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Module 19 • Crib Sheet

Boiler Systems & Water Treatment Infographic

High-detail MCA oral revision sheet covering boiler safeties, mountings, steam raising, burner management, water chemistry, corrosion, blowdown, inspection checks, EGB faults and emergency responses.

Critical risk

Low water + continued firing
Overheated tubes/shell can fail catastrophically. Stop firing first.

Chemistry control

Prevent scale, corrosion and carryover
Control pH, alkalinity, TDS/conductivity, phosphate, chlorides and oxygen scavenger reserve.

Inspection focus

Water side + gas side + safeties
Scale, pitting, sludge, oil, refractory, burner throat, tube defects, flame impingement and safety-valve condition.

How to use this crib sheet

This page is a compact boiler systems and water-treatment crib sheet designed for quick recall before mocks, tuition or oral exam preparation.

  • Learn the first-action responses for low water, flame failure, high salinity, oil contamination, steam leaks and EGB fire.
  • Separate boiler safeties, mountings, burner management, water-treatment control and inspection evidence.
  • Use the chemistry table to diagnose chlorides, TDS, pH, alkalinity, phosphate and oxygen scavenger problems.
  • Explain boiler furnace purging clearly: what it means, why it is done, what permissives prove, and why re-purge is required after flame failure.
  • Define caustic embrittlement and link it to high alkalinity, local caustic concentration, stressed crevices and cracking risk.
  • Use the inspection matrix to structure a Chief Engineer-level boiler survey answer.
Start crib sheet

Crib Sheet Contents

01 Golden Rulesfirst actions 02 Steam Cyclesystem overview 03 Safetiesmountings & trips 04 Operationpurge & steam raising 05 Chemistrytest interpretation 06 Scale/Corrosionmechanisms 07 Blowdownsampling & TDS 08 Inspectionsurvey checks 09 EGB Faultssoot & iron fire 10 Oral Scenariossay this first 11 Lay-upshutdown chemistry 12 Memory Wallone-line facts
0 sections marked complete

01 • Golden Safety Rules

Boiler Oral Exam First Actions

Low-low waterStop firing. Do not feed cold water if level is lost. Verify locally and cool safely.
Flame failureFuel shuts. Find cause. Manual reset only after full purge and safe light-off checks.
High chloridesTreat as sea-water ingress. Find source, isolate, dump contaminated water and rebuild chemistry.
Oil in hotwellDivert dirty returns, protect boiler, isolate leaking heater/coil, do not feed oil to boiler.
Steam leakProtect people, inform Bridge/Chief, stop firing/reduce EGB source, isolate if safe.
EGB fireKeep circulation if possible, reduce/stop engine, seal air paths and boundary cool if escalated.

Exam phrase

“On a boiler question I will always protect personnel, stop heat input if unsafe, confirm the condition locally, avoid thermal shock, then investigate the root cause before restart.”

02 • System Overview

Steam, Feed and Condensate Flow

Marine Boiler Water / Steam Circuit Hotwell /Feed Tank Feed Pump +Feed Check Boilersteam drum / shellwater space + furnace Bottom / Surface Blowdown Steam Consumers Traps / Drains

What the boiler is doing

A boiler is a pressure vessel/heat exchanger converting treated water into steam. On diesel ships, steam is mainly used for fuel heating, domestic/hotel heating, tank cleaning/heating, cargo duties and auxiliary services.

Composite / Exhaust Gas Boiler

A composite boiler combines an oil-fired section with an exhaust-gas section. The EGB must maintain circulation; loss of circulation can quickly overheat tubes and escalate soot/iron fire risk.

Oral shortcut: “Feedwater quality controls the boiler’s life. Poor feedwater creates scale and corrosion, while poor operation creates carryover, water hammer and safety-device trips.”

03 • Mountings and Safeties

Mechanical Protection vs Burner Management Trips

MECH

Safety valves

Independent overpressure protection. Normally at least two on a steam boiler. Easing gear allows manual lifting from a safe position.

LEVEL

Gauge glasses / level indication

Two independent means of water-level indication; blow through steam and water connections to prove clear passages.

FEED

Feed check / stop valves

Permit feedwater entry and prevent steam/water backflow into the feed system or idle boiler.

BLOW

Bottom blowdown and scum/surface valve

Bottom blowdown removes sludge; surface/scum blowdown removes floating matter and dissolved-solids concentration near the water surface.

Electrical / BMS tripWhy it tripsRestart condition
Low-low waterProtects tubes/shell from overheating and collapse.Do not restart until level is proven, cause found and boiler is safe.
Flame failurePrevents fuel continuing into a dark furnace.Manual reset and full purge before re-ignition.
Combustion air failurePrevents rich mixture, smoke, flame instability and blowback.Fan/damper/air pressure proven.
High steam pressureStops firing before safety valve lift or overpressure.Pressure reduced, control fault cleared.
Burner door / atomiser faultStops unsafe burner operation or poor atomisation.Door proved shut; atomiser/fuel system healthy.

Gauge glass blowdown sequence

Normal condition: steam and water cocks open, drain shut. Open drain, shut/open steam and water cocks in turn to prove both connections clear, then shut drain and restore water then steam carefully. If water cannot be proven, stop firing and investigate.

04 • Burner Management and Steam Raising

Purging, Ignition and Warm Through

What boiler purging means

Purging is the forced ventilation of the furnace and gas passes before ignition. The forced-draught fan moves a large volume of fresh air through the furnace, uptake and boiler gas path to remove any unburnt fuel mist, vapour or combustible gas left from a failed start, leakage or previous flame failure.

Exam line: “Purge first, ignition second. The purpose is explosion prevention by proving the furnace is clear of a flammable mixture before fuel is admitted.”

Why it is critical

If oil vapour or unburnt fuel remains in the furnace, the igniter can ignite the whole mixture at once, causing blowback, furnace explosion, burner door failure, refractory damage and serious injury.

  • Never bypass a purge timer or air-flow proof.
  • Never repeatedly reset flame failure without investigating.
  • Fuel valves must remain shut until purge and ignition permissives are satisfied.
1. Demand / start commandBoiler pressure falls or operator selects start. Control system checks water level, pressure, fuel temperature, fan availability, burner position and interlocks.
2. Fuel shut / air provenMain fuel valves remain shut. Forced-draught fan starts and the air-flow switch or pressure switch proves sufficient combustion air movement.
3. Damper to purgeAir damper drives to purge/high-air position so the furnace and uptake receive the required air volume for the required time.
4. Timed purgePurge timer runs only while fan and air-flow permissives remain healthy. Any failed permissive resets the purge and prevents ignition.
5. Ignition trialDamper moves to light-off position. Igniter energises. Pilot/main fuel valve opens only for the permitted trial-for-ignition period.
6. Flame provenFlame scanner proves stable flame. If flame is not proven, fuel shuts, alarm/trip activates and a new purge is required before another attempt.
7. Low-fire warm throughBurner remains at low fire while boiler and steam lines warm gradually. Keep drains open and avoid water hammer.
8. Modulation / loadBurner modulates with steam pressure demand. Monitor flame shape, smoke, fuel viscosity/temperature, water level and boiler pressure.
9. Shutdown / post-purgeFuel shuts first. Fan may continue for a post-purge to clear remaining vapours and cool the furnace as per burner sequence.
Purge permissiveWhat it provesIf it fails
FD fan runningVentilation source is available.No purge, no ignition. Check motor, starter, overloads and supply.
Air-flow / air-pressure switchActual air movement through the furnace is adequate.Fuel valves remain shut. Check damper, fan belt/coupling, blocked intake or faulty switch.
Damper purge positionHigh-air path is open enough to sweep furnace volume.Purge timer should not complete. Check actuator/linkage/limit switch.
Timed purge completeFurnace has been ventilated for the required time/volume.Ignition permissive is withheld until completed continuously.
Fuel valves shut before purgeNo additional fuel is admitted during ventilation.Investigate valve leakage before restart.
Flame scanner dark before ignitionNo false flame signal exists before light-off.Lockout/fault finding before ignition trial.

Pre-purge vs post-purge

Pre-purge is carried out before ignition to sweep the furnace and gas passes clear of unburnt fuel vapour. Post-purge is fan ventilation after fuel shut-off to clear residual vapours and reduce hot-spot ignition risk.

What controls the purge time?

The exact time is maker/BMS specific. The safe oral answer is: the purge must move the required volume of air through the furnace for the programmed time, with fan running, damper position and air-flow proven continuously.

After flame failure

Fuel must shut immediately, the fault must be investigated, and a fresh full purge is required before any further ignition attempt. Repeated reset without purge can fill the furnace with an explosive mixture.

Chief Engineer wording: “I would not treat purge as a time delay only. I would prove air movement, damper travel, no false flame, shut fuel valves and correct BMS sequence before allowing ignition.”

Correct steam-raising behaviour

  • Fill to correct level with treated water and verify gauge glasses locally.
  • Open air vent when cold and close when steam issues steadily.
  • Warm through at low fire to limit thermal stress.
  • Open line drains and crack steam stop valves slowly.
  • Watch water-level swell and shrink as pressure/load changes.

Common oral traps

  • Calling purge “cleaning soot” — it is primarily to remove explosive vapours.
  • Restarting immediately after flame failure without a fresh purge.
  • Opening steam stops quickly onto cold lines, causing water hammer.
  • Ignoring poor atomisation, unstable flame, black smoke or delayed ignition.
  • Failing to mention low-low water as a hard burner trip.

05 • Water Chemistry Crib

What Each Test Tells You

pHtypically alkaline

Keep boiler water alkaline to reduce acidic corrosion and support magnetite. Too high can increase foaming/carryover and caustic attack risk.

P-AlkalinityOH + half carbonate

Phenolphthalein alkalinity indicates hydroxide and part carbonate alkalinity. Helps control phosphate/alkalinity programme.

T-Alkalinitytotal reserve

Total acid-neutralising reserve. High values can point to over-treatment and may require controlled blowdown.

Phosphatescale control

Combines with calcium/magnesium hardness to form soft, non-adherent sludge removable by bottom blowdown.

Oxygen scavengerpitting control

Hydrazine, sodium sulphite, DEHA or similar products remove dissolved oxygen and prevent localised oxygen pitting.

Chloridessalt ingress marker

High chlorides indicate sea-water contamination from condenser/FWG/heater leak or contaminated condensate/feed.

Conductivity / TDSsolids concentration

High dissolved solids increase foaming, carryover and deposit risk. Controlled by surface blowdown/skimmer or automatic conductivity control.

Hardnessscale source

Calcium/magnesium salts precipitate under heat and concentration. Pretreatment and phosphate programme prevent hard scale.

Condensate pHreturn-line corrosion

CO2 forms carbonic acid in condensate. Neutralising or filming amines protect condensate pipework, traps and returns.

Test resultLikely meaningRiskImmediate corrective thinking
High chloridesSea-water ingress / condenser or FWG leak / contaminated returns.Rapid corrosion, foaming, high TDS, unsafe steam quality.Find source, isolate contaminated return, dump/renew water, restore chemical reserve.
Low pHAcidic conditions or condensate CO2 issue.General corrosion and thinning.Check dosing, condensate pH, amines and source of contamination.
High alkalinityOverdosing or concentration by evaporation.Foaming, priming, carryover and caustic corrosion.Controlled blowdown, review dosing rate and load changes.
Low phosphateInsufficient reserve or high hardness demand.Hard scale on heating surfaces.Dose correctly, verify feed quality, bottom blowdown sludge.
Low scavengerOxygen not being chemically removed.Pitting corrosion.Check deaeration, dose reserve, sample quality and feed temperature.
High conductivity/TDSExcess dissolved solids / insufficient blowdown.Carryover, foaming, deposits.Surface blowdown, check auto conductivity control and contamination source.

06 • Scale and Corrosion

Why Chemistry Failures Destroy Boilers

Heating Surface Risk Fireside metal / tube plate / furnace wall Overheated metal when scale insulates waterside Hard scale / baked sludge / oil film Boiler water must receive heat Scale forces metal temperature and stack temperature upwards. 1 mm scale can move metal beyond safe range scale can push fireside metal temperature far above normal safe values.

Scale

Calcium carbonate, silicates, phosphates and iron oxides insulate heating surfaces. Metal temperature rises, efficiency falls and tube/shell failure risk increases.

Oxygen attack

Dissolved oxygen causes localised pitting. Cold makeup and poor deaeration/scavenger reserve accelerate damage.

Caustic embrittlement

Concentrated caustic alkalinity in stressed crevices can cause intergranular cracking/embrittlement, not just general corrosion.

Acid condensate

CO2 in steam forms carbonic acid when condensed, lowering condensate pH and thinning return pipework.

High-yield fact

Scale is dangerous because it thermally insulates the waterside. The metal cannot transfer heat into the water effectively, so the metal temperature and exhaust temperature rise. Even thin deposits can cause overheating, creep, efficiency loss and tube failure.

Caustic embrittlement - definition

Caustic embrittlement is a form of stress-corrosion cracking in boiler metal caused when caustic alkalinity concentrates in small stressed areas such as tube ends, seams, stays, rolled joints, cracks or crevices. The concentrated caustic attacks the protective film and promotes cracking, so the metal can fail even though the general shell plate may appear sound.

Why it happens

  • Excess alkalinity or free caustic in boiler water.
  • Local concentration by evaporation at hot surfaces or leakage paths.
  • High residual stress around seams, tube ends, riveted/rolled joints or crevices.
  • Deposits that trap concentrated chemicals against the metal.

Prevention and control

  • Maintain pH, phosphate and alkalinity within the vessel treatment supplier’s limits.
  • Avoid overdosing caustic and avoid uncontrolled concentration through poor blowdown.
  • Control TDS/conductivity and chlorides; investigate contamination early.
  • Keep watersides clean so chemicals cannot concentrate under deposits.
  • Inspect stressed joints, tube ends and crevices during surveys.

Oral exam distinction

Scale overheats metal by insulation. Oxygen pitting is localised corrosion from dissolved oxygen. Caustic embrittlement is cracking driven by concentrated alkali plus stress, usually at crevices or highly stressed areas.

07 • Blowdown and Sampling

Control Sludge, Floating Matter and Dissolved Solids

Bottom blowdown

Short, controlled discharge from the lowest part of the boiler to remove heavy sludge and precipitated solids. Excessive or poorly timed bottom blowdown wastes heat and can upset level.

Surface / scum blowdown

Removes floating matter and concentrated dissolved solids near the water surface. Used for TDS/conductivity control and reducing carryover risk.

Cycles of concentration

Ratio between boiler-water dissolved solids and feedwater dissolved solids. The value depends on feed quality, boiler pressure, treatment programme and blowdown control.

Steam space Boiler water Surface/scum Bottom blowdown sludge settles low

Sampling rules

  • Use a sample cooler and take samples at about 20-25°C to avoid flashing volatile components and burning personnel.
  • Use clean, labelled bottles; flush the bottle with the sample before collection.
  • Do not mix condensate and boiler-water bottles; cross contamination can ruin chloride/alkalinity interpretation.
  • Trend results daily under changing load, not only as isolated readings.
  • Link every sample result to an action: dose, blowdown, investigate ingress or adjust treatment.

08 • Inspection and Survey

What to Check on Water Side, Gas Side and Mountings

AreaLook forWhy it mattersOral answer action
Water sideHard scale, sludge, oxygen pitting, caustic cracking, oil film, magnetite condition.Controls heat transfer, corrosion and tube/shell integrity.Clean, photograph, record, test deposits if required, correct chemistry.
Gas / furnace sideRefractory cracks/spalling, burner throat damage, soot, flame impingement, blistered tubes, water leak traces.Shows combustion quality, overheating and structural risk.Clean fireside, repair refractory, investigate flame pattern and tube defects.
Safety valvesSeat/disc pitting or wire drawing, spindle straightness, guides, springs, drains clear.Valve must lift/reseat reliably and discharge dry steam safely.Strip/inspect with Class, set and seal after approved pressure test.
Gauge glassesClear passages, valves free, glass/mica/gaskets condition, guards fitted.False level is one of the highest boiler risks.Blow through safely and compare independent level indication.
Feed systemPump condition, feed checks, hotwell quality, deaeration, contamination returns.Poor feed quality causes oxygen attack, scaling and carryover.Prove pump/standby, feed temperature, chemical reserve and contamination isolation.
RecordsPMS, logbook, water tests, safety-valve certificates, NDT, LOTO/PTW, defect closure.Evidence supports safe operation, survey and management control.Update records before return to service.

Survey prep sequence

Review history, risk assess/PTW/LOTO, cool gradually, drain, vent, open, clean, stage/lighting, inspect water/gas sides, prepare safeties, arrange NDT and Class attendance.

Accumulation test

Firing test to prove safety valves can discharge all generated steam with main stop closed. Oral figure: pressure should not rise more than 10% above MAWP; verify maker/Class procedure.

Tube defect

Stop, isolate, cool, drain, inform Chief/Class. Repair only with approved materials/procedure/qualified welder/NDT, or plug only within maker/Class acceptance.

09 • Exhaust Gas Boiler and Composite Boiler

EGB Circulation, Soot Fire and Iron Fire Response

EGB water circulation loss

  • Inform Chief/Bridge immediately.
  • Try standby circulation pump and verify valves/power/suction.
  • If circulation cannot be restored, reduce/stop main engine to remove heat input.
  • Do not allow a dry EGB to remain in a hot exhaust stream.

Soot fire stages

  • Minor: rising outlet temperature, sparks, smoke/opacity - keep circulation and monitor.
  • Escalating: rapid pressure/temperature rise, visible flame, safety valve activity - stop/reduce engine, seal air, boundary cool.
  • Do not use soot blowers once fire is established and escalating.
Iron fire / hydrogen risk: At very high temperatures, water can dissociate into hydrogen and oxygen, creating explosion risk. In an extreme EGB iron fire, concentrate on removing heat input, sealing air where possible and boundary cooling as per ship procedure.

10 • Oral Scenario Matrix

Say This First, Then Expand

  • Low water: “Stop firing immediately. I would not add water if the level is lost because the furnace/tubes may be overheated; I would verify level locally and investigate feed or leakage.”
  • Gauge glass blocked: “Blow through both sides to prove steam and water passages. If water cannot be proven, treat it as unsafe and stop firing.”
  • High chlorides: “Assume sea-water ingress until proven otherwise. Find the source before relying on blowdown alone.”
  • Oil contamination: “Protect the boiler first by diverting contaminated returns and isolating the leaking consumer; oil inside the boiler causes local overheating.”
  • Priming/carryover: “Reduce load if necessary, check level, high TDS/alkalinity/oil, operate correct blowdown and protect steam consumers.”
  • Safety valve survey: “Inspect seat/disc/spindle/spring/guides/drain, then set lift/reseat pressures under approved Class procedure and seal.”
  • Raising steam from cold: “Vent air, fill with treated water, warm slowly at low fire and open drains to avoid thermal stress and water hammer.”
  • Boiler purge failure: “No purge means no ignition. I would prove FD fan, air-flow switch, damper purge position, fuel shut valves and no false flame signal before allowing another start.”
  • Caustic embrittlement: “It is cracking caused by concentrated caustic alkalinity at stressed crevices; prevent it by controlling alkalinity, phosphate, TDS/blowdown and keeping watersides clean.”
  • Steam leak: “Protect personnel, notify Bridge/Chief, stop firing or reduce heat source, isolate the affected branch if safe, and monitor hotwell/boiler levels.”

11 • Lay-up and Chemical Cleaning

Shutdown Chemistry and Oil/Scale Recovery

Short-term wet lay-up

For short shutdowns, exclude air and maintain elevated oxygen scavenger reserve and alkalinity. Maintain a suitable oxygen-scavenger reserve and alkaline pH in line with vessel treatment instructions.

Long-term lay-up

Either keep dry and exclude moisture, or fill completely to exclude air with corrosion-inhibitor treatment. Test reserve and pH periodically.

Oil contamination cleaning

Find and isolate the oil source first. Remove oily sludge mechanically where possible, then degrease/boil out before returning to normal chemistry.

Chief Engineer mindset: lay-up is corrosion prevention. The danger is oxygen plus moisture on idle metal surfaces; chemistry and exclusion of air must be deliberate, recorded and periodically checked.

12 • Memory Wall

High-Yield One-Line Facts

Two gauge glasses

Water level is the most critical boiler safety parameter, so independent cross-checking is essential.

Do not feed lost level

Cold feedwater onto overheated metal can cause thermal shock and catastrophic failure.

Pre-purge saves lives

It removes explosive vapour before ignition after shutdown or flame failure.

Phosphate makes sludge

Hardness is converted to soft sludge which must be removed by bottom blowdown.

Chlorides = ingress

High chlorides point to sea-water contamination; find the leak source.

TDS = carryover risk

High dissolved solids encourage foaming, priming and wet steam.

CO2 attacks condensate

Carbonic acid lowers pH and causes condensate-line thinning, especially at bends and threaded joints.

Oil insulates

Oil film on the water side causes local overheating, blistering and tube cracking.

Caustic embrittlement

Concentrated caustic plus stressed crevices can cause intergranular cracking.