exhaust gas, keep every economiser inspection door closed so fresh air cannot feed the fire, do not use air sootblowers, follow the boiler maker's emergency instruction on circulating-pump operation and on using water through the economiser once the engine is stopped, and boundary-cool the surrounding uptake until temperatures return to normal.

• Log exhaust-gas economiser inlet temperature, outlet temperature and gas-side differential pressure each watch to spot soot bridging before gas passages choke.
• Operate sootblowers at the maker's interval at normal sea load, draining steam lines first so wet slugs do not erode the finned tubes.
• During port water-washing of economiser tube banks, verify drain lines are clear and collect acidic soot-wash effluent properly rather than letting water enter the turbocharger turbine casing.
• On any suspected economiser soot fire, inform the bridge at once, reduce or stop main engine exhaust flow safely, keep the casing inspection doors shut, do not use air sootblowers, follow the maker's emergency instruction, and boundary-cool the uptake.
• After any soot fire has cooled completely, isolate and lock out steam and water valves, ventilate the uptake, and pressure-test all economiser headers and return bends for pinholes before returning to service.

4. Boiler Water Treatment, IACS UR Z18 Surveys & MSC.581(110) Drum Entry

Untreated or contaminated feedwater damages boilers from the water side: hardness salts form insulating scale on hot tubes, causing overheating, while dissolved oxygen and carbon dioxide pit the drums and condensate lines, and a wrong alkalinity balance attacks protective films. Engineers draw a cooled boiler water sample through a sample cooler at the interval set by the maker, chemical supplier and SMS, test pH/alkalinity, phosphate, chlorides, oxygen scavenger reserve and conductivity, and dose chemicals and blow down to stay within the maker's and chemical supplier's limits.

Feedwater purity starts upstream in the cascade/observation tank and deaerator. Fuel oil or cargo heating coils return through an illuminated observation tank fitted with oil-in-water detection: even a slight film of oil entering the boiler coats generating tubes with a severe thermal barrier that causes rapid tube failure, requiring immediate coil isolation and chemical boil-out if contamination occurs. Equally, a sudden jump in feed or boiler water chlorides points to seawater leakage at the condenser, dump cooler or fresh-water generator distillate line, demanding prompt leak isolation and blowdown recovery.

Under IACS Unified Requirement Z18 (Survey of Machinery), boilers are examined internally twice in each 5-year special survey period, with the maximum interval set by the class rules, and externally at each annual survey, when the class society's rules decide which safety valves, gauges and boiler safety devices are seen working. Preparing a steam drum, water drum or furnace for internal inspection is high-hazard work: shut, padlock and tag the main steam stop valve, auxiliary steam valves, feed check valves, scum valve and shipside blowdown valve (including any links to a boiler still in service), vent the boiler to zero pressure, cool and drain it, and open the manhole doors carefully with the vents open, watching for steam and hot water. Every drum or furnace entry follows IMO Resolution MSC.581(110): a permit valid for no more than 8 hours and void if the space is left unattended, ventilation, an atmosphere test before entry (oxygen 20.9% by volume, flammable vapour below 1% of the lower flammable limit and toxic gases below 50% of their occupational exposure limit), an attendant with rescue equipment ready at the entrance, and Emergency Escape Breathing Devices (EEBDs) kept for escape only, never used for entry.

• Draw boiler water samples through a working sample cooler at the interval set by the maker and SMS, and keep alkalinity, phosphate, oxygen scavenger, chloride and conductivity values within the maker's and chemical supplier's limits.
• Inspect the hotwell/cascade observation tank and oil-in-water alarm each watch so a leaking bunker or cargo tank heating coil is diverted before oil reaches the feed pumps.
• Track IACS UR Z18 boiler survey windows in the PMS: two internal examinations in each 5-year special survey period and an external examination at each annual survey, with the class rules setting the maximum interval and the items tested.
• Before opening any boiler manhole door, lock and tag all steam, feed, chemical-dosing and blowdown valves against back-flow from adjacent live plant and verify zero gauge pressure and open air vents.
• Make every steam drum, water drum or furnace entry under an enclosed-space permit following IMO Resolution MSC.581(110): no more than 8 hours, void if left unattended, oxygen 20.9%, flammable vapour below 1% LFL, toxic gases below 50% OEL, and never an EEBD for entry.

Frequently Asked Questions

Related Marvel Solutionz & SeaReady Resources

Regulatory & Technical Sources

• IMO SOLAS Chapter II-1 Regulation 32 (Steam boilers and boiler feed systems) and Regulation 52 (Safety systems, periodically unattended machinery spaces); SOLAS Chapter II-2 Regulation 4 (Fire prevention)
• IACS Unified Requirement Z18 (Survey of Machinery), boiler surveys, and your class society's rules
• IMO Resolution MSC.581(110), Revised Recommendations for Entering Enclosed Spaces Aboard Ships
• IMO STCW Convention and STCW Code Tables A-III/1 & A-III/2 (Engineer Officer Competence)