Boiler Interview Questions

1. What is a boiler and what is its main function?

A boiler is a closed vessel that converts water into steam using heat energy from fuel combustion.

The main function is to generate steam at desired pressure and temperature for process or power generation.

Steam produced is used for heating, power, or mechanical work.

It operates under controlled conditions of pressure, temperature, and safety.

2. What are the different types of boilers?

Based on contents in tube:

Fire-tube boiler – hot gases flow through tubes surrounded by water.

Water-tube boiler – water flows through tubes heated externally by hot gases.

Based on firing method:

Pulverized fuel, Fluidized bed, Package boiler, Field erected

Based on pressure:

Low-pressure, High-pressure, and Supercritical boilers.

Based on fuel type:

Coal, Oil, Gas, Biomass, Waste heat recovery.

3. What is the difference between a fire-tube and a water-tube boiler?

Fire-tube Boiler:

Hot gases pass through tubes surrounded by water.

Operates at low pressure (up to 25 bar).

Lower efficiency, suitable for small capacities.

Water-tube Boiler:

Water flows inside tubes and hot gases outside.

Operates at high pressure (up to 150 bar or more).

Higher efficiency and faster steam generation.

Common in industrial and power plants.

4. What is the working principle of a boiler?

Based on the transfer of heat energy from fuel combustion to water.

Combustion → Heat → Water → Steam.

Heat from burning fuel is absorbed by boiler tubes containing water.

The water converts into steam under pressure, collected in a steam drum.

Principle: “Heat energy converts liquid water into vapor (steam) at constant pressure.”

5. What are the main components of a boiler?

Furnace / Combustion chamber – where fuel is burned.

Burner – mixes fuel and air for efficient combustion.

Water drum / Steam drum – stores and separates steam from water.

Economizer – preheats feedwater using flue gas heat.

Superheater – raises the temperature of generated steam.

Air preheater – heats combustion air using waste flue gas.

Safety valves, pressure gauges, feed pumps, blowdown valves – for safe and controlled operation.

6. What is the function of the economizer, superheater, and air preheater?

Economizer:

Recovers waste heat from flue gases to preheat feedwater.

Improves efficiency and reduces fuel consumption.

Superheater:

Converts saturated steam to superheated steam by removing moisture.

Increases efficiency and prevents turbine blade erosion.

Air Preheater:

Heats incoming air using flue gas heat.

Enhances combustion efficiency and overall boiler performance.

7. What is meant by boiler efficiency? How is it calculated?

Boiler efficiency is the ratio of useful heat output to total heat input from fuel.

Indicates how effectively the boiler converts fuel energy into steam energy.

Formula:

Boiler Efficiency (%) = (Heat Output / Heat Input) × 100

or

Boiler Efficiency (%) = [(Steam Output × (Enthalpy of Steam – Enthalpy of Feedwater)) / (Fuel × Calorific Value)] × 100

High efficiency means better fuel utilization and lower operating cost.

8. What is meant by dry flue gas loss?

Heat loss carried away by dry exhaust gases (mainly CO₂, O₂, N₂).

Occurs due to high flue gas temperature and excess air in combustion.

Represented as a percentage of total heat input.

Formula:

Dry Flue Gas Loss (%) = [(m × Cp × (Tg - Ta)) / (Fuel × GCV)] × 100

Where:

m = mass of dry flue gas (kg/kg of fuel)

Cp = specific heat of flue gas (kJ/kg°C)

Tg = flue gas temperature (°C)

Ta = ambient air temperature (°C)

Reducing flue gas temperature and excess air minimizes this loss.

9. What are the common fuels used in boilers?

Solid fuels: Coal, Biomass, Wood chips, Bagasse.

Liquid fuels: Furnace oil, Diesel, LDO (Light Diesel Oil).

Gaseous fuels: Natural Gas, LPG, Biogas.

Special: Waste heat, hydrogen-rich off-gases in process industries.

Fuel choice depends on availability, cost, and emission standards.

10. What is the function of a steam drum in a boiler?

The steam drum separates steam from water mixture in water-tube boilers.

Maintains water level and steam purity.

Provides space for steam-water separation and collection of saturated steam.

Houses internals like cyclone separators, scrubbers, and demisters.

Ensures steady and dry steam supply to superheaters or process lines.

11. What is the normal operating pressure and temperature of a boiler?

Depends on the boiler type and process requirement.

Low-pressure boilers: up to 25 bar and 250°C (used in industries like textile, food).

High-pressure boilers: 40–150 bar and 400–540°C (used in power and chemical plants).

Steam parameters are designed to match process load and safety limits.

12. What are the start-up and shutdown procedures of a boiler?

Start-up Procedure:

Check all safety valves, water level, and interlocks.

Ensure fuel and air supply are available.

Purge the furnace to remove unburnt gases.

Ignite pilot burner → main burner → raise pressure gradually.

Warm-up lines slowly to avoid thermal shock.

Shutdown Procedure:

Gradually reduce load and stop fuel firing.

Maintain circulation for a few minutes.

Isolate steam and fuel lines.

Allow boiler to cool naturally before maintenance.

13. What are the common boiler maintenance checks?

Daily: Check pressure, temperature, feedwater level, and safety devices.

Weekly: Blowdown tests, burner flame inspection.

Monthly: Check safety valves, controls, leaks, and instruments.

Annually: Internal inspection, hydrostatic test, tube cleaning, and calibration.

Proper preventive maintenance reduces breakdown and improves efficiency.

14. What causes foaming and priming in boilers?

Foaming: Formation of bubbles on water surface due to high TDS or oil contamination.

Priming: Carryover of water droplets with steam due to high water level or sudden load changes.

Prevention:

Maintain correct water chemistry (TDS control).

Use antifoam chemicals and perform regular blowdown.

Avoid rapid load variations.

15. How do you prevent scale and corrosion in boilers?

Use proper feedwater treatment to remove hardness and oxygen.

Maintain pH between 8.5–9.5 for water-tube boilers.

Use chemical dosing – phosphate, sulfite, or hydrazine.

Perform regular blowdown to control TDS.

Maintain deaerator efficiency to eliminate dissolved oxygen.

16. What is blowdown? Why is it necessary?

Blowdown is the removal of a portion of boiler water to control the concentration of impurities.

Necessary to:

Prevent scaling and foaming.

Maintain water quality and TDS limits.

Remove sludge and sediments from the drum bottom.

Types:

Continuous blowdown – automatic and steady.

Intermittent blowdown – manual, at regular intervals.

17. What are the types of blowdown in a boiler?

Intermittent Blowdown:

Manual operation at drum bottom.

Removes sludge and sediments.

Continuous Blowdown:

Small, steady discharge from the steam drum.

Maintains TDS within limits automatically.

Both help in maintaining boiler water purity and efficiency.

18. How do you maintain boiler water quality?

Use softened or demineralized feedwater.

Maintain TDS, pH, hardness, and dissolved oxygen within limits.

Conduct regular water testing (daily or shift-wise).

Control parameters via chemical dosing and blowdown.

Ensure deaerator is working properly to remove gases.

19. What is the purpose of deaeration in boiler feedwater?

Removes dissolved oxygen and carbon dioxide, which cause corrosion.

Improves feedwater temperature, enhancing thermal efficiency.

Reduces shock and thermal stress in the boiler.

Achieved by mechanical deaerator (spray or tray type) with venting of gases.

Typically maintains O₂ content below 0.007 mg/L.

20. What are the typical parameters monitored in boiler water?

Total Dissolved Solids (TDS) – controls scale formation.

pH – controls corrosion (maintain 8.5–9.5).

Hardness (Ca, Mg) – must be near zero.

Dissolved Oxygen (DO) – should be minimal (<0.007 mg/L).

Silica – affects turbine and superheater performance.

Regular testing ensures safe, efficient, and long-term boiler operation.

21. What are boiler safety valves? How do they work?

Safety valves automatically release steam when boiler pressure exceeds the set limit.

Protects the boiler from overpressure and explosion hazards.

Operates on the spring-loaded principle — valve opens when steam pressure > set pressure, and reseats when pressure drops.

Regular testing ensures reliability and compliance with IBR regulations.

Common types: Spring-loaded, Lever type, and High-lift safety valves.

22. What interlocks are provided in a boiler?

Interlocks ensure safe sequential operation and automatic shutdown in abnormal conditions.

Common boiler interlocks include:

Low water level trip

Flame failure trip

High steam pressure trip

FD/ID fan failure trip

Furnace purging interlock before ignition

Fuel pressure or atomizing air pressure low trip

Interlocks prevent unsafe operation and protect both equipment and personnel.

23. What are the safety precautions before starting a boiler?

Check water level in the gauge glass.

Ensure all valves and vents are in correct positions.

Verify safety valve, pressure gauge, and low-level alarms are functional.

Inspect fuel and air systems for leaks.

Perform furnace purge to remove unburnt gases.

Confirm feed pump and cooling systems are operational.

Follow start-up checklist and obtain necessary permits or clearances.

24. What is meant by low-water cutoff?

A low-water cutoff (LWC) is a safety device that shuts down the burner when the boiler water level falls below the safe limit.

Prevents overheating and tube damage.

Usually works via float-type or probe-type level sensors.

Ensures automatic trip and lockout until water level is restored.

25. How do you test the safety valve of a boiler?

Manual testing: Lift the valve lever slightly to ensure it opens and reseats properly.

Pressure testing: Raise boiler pressure to set value and check the valve lift point.

Ensure valve discharge is safe and unobstructed.

Record set pressure and reseating pressure in inspection logs.

Testing must be done under supervision of authorized personnel as per IBR or ASME codes.

26. What is a flame failure? What actions are taken in case of flame failure?

Flame failure occurs when the flame in the furnace extinguishes unexpectedly during operation.

Causes: fuel supply failure, air imbalance, ignition fault, or flame scanner malfunction.

Action:

Burner management system (BMS) trips the boiler automatically.

Initiate post-purge cycle to clear unburnt gases.

Identify cause → rectify → perform safe re-ignition sequence.

Never re-fire without completing the purge process.

27. What are the causes of boiler explosion?

Overpressure due to safety valve failure or blocked steam line.

Low water level causing overheating of tubes.

Poor maintenance or defective welding in pressure parts.

Fuel-air mixture explosion due to flame failure or gas accumulation.

Corrosion or scale formation weakening metal surfaces.

Prevented by regular inspection, interlocks, and trained operation.

28. What are the emergency shutdown conditions for a boiler?

A boiler must be tripped immediately if any of the following occurs:

Low water level alarm/trip

High steam pressure beyond design limit

Flame failure or furnace explosion risk

Feedwater pump failure

ID/FD fan trip causing poor combustion

Safety valve malfunction

Abnormal noise, leakage, or vibration

Operator must act quickly to cut off fuel, isolate steam, and vent safely.

29. How do you handle a boiler tube leak?

Immediately trip the boiler and isolate steam.

Allow boiler to depressurize and cool before inspection.

Identify leak location by hydrostatic or air test.

Replace or plug the damaged tube as per approved repair procedure.

Conduct post-repair hydrotest and NDT (Non-Destructive Testing) before recommissioning.

Analyze root cause — corrosion, erosion, or stress.

30. What are the firefighting measures in case of a boiler fire?

Trip the boiler immediately and isolate fuel supply.

Activate emergency shutdown and fire suppression system.

Use CO₂, dry chemical powder (DCP), or water spray depending on the fire type.

Evacuate area and inform safety team.

After extinguishing, ventilate furnace and inspect damage before restart.

Maintain fire extinguishers, hydrants, and alarms near boiler area at all times.

31. What instruments are used to monitor boiler performance?

Pressure gauge / Transmitter – measures steam and feedwater pressure.

Temperature indicators – monitor flue gas, steam, feedwater temperatures.

Flow meters – measure fuel, air, and steam flow.

Level transmitters – monitor drum and feed tank levels.

Oxygen analyzer – checks excess air for combustion control.

Flue gas analyzer – monitors O₂, CO₂, CO, NOx for efficiency.

Vibration & bearing temperature sensors – protect fans and pumps.

Together, these ensure safe, efficient, and optimized operation.

32. What is the purpose of the feedwater control valve?

Regulates the amount of feedwater entering the boiler drum.

Maintains constant water level to avoid low-water or high-level trips.

Operates automatically through a drum level control loop.

In large boilers, it’s controlled by single-element, two-element, or three-element systems.

Prevents carryover, priming, and maintains steady steam generation.

33. What is a pressure gauge siphon and its purpose?

A U-shaped loop installed between the boiler and pressure gauge.

Filled with water or condensate to protect the gauge from direct steam temperature.

Prevents damage from overheating and pressure pulsations.

Commonly used for steam, superheated steam, and high-pressure lines.

34. How does a boiler control panel work?

The control panel is the central unit for monitoring and controlling all boiler functions.

Displays parameters like pressure, temperature, level, flow, and alarms.

Integrated with PLC/DCS for automation and interlock sequencing.

Manages start-up, shutdown, safety trips, and burner operation.

Ensures safe, automatic, and energy-efficient operation with real-time feedback.

35. What is the purpose of the flame scanner?

Detects the presence and stability of the burner flame.

Prevents fuel accumulation by initiating trip on flame failure.

Works on UV, IR, or combined UV/IR sensing technology.

Sends signal to Burner Management System (BMS) for automatic control.

Vital for boiler safety, fuel efficiency, and compliance with standards.

36. How do you calibrate a pressure switch or transmitter in a boiler?

Isolate the instrument and connect a pressure calibrator or dead-weight tester.

Apply known pressure and check corresponding output signal.

Adjust zero and span to match set calibration range.

Verify at multiple points (0%, 25%, 50%, 75%, 100%).

Record results and tag calibration certificate.

Calibration ensures accurate protection, interlock, and control actions.

37. What is the function of the Burner Management System (BMS)?

BMS ensures safe start-up, operation, and shutdown of the burner.

Controls fuel valves, air dampers, ignition, and flame detection.

Includes purge cycle, ignition sequence, flame monitoring, and trips.

Interlocked with pressure, temperature, and level controls.

Prevents explosions by ensuring no fuel without flame and no flame without air purge.

38. What are interlocks between feed pump and level control?

Prevents dry running or overflow of the boiler drum.

If low-level alarm – feed pump starts automatically.

If high-level alarm – feed pump stops or control valve closes.

Integrated with three-element control system to maintain constant level during load changes.

Protects boiler from tube overheating or water carryover.

39. What is meant by “purging” in a boiler?

Purging means blowing out unburnt fuel and gases from the furnace with air.

Done before ignition (pre-purge) and after flame failure (post-purge).

Ensures the furnace is free from explosive mixtures.

Typically uses FD fan to achieve 4–5 volume changes.

Prevents furnace explosions and ensures safe ignition conditions.

40. Why is a pre-purge and post-purge cycle necessary?

Pre-purge:

Removes combustible gases before ignition.

Ensures fresh air environment for flame stability.

Post-purge:

Clears remaining unburnt fuel after burner shutdown or trip.

Prevents firebox explosion and carbon deposits.

Controlled automatically by BMS through timer-based logic.

Essential for safe combustion and compliance with boiler safety codes.

41. How do you calculate boiler efficiency?

Boiler efficiency measures how effectively the boiler converts fuel energy into useful steam energy.

Formula (Direct Method):

Boiler Efficiency (%) = (Heat Output / Heat Input) × 100

Formula (Indirect Method):

Boiler Efficiency (%) = 100 – (Sum of all losses)

Main losses include:

Dry flue gas loss

Moisture in fuel & air loss

Unburnt carbon loss

Radiation & convection loss

High efficiency = lower fuel consumption & better performance.

42. What is excess air and why is it important?

Excess air is the additional air supplied beyond the stoichiometric requirement for complete combustion.

Ensures complete fuel burning and reduces CO emissions.

Too little → incomplete combustion (CO formation).

Too much → heat loss via flue gases and reduced efficiency.

Optimum range:

Oil/gas boilers: 10–15% excess air

Coal-fired: 20–30% excess air

Maintaining optimum excess air is key to high efficiency and low emissions.

43. How do you measure and control stack temperature?

Stack (flue gas) temperature is measured using thermocouples or RTDs at the boiler outlet.

Indicates heat losses and combustion performance.

High stack temperature → poor heat transfer or soot fouling.

Low stack temperature → risk of condensation and corrosion.

Controlled by cleaning heat surfaces, proper air-fuel ratio, and economizer performance.

44. What are the common causes of reduced boiler efficiency?

Poor combustion due to incorrect air-fuel ratio.

Soot or scale buildup on heat transfer surfaces.

High flue gas temperature (wasted heat).

Poor feedwater quality leading to scaling.

Excess blowdown or steam leakage.

Low load operation for extended periods.

Regular maintenance and tuning restore optimal efficiency.

45. What methods are used to improve boiler efficiency?

Install economizer to recover heat from flue gases.

Use air preheater to warm combustion air.

Maintain optimum excess air using O₂ analyzer.

Implement condensate recovery to reuse hot water.

Perform regular soot blowing and descaling.

Optimize boiler loading near design point.

Conduct periodic efficiency tests (direct/indirect method).

46. What is heat rate in a boiler system?

Heat rate is the amount of heat energy required to produce one unit of steam energy or power output.

Lower heat rate means better efficiency.

Formula:

Heat Rate = (Heat Input in kCal/hr) / (Steam Output in kCal/hr or Power Output in kWh)

Example: A lower heat rate indicates improved fuel utilization and performance consistency.

47. What is the effect of soot deposition on heat transfer?

Soot acts as an insulating layer on heat transfer surfaces.

Reduces heat absorption efficiency and increases flue gas temperature.

Leads to higher fuel consumption and lower efficiency.

Regular soot blowing or online cleaning is essential to maintain performance.

48. What are energy-saving opportunities in boiler operation?

Recover heat from flue gases (economizer, air preheater).

Condensate recovery and flash steam utilization.

Variable frequency drives (VFDs) for fans and pumps.

Automatic blowdown control to reduce heat loss.

Boiler insulation maintenance to prevent radiation losses.

Regular combustion tuning using O₂ & CO analyzers.

Waste heat recovery from exhaust streams.

49. How is fuel consumption monitored and controlled?

Measured using flow meters (mass or volumetric type).

Data logged through PLC/DCS for energy accounting.

Controlled via combustion control system (CCS) adjusting air/fuel ratio.

Periodic checks of calorific value (CV) and specific fuel consumption (SFC) ensure accuracy.

Continuous monitoring helps in efficiency benchmarking and cost reduction.

50. What are the main parameters recorded in a boiler log sheet?

Steam pressure and temperature

Feedwater temperature

Fuel and air flow rates

Flue gas temperature and O₂ level

Boiler water level and TDS

Blowdown quantity and frequency

Efficiency data (periodic)

Maintaining an accurate log ensures traceability, performance tracking, and early problem detection.

51. What are the statutory requirements for boiler operation (as per IBR)?

All boilers operating above 1 bar pressure and producing steam must comply with IBR – Indian Boiler Regulations, 1950.

Must have a valid Certificate of Inspection and Fitness issued by an authorized Boiler Inspector.

Boiler operation must be supervised by a certified Boiler Attendant or Engineer.

Safety valves, pressure gauges, and blowdown valves must meet IBR standards.

Records of operation, maintenance, and inspection must be maintained and available for audit.

52. What is IBR (Indian Boiler Regulations)?

IBR governs design, construction, operation, and inspection of boilers in India.

Ensures safe manufacturing, installation, and operation of boilers under the Boiler Act, 1923.

Covers:

Material selection and welding standards

Design pressure calculations

Testing and certification requirements

Competency of boiler operators

Enforced by Chief Inspector of Boilers (CIB) in each state.

53. What are the documents required for boiler inspection?

Boiler registration certificate

Manufacturer’s test certificate for pressure parts

Previous inspection report and maintenance logbook

Calibration records of safety instruments

Boiler water analysis reports

Operating and maintenance manuals

Form II, III, and IV as per IBR documentation requirements.

Having these ensures smooth inspection and quick certification renewal.

54. Who is a certified boiler attendant?

A licensed professional authorized to operate boilers as per IBR Rules.

Must hold a First Class or Second Class Boiler Attendant Certificate issued by the Boiler Board.

Responsible for safe start-up, operation, monitoring, and emergency handling.

Must ensure compliance with statutory and safety requirements.

55. What are the frequency and scope of boiler inspections?

Annual Inspection:

Comprehensive internal and external inspection.

Includes safety valves, tubes, drums, mountings, and controls.

Hydrostatic Test:

Done after major repair or as required by the inspector.

Certification Validity:

Usually 12 months, extendable upon satisfactory inspection.

Daily & Monthly checks must be performed by operators as per O&M manual.

56. What is the hydrostatic test pressure for a boiler?

A hydrostatic test checks the strength and leak-tightness of pressure parts.

Carried out at 1.25 to 1.5 times the design pressure (as per IBR).

Water is used as the test medium (not air or steam).

Pressure held for 30 minutes while inspecting for leaks or deformation.

Successful test confirms boiler’s mechanical integrity and safety readiness.

57. What safety certificates are required for a boiler?

Boiler Registration Certificate (Form V) – after first inspection.

Certificate of Fitness (Form VI) – after annual inspection.

Boiler Attendant License – for operation personnel.

Safety Valve Test Certificate – after calibration and inspection.

NDT/Thickness Reports – for old boilers or after repair.

All certificates must be valid and displayed near the boiler.

58. How do you prepare a boiler for annual inspection?

Shutdown and cool down the boiler.

Drain all water and clean internal surfaces.

Open manholes and handholes for access.

Remove scale, soot, and deposits.

Ensure safety valves, gauges, and fittings are accessible.

Provide adequate ventilation and lighting for inspection.

Keep test records and maintenance reports ready for the inspector.

59. What are the penalties for operating without certification?

Operating an unregistered or uncertified boiler violates the Boiler Act, 1923.

May result in legal prosecution, fines, or shutdown orders.

Heavy penalties can include:

₹1 lakh fine or more depending on state laws.

Immediate sealing of the boiler by the inspector.

Non-compliance can also void insurance and liability coverage.

60. What are the responsibilities of a boiler operator under IBR?

Operate and maintain the boiler within safe limits of pressure and temperature.

Ensure all safety devices and interlocks are functional.

Maintain logbook of readings and blowdown records.

Conduct routine water analysis and maintain TDS levels.

Report any abnormality, leak, or unsafe condition immediately.

Follow statutory compliance and cooperate during inspections.

61. What causes low steam pressure in a boiler?

Insufficient fuel supply or combustion air.

Feedwater pump malfunction affecting steam generation.

Excessive steam demand beyond boiler capacity.

Soot or scale deposits reducing heat transfer.

Faulty pressure control valve or leaking safety valve.

Action: Check fuel, air, and load balance; clean heat surfaces; verify controls.

62. What causes high stack temperature?

Soot accumulation on heat transfer surfaces.

Poor heat recovery due to economizer or air preheater fouling.

Excess air in combustion.

Low water flow through economizer.

Tube scaling on water side.

Action: Perform soot blowing, check economizer flow, adjust air-fuel ratio.

63. What are the signs of a boiler tube leakage?

Sudden drop in drum pressure and water level.

Hissing sound or visible steam from casing.

White smoke or vapor from stack.

Abnormal feedwater consumption.

Wet ash in furnace bottom.

Action: Trip the boiler, isolate section, allow cooling, and inspect leak.

64. What causes flame instability in a boiler?

Improper air-fuel ratio or low fuel pressure.

Draft imbalance due to FD/ID fan malfunction.

Poor burner atomization or dirty nozzles.

Fluctuating steam load or back pressure.

Faulty flame scanner or misalignment.

Action: Adjust air-fuel settings, inspect burner and fans, recalibrate scanner.

65. What is carryover and how do you control it?

Carryover is the entrainment of water droplets with steam.

Caused by high drum level, sudden load change, or foaming.

Leads to wet steam, erosion, and turbine damage.

Control measures:

Maintain correct water level and TDS.

Use steam separators and antifoam chemicals.

Avoid rapid load variations and perform blowdown regularly.

66. What causes black smoke from the chimney?

Incomplete combustion due to insufficient air or poor fuel atomization.

Dirty burner tips or clogged filters.

Low furnace temperature or excess fuel feed.

Poor mixing of air and fuel.

Action: Check air register, burner, atomizing steam/air pressure, and tune the burner.

67. What causes water hammer in the steam line?

Formation of condensate slugs moving at high velocity.

Improper drainage or trapping of condensate.

Sudden valve opening/closing or rapid startup.

Leads to pipe vibration, noise, and mechanical damage.

Control: Install proper steam traps, drain pockets, and gradual start-up.

68. How do you detect and control air leakage in a boiler?

Detection: Observe negative pressure variation, smoke ingress, or CO₂/O₂ analysis deviation.

Common areas: Flue gas duct joints, expansion bellows, casing, and manholes.

Control: Seal leaks using high-temp sealing compound or gasket replacement.

Regular inspection during shutdown and thermal audit helps minimize losses.

69. What actions do you take during boiler tripping?

Immediately isolate fuel and air systems.

Acknowledge trip alarms and identify root cause.

Perform post-purge to remove residual gases.

Verify water level, pressure, and temperature before restart.

Record event in logbook and rectify cause before re-firing.

Never bypass interlocks or restart without root cause analysis.

70. How do you troubleshoot a feedwater pump failure?

Check electrical supply and motor overloads.

Inspect suction valve, strainer, and NPSH (cavitation).

Verify feedwater tank level and deaerator pressure.

Check mechanical seal or coupling failure.

Switch to standby pump immediately.

Post-troubleshooting: Analyze for repeated failures and maintain lubrication and alignment.

71. What are the main emissions from a boiler?

Boilers emit pollutants depending on fuel type and combustion efficiency.

Main emissions include:

CO₂ – from complete combustion of carbon.

CO – from incomplete combustion.

NOx (Nitrogen Oxides) – from high-temperature oxidation of nitrogen.

SOx (Sulfur Oxides) – from sulfur in fuel.

Particulate Matter (PM) – from ash and unburnt carbon.

Control: Optimize combustion, use clean fuel, and install emission control devices.

72. What are the permissible emission limits for boilers?

Defined by CPCB (Central Pollution Control Board) and SPCB (State Boards) under the Environment (Protection) Rules, 1986.

Typical limits (for small/medium industrial boilers):

PM: 150 mg/Nm³ (solid fuel), 50 mg/Nm³ (oil/gas).

SO₂ and NOx: 100–400 mg/Nm³ depending on fuel and capacity.

CO: <150 mg/Nm³ for gas/oil-fired boilers.

Actual limits vary by fuel, capacity, and location — always refer to the latest CPCB notification.

73. How does sulfur content in fuel affect emissions?

High sulfur content → higher SO₂ formation.

Leads to acidic flue gas, corrosion, and environmental pollution.

Increases acid rain potential.

Control methods:

Use low-sulfur fuel or desulfurization systems (FGD).

Add limestone or dolomite in fluidized bed boilers to absorb sulfur.

74. What methods are used to reduce NOx emissions?

Low NOx burners – control flame temperature and fuel-air mixing.

Flue Gas Recirculation (FGR) – recycles cooled gases to reduce combustion temperature.

Staged combustion – divides air supply to reduce NOx formation.

Water or steam injection – lowers flame temperature.

Selective Catalytic Reduction (SCR) or Non-Catalytic Reduction (SNCR) – converts NOx to N₂ and H₂O using ammonia or urea.

75. What is Flue Gas Desulfurization (FGD)?

A process to remove sulfur oxides (SO₂/SO₃) from flue gases before emission.

Wet FGD: Uses limestone slurry to absorb SO₂ → forms gypsum (CaSO₄·2H₂O).

Dry FGD: Uses lime or sodium bicarbonate injection.

Benefit: Reduces acid rain, corrosion, and meets emission norms.

Common in coal-fired and heavy oil-fired industrial boilers.

76. What is an ESP (Electrostatic Precipitator) and how does it work?

ESP removes particulate matter (dust and ash) from flue gas using electrostatic forces.

Working Principle:

Flue gas passes between charged electrodes → dust particles get charged → migrate to collector plates.

Periodically rapped off and collected as ash.

✅ Efficiency: up to 99% dust removal.

✅ Used in large coal or biomass-fired boilers for pollution control.

77. What is the function of a bag filter system?

Bag filters (Fabric filters) trap fine dust particles from flue gas.

Gas passes through fabric bags, and dust accumulates on the surface.

Periodically cleaned by reverse air or pulse-jet system.

✅ High efficiency for PM control (<50 mg/Nm³).

✅ Common in small industrial boilers and process heating units.

78. What are condensate recovery systems and their benefits?

System to collect and reuse condensate from steam users.

Benefits:

Saves energy and water.

Reduces fuel consumption and boiler blowdown.

Lowers make-up water and chemical costs.

Improves overall plant efficiency by 10–15%.

✅ Typically, condensate temperature ranges from 80–100°C and is directly reused as feedwater.

79. How do you ensure energy conservation in the boiler house?

Regular boiler efficiency monitoring (using flue gas analyzer).

Maintain optimum air-fuel ratio using O₂ trim.

Install economizers and air preheaters.

Implement condensate and flash steam recovery.

Use automatic blowdown controls.

Monitor fuel-to-steam ratio and heat rate monthly.

Conduct periodic energy audits and implement findings.

80. How do you reduce carbon footprint in boiler operation?

Switch to clean fuels (natural gas, biomass, hydrogen blends).

Improve combustion efficiency to lower CO₂ per ton of steam.

Recover waste heat for preheating or power generation.

Recycle condensate and minimize losses.

Implement energy management systems (ISO 50001).

Use renewable-assisted systems like solar feedwater preheating.

81. What is the function of the furnace in a boiler?

The furnace (combustion chamber) is where fuel is burned to generate heat.

Transfers heat to the water and steam circuits via radiation and convection.

Must maintain proper air-fuel ratio for complete combustion.

Designed with refractory lining to withstand high temperature and prevent heat loss.

82. What materials are used for boiler tubes?

Tubes must resist high pressure, temperature, and corrosion.

Common materials:

Carbon Steel (SA-210, SA-192) – for low to medium temperature.

Alloy Steel (T11, T22) – for high-pressure, high-temperature areas (superheater).

Stainless Steel (TP304, TP316) – for corrosive environments.

Material selection follows ASME Section II and IBR standards.

83. What is meant by the “steam generation rate”?

Amount of steam produced per hour per unit heating surface or fuel input.

Formula:

Steam Generation Rate = (Steam Output in kg/hr) / (Heating Surface Area in m²)

Indicates boiler capacity and heat transfer efficiency.

Higher rates require better circulation and heat flux control.

84. What are the typical design pressures for water-tube and fire-tube boilers?

Fire-tube boilers: up to 25 bar (low to medium pressure).

Water-tube boilers: 40–150 bar or higher (high-pressure and supercritical).

Design pressure includes 10–25% safety margin above operating pressure.

As per IBR and ASME Section I requirements.

85. What are the common types of drum arrangements in boilers?

Single Drum Boiler: Compact, used for low/medium capacity.

Bi-Drum Boiler: Two drums (steam & water), used for high-pressure systems.

Twin Drum Boiler: Parallel drums connected by riser and downcomer tubes.

Vertical Drum: For compact package units.

✅ Selection depends on steam pressure, load variation, and design complexity.

86. What is a downcomer and riser in a boiler?

Downcomer: Carries cooled, dense water from steam drum to bottom headers.

Riser (Water wall tubes): Carries heated water-steam mixture upward to the drum.

Together they form natural circulation loops due to density difference.

Ensures uniform heat absorption and prevents tube overheating.

87. Why is a boiler designed for a specific pressure and temperature?

To ensure mechanical strength and safety margin under working conditions.

Pressure and temperature determine material selection, thickness, and weld design.

Overdesign leads to high cost; underdesign leads to safety risks.

Based on ASME Section I / IBR design equations for pressure parts.

88. What is the difference between saturated and superheated steam?

Saturated steam: Steam at boiling point corresponding to its pressure, contains no superheat.

Superheated steam: Steam heated beyond its saturation temperature.

Superheated steam is dry, used for turbines and power generation.

Increases efficiency and prevents condensation losses.

89. What are the main differences between high-pressure and low-pressure boilers?

High-pressure boiler: Operates above 25 bar; uses water-tube design, high efficiency, and forced circulation.

Low-pressure boiler: Operates below 25 bar; fire-tube design, simple operation.

HP boilers require advanced metallurgy, automation, and strict water treatment.

LP boilers are used for heating and small process applications.

90. What is a condensing boiler?

A condensing boiler recovers latent heat from flue gas moisture.

Condenses water vapor in exhaust gas to extract hidden heat of vaporization.

Achieves efficiency up to 95–98%.

Common in natural gas-fired systems with low return water temperature.

Reduces CO₂ emissions and fuel cost.

91. What is the importance of the air-fuel ratio in combustion?

Determines completeness of combustion and fuel efficiency.

Too little air → incomplete combustion, CO and soot.

Too much air → heat loss through flue gases.

Ideal ratio:

Natural gas: ~10:1

Oil: ~14:1

Coal: ~18–20:1

Maintaining optimum ratio ensures maximum efficiency and minimum emissions.

92. What is the significance of boiler turndown ratio?

The ratio of maximum to minimum load at which a boiler can operate efficiently.

Indicates load flexibility without affecting flame stability or efficiency.

Typical values:

Gas-fired: 8:1 to 10:1

Oil-fired: 4:1 to 6:1

Higher turndown = better load-following capability and fuel savings.

93. Why are baffles used inside boilers?

Baffles direct flue gas flow across tube banks for better heat transfer.

Prevent short-circuiting of hot gases.

Help maintain uniform gas velocity and improve thermal efficiency.

Usually made of mild steel or refractory material.

94. What are the typical heat losses in a boiler system?

Dry flue gas loss – major (5–10%)

Unburnt fuel loss – 1–2%

Moisture in fuel & hydrogen combustion loss – 3–5%

Radiation and convection loss – 1–2%

Blowdown loss – 1–3%

Minimizing these through maintenance, insulation, and combustion control boosts efficiency.

95. What is radiant heat and convective heat in boiler design?

Radiant heat: Heat transfer via electromagnetic radiation from flame and hot gases to water walls.

Convective heat: Heat transfer through fluid motion of flue gases over tube surfaces.

Modern boilers use radiant sections (furnace) and convective passes (superheater, economizer) for efficient design.

96. What is the purpose of refractory material in boilers?

Protects furnace walls from high-temperature flame and corrosion.

Minimizes heat losses and maintains stable furnace temperature.

Must have high melting point, strength, and thermal shock resistance.

Common materials: Fireclay, alumina, magnesia bricks.

97. What is the function of the steam separator?

Separates moisture and water droplets from the steam.

Ensures dry steam supply to process or turbine.

Works by centrifugal or baffle-type separation.

Improves efficiency and prevents erosion in downstream equipment.

98. What is a fluidized bed boiler?

Uses air blown through a bed of solid particles (like sand or ash) to suspend them.

Enhances fuel-air contact for efficient combustion.

Can burn low-grade fuels with high ash content.

Types: AFBC (Atmospheric) and CFBC (Circulating Fluidized Bed).

Provides low emissions and uniform heat distribution.

99. What is the advantage of using a water-tube boiler over a fire-tube boiler?

Handles higher pressure and temperature.

Provides faster steam generation and better heat transfer.

Easier to clean and maintain.

Suitable for large industrial or power applications.

Safer — smaller water content, less risk of explosion.

100. What is the difference between a package boiler and a field-erected boiler?

Package Boiler:

Factory-assembled and skid-mounted.

Quick installation and compact design.

Used for small to medium capacities.

Field-Erected Boiler:

Assembled on site for large capacities (>50 TPH).

Custom design flexibility, suitable for power and process plants.

✅ Choice depends on capacity, project timeline, and layout constraints.

101. What are the types of burners used in boilers?

Pressure Jet Burner: Uses fuel pressure to atomize oil (common in small to medium boilers).

Air or Steam Atomized Burner: Uses compressed air or steam for fine atomization (used in large boilers).

Rotary Cup Burner: Uses centrifugal force to atomize viscous fuel.

Gas Burner: Mixes gas and air in correct proportion for clean combustion.

Dual-Fuel Burner: Can operate on both gas and oil; ideal for reliability.

102. What is the purpose of primary and secondary air in combustion?

Primary Air:

Mixes directly with fuel for ignition and stable flame.

Controls fuel-air ratio and affects flame temperature.

Secondary Air:

Provides oxygen for complete combustion.

Helps control flame shape and turbulence.

✅ Proper balance avoids CO formation and maximizes efficiency.

103. How is atomization achieved in oil-fired boilers?

Atomization breaks oil into fine droplets for complete combustion.

Achieved by:

Pressure Atomization: High fuel pressure through small orifice.

Air/Steam Atomization: Mixing fuel with high-velocity air or steam jet.

Rotary Cup Atomization: Centrifugal force in rotating cup spreads fuel film.

✅ Finer atomization ensures cleaner burning and lower unburnt carbon.

104. What is meant by complete and incomplete combustion?

Complete Combustion: All fuel carbon converts to CO₂ and hydrogen to H₂O.

Results in maximum heat release, clean flame, and high efficiency.

Incomplete Combustion: Lack of air causes CO, soot, or unburnt hydrocarbons.

Leads to energy loss and pollution.

✅ Controlled air-fuel ratio ensures complete combustion.

105. What is the purpose of the air register in a boiler?

Controls the air flow and swirl entering the burner.

Ensures uniform mixing of fuel and air.

Maintains stable flame and prevents backfire or flame impingement.

Adjustable vanes or dampers are used to fine-tune the flame shape.

106. What are the causes of black smoke from the stack?

Insufficient air supply or low atomizing pressure.

Dirty burner tips or clogged filters.

Low furnace temperature or excessive fuel feed.

Poor fuel quality or improper flame adjustment.

✅ Remedy: Clean burners, adjust air registers, check atomizing system, and tune combustion.

107. What are the main causes of unburnt carbon in ash?

Poor fuel-air mixing or low furnace temperature.

Large fuel size or uneven distribution in the furnace.

Insufficient residence time of fuel particles.

Malfunctioning burners or nozzles.

✅ Regular tuning, correct excess air, and proper fuel size minimize unburnt carbon losses.

108. What are the advantages of using natural gas over furnace oil?

Higher combustion efficiency and clean burning.

No soot or ash generation.

Faster heat response and simpler control.

Lower maintenance cost and reduced emissions (NOx, SOx, CO₂).

No fuel storage or handling hazards.

✅ Ideal for modern, automated, and low-emission boiler systems.

109. What is flue gas recirculation (FGR) and why is it used?

A portion of flue gas is recirculated to the burner inlet to lower flame temperature.

Reduces formation of thermal NOx by diluting oxygen.

Improves flame stability and combustion control.

Widely used in gas- and oil-fired low-NOx boilers.

110. How is combustion efficiency measured?

Determined by flue gas analysis using a combustion analyzer.

Parameters:

O₂, CO₂, CO, NOx, SO₂, and stack temperature.

Higher CO₂ and lower O₂ indicate better combustion.

Formula:

Combustion Efficiency (%) ≈ 100 – (Heat loss in dry flue gas + moisture + unburnt losses)

✅ Regular monitoring helps optimize fuel consumption.

111. What is the importance of flue gas analysis?

Indicates combustion performance and air-fuel balance.

Detects excess air, incomplete combustion, or air leakage.

Guides burner tuning and efficiency optimization.

Key parameters: O₂, CO₂, CO, and flue temperature.

✅ Used routinely in energy audits and emission compliance checks.

112. What is an oxygen analyzer used for?

Measures O₂ content in flue gases continuously.

Helps maintain optimum excess air via O₂ trim control.

Reduces fuel loss and improves efficiency.

Installed at boiler outlet or economizer exit.

✅ Typical range: 2–5% O₂ for gas/oil boilers, 5–8% for solid fuel boilers.

113. How does an automatic combustion control system work?

Monitors and controls fuel and air flow based on steam demand.

Adjusts dampers and valves using PID control logic.

Maintains steady steam pressure and O₂ level.

Minimizes human error and improves efficiency and safety.

✅ Key part of Boiler Automation (CCS + BMS).

114. What is the typical range of excess air required for good combustion?

Natural Gas: 10–15%

Oil: 15–20%

Coal/Biomass: 25–40%

✅ Too low → CO formation; too high → flue gas losses.

Maintaining optimum O₂ in flue gas (2–6%) ensures efficient combustion.

115. What causes yellow or smoky flames in a boiler furnace?

Inadequate air or poor mixing.

Low atomizing pressure in oil burners.

Clogged or worn burner nozzles.

Improper fuel temperature (for viscous oils).

✅ Remedy: Adjust air registers, clean burners, maintain correct atomization pressure.

116. What is flame impingement and why is it dangerous?

Occurs when the flame directly touches boiler tubes or walls.

Causes localized overheating, tube damage, and metal failure.

Results from improper burner alignment or excess fuel flow.

✅ Correct burner angle and maintain proper air-fuel ratio and flame shape.

117. How do you adjust the burner flame shape?

By varying air register vanes and fuel pressure.

Adjust primary and secondary air to get stable blue flame with no smoke.

Observe flame through sight glass; avoid long yellow or lifting flame.

Follow OEM tuning procedure for optimum combustion.

118. What is the role of ID and FD fans in boilers?

FD (Forced Draft) Fan: Supplies combustion air to the furnace.

ID (Induced Draft) Fan: Extracts flue gases and maintains furnace draft (slightly negative).

Together they control airflow, draft pressure, and combustion balance.

✅ Proper coordination prevents backfire and ensures flame stability.

119. What is the purpose of the air preheater bypass damper?

Allows flue gases to bypass the air preheater during startup or low-load operation.

Prevents low-temperature corrosion from flue gas condensation.

Helps control air temperature and combustion stability during varying loads.

✅ Used in large boilers with regenerative or tubular air preheaters.

120. What causes flame blow-off or flashback?

Blow-off: Flame lifted off burner tip due to excess air velocity.

Flashback: Flame burns inside burner tube due to low air velocity or gas leak.

Caused by improper air-fuel ratio, draft imbalance, or nozzle damage.

✅ Maintain correct air velocity, pressure, and ensure proper burner design and maintenance.

121. What are the impurities found in boiler feedwater?

Dissolved solids: Calcium, magnesium, sodium, chlorides, sulfates.

Suspended solids: Sand, silt, organic matter.

Dissolved gases: Oxygen (O₂) and carbon dioxide (CO₂).

Oil or organic contamination from process condensate.

✅ These impurities cause scaling, corrosion, and foaming, so proper treatment is essential.

122. What are the problems caused by dissolved oxygen in boiler water?

Oxygen causes pitting corrosion on boiler tubes and drum surfaces.

Forms iron oxide (rust) leading to metal thinning and tube failure.

Corrosion is faster at high temperature and pressure.

✅ Prevented by deaeration and oxygen scavengers like hydrazine or sodium sulfite.

123. What is meant by alkalinity in boiler water?

Alkalinity represents bicarbonates, carbonates, and hydroxides in boiler water.

Controls pH and prevents acid corrosion.

Measured as mg/L CaCO₃ equivalent.

✅ Maintain total alkalinity within 100–300 mg/L depending on pressure to avoid scaling or foaming.

124. What is the ideal pH for boiler water?

For low-pressure boilers: 10.5–11.0

For high-pressure boilers: 9.0–9.5

Slightly alkaline water prevents corrosion and scaling.

✅ Controlled by dosing phosphate or caustic soda in feedwater.

125. What is phosphate treatment in boilers?

Phosphate dosing converts hardness salts (Ca²⁺, Mg²⁺) into soft, non-adherent sludge.

Prevents scale formation on tubes.

Common chemicals: Trisodium phosphate (Na₃PO₄) or Disodium phosphate (Na₂HPO₄).

✅ Must maintain correct alkalinity and phosphate ratio to prevent caustic embrittlement.

126. How do you control silica in boiler water?

Silica forms hard glassy deposits on superheaters and turbines.

Controlled by:

Demineralization (DM plant) of feedwater.

Continuous blowdown to limit concentration.

Typical permissible limit:

<1 ppm for high-pressure boilers.

✅ Regular silica monitoring ensures turbine safety.

127. What is the purpose of condensate polishing?

Removes impurities and corrosion products from condensate return.

Uses ion-exchange resins (mixed-bed units).

Prevents contamination of feedwater and scaling in the boiler.

✅ Maintains high purity condensate (<0.1 µS/cm conductivity).

128. What causes carryover in boilers?

High drum level, foaming, or priming.

High TDS and poor water quality.

Sudden load changes or poor drum internals.

✅ Controlled by maintaining TDS limits, drum level control, and using anti-foam agents.

129. What is sludge and how is it removed from the boiler?

Sludge is the soft deposit formed by precipitated solids at the drum bottom.

Caused by hardness salts, phosphate reaction, and suspended solids.

Removed by intermittent blowdown from the bottom of the boiler drum.

✅ Prevents tube overheating and scaling.

130. How do you test for hardness in boiler water?

Hardness is tested by EDTA titration method.

Indicator: Eriochrome Black T.

Expressed as mg/L (ppm) of CaCO₃.

✅ Feedwater hardness should be near zero (<1 ppm) to prevent scaling.

131. What is a three-element feedwater control system?

Advanced level control system using three variables:

1. Steam flow (load)

2. Feedwater flow

3. Drum water level

Maintains constant water level even during load fluctuations.

✅ Provides accurate control in high-pressure or large-capacity boilers.

132. What are the three elements in the three-element control system?

1. Drum Level Transmitter – measures actual level.

2. Steam Flow Transmitter – compensates for steam outflow.

3. Feedwater Flow Transmitter – adjusts inflow accordingly.

✅ Together, they stabilize the water level and prevent “swell and shrink” effects.

133. What is a differential pressure transmitter and where is it used?

Measures pressure difference between two points.

Used for drum level measurement, flow, and draft control.

In drum level, one side senses steam space, the other water space.

✅ Ensures accurate measurement even with pressure or temperature changes.

134. How does an electronic level transmitter work?

Uses differential pressure, capacitance, or radar principles.

Converts level changes into an electrical signal (4–20 mA).

Output fed to controller or PLC for automatic control.

✅ Provides accurate and continuous level monitoring.

135. What is a drum level control system?

Maintains steady water level in the steam drum.

Prevents low-level (tube overheating) and high-level (carryover).

Operates in:

Single-element (manual or small boilers).

Two-element (medium pressure).

Three-element (high pressure and large load variation).

136. What is the difference between ON/OFF and modulating control?

ON/OFF Control: Feed pump runs when level is low and stops when high. Simple but less accurate.

Modulating Control: Continuously adjusts feedwater valve or pump speed to maintain precise level.

✅ Modulating systems provide smooth control and higher efficiency.

137. What is a PLC and how is it used in boiler automation?

Programmable Logic Controller (PLC): Microprocessor-based control unit.

Executes logic for startup, interlocks, trips, and control loops.

Monitors pressure, level, temperature, flame, and safety devices.

✅ Ensures automatic operation, safety integrity, and consistent performance.

138. What is the function of a flame detector or UV scanner?

Detects the presence and stability of the flame in the furnace.

UV type: Senses ultraviolet radiation (gas flames).

IR type: Detects infrared radiation (oil flames).

If flame fails → signal to BMS to trip the burner immediately.

✅ Prevents unburnt fuel accumulation and explosion.

139. What is the function of the Pressure Reducing Station (PRS)?

Reduces steam pressure to suit process requirements.

Consists of control valve, safety valve, strainer, and gauge.

Maintains constant downstream pressure regardless of upstream fluctuation.

✅ Prevents damage to downstream equipment and saves energy.

140. How do you ensure redundancy in critical boiler instruments?

Provide dual transmitters for pressure, temperature, and level.

Use 2oo3 (two out of three) logic for safety-critical loops.

Ensure independent power and signal paths.

Periodically test each channel for reliability.Redundancy ensures fail-safe operation and continuous boiler availability.

141. What will you do if steam pressure suddenly drops?

Check fuel and air flow — ensure proper combustion.

Verify steam demand — sudden load increase may cause drop.

Inspect safety valve — ensure it’s not leaking or lifted.

Check feedwater flow and drum level — low water can reduce steaming rate.

✅ Action: Balance load and fuel input gradually, avoid thermal stress.

142. What are the reasons for high stack temperature?

Soot formation on heat surfaces.

Tube scaling on water side.

Excess air in combustion.

Economizer malfunction or bypass open.

✅ Action: Clean soot, maintain water chemistry, and check air-fuel settings.

143. What causes a boiler to trip frequently?

Low water level or flame failure.

High steam pressure or over-temperature.

Fan failure (FD/ID fan trip).

Instrument calibration error triggering false trips.

✅ Action: Analyze trip logs, verify interlocks, and recalibrate sensors.

144. What is your action if the feed pump trips during operation?

Immediately start the standby pump.

Monitor drum level closely.

If water level drops below low-level trip → boiler must shut down automatically.

Identify root cause — power, motor, or mechanical failure.

✅ Never bypass the feed pump trip interlock.

145. What should you check if the flame scanner gives a false trip?

Dirty or misaligned scanner lens.

Weak flame signal due to low fuel or poor air adjustment.

Scanner cable damage or electrical interference.

✅ Clean lens, realign, and recalibrate scanner sensitivity.

146. What could cause excessive vibration in ID or FD fans?

Imbalanced impeller or damaged blades.

Bearing wear or shaft misalignment.

Dust or soot buildup on fan blades.

Loose foundation bolts.

✅ Immediate Action: Isolate fan, inspect mechanically, and re-balance before restart.

147. What are the symptoms of a leaking boiler tube?

Abnormal water level fluctuation.

Steam from casing or stack.

Wet ash or hissing noise near furnace.

Increased feedwater consumption.

✅ Trip boiler immediately, cool down, and perform hydrotest.

148. What is the first step during a boiler fire emergency?

Trip the boiler immediately.

Shut off fuel valves and stop the burner.

Activate emergency firefighting system (CO₂ or DCP).

Ventilate furnace after fire is extinguished.

✅ Never open boiler doors until pressure and temperature drop safely.

149. What documents or records must be maintained for safe boiler operation?

Boiler logbook – daily readings (pressure, temperature, TDS, blowdown).

Maintenance records – calibration, inspection, and repair logs.

Water test reports – feedwater and condensate quality.

Trip and alarm history – event log for analysis.

✅ Records help during audits, RCA, and compliance inspections.

150. What lessons can be learned from past boiler explosions or near-misses?

Never operate with faulty safety valves or interlocks.

Never fire a boiler without proper purging.

Ensure operator competency and periodic training.

Regular inspection and preventive maintenance avoid disasters.

✅ Human error and neglect of safety devices are the leading causes of boiler accidents.

151. What will you do if boiler drum level rises abnormally?

Check feedwater control valve — may be stuck open.

Verify steam load — sudden drop can cause swell.

Reduce feedwater flow manually.

Check level transmitter for false high reading.

✅ Maintain level within safe limits to avoid carryover.

152. What will you do if boiler drum level drops suddenly?

Start standby feed pump.

Check for leakage or blowdown valve left open.

Stop firing immediately if low-water trip doesn’t activate.

✅ Dry running leads to tube failure — always treat low level as emergency.

153. What are the signs of poor combustion?

Black smoke or yellow flame.

High CO or unburnt carbon in flue gas.

Increased fuel consumption.

Soot deposition and high stack temperature.

✅ Tune burner and check atomization, air registers, and O₂ trim system.

154. What causes high flue gas O₂ readings?

Excess air or air leakage in ducts.

Damaged seals or loose doors.

Fan imbalance or damper misadjustment.

✅ Inspect system, correct leakage, and tune combustion for optimal O₂ (2–5%).

155. What should be done if the economizer outlet temperature is too high?

Soot deposits or low water flow through economizer.

Blocked tubes or inefficient heat transfer.

✅ Perform soot blowing and check feedwater flow rate.

Maintain outlet temperature ~20–30°C below flue gas temperature.

156. What are the causes of tube overheating?

Low water flow or water starvation.

Scale or soot deposits insulating the tube surface.

Poor circulation or blocked risers.

Flame impingement or misaligned burners.

✅ Ensure proper water chemistry, flow, and regular cleaning.

157. What are common causes of boiler water foaming?

High TDS or oil contamination in water.

Improper chemical dosing.

High alkalinity (>700 mg/L).

✅ Perform blowdown, treat water properly, and maintain chemical balance.

158. What will you do if the safety valve continuously leaks?

Check for dirt or scale on valve seat.

Verify set pressure calibration.

Inspect spring tension or guide misalignment.

✅ Never hammer or tamper the valve. Isolate and replace/repair under supervision.

159. What could cause continuous operation of feedwater pumps?

Leaking feed control valve or faulty level transmitter.

High blowdown rate or leakage in economizer lines.

Steam demand fluctuation with improper control loop tuning.

✅ Tune level controller and inspect valve sealing.

160. What are the causes of high differential pressure across the superheater?

Tube blockage or soot accumulation.

Ash deposits increasing resistance.

Improper soot blowing.

✅ Action: Isolate and clean the superheater section; monitor flue gas velocity.

161. What is a boiler performance test?

A boiler performance test evaluates its efficiency and capacity under actual operating conditions.

Conducted to measure:

Steam output

Fuel input

Efficiency and heat losses

Methods:

Direct method (heat output/heat input)

Indirect method (by loss analysis)

✅ Based on IS 8753:1997 or BS 845 standards.

162. Why is a performance test necessary?

To assess actual efficiency vs design efficiency.

Identify energy losses and improvement areas.

Verify performance after repair or modification.

Support energy audits, benchmarking, and regulatory compliance.

✅ Helps in reducing fuel cost and improving boiler reliability.

163. What parameters are measured during a performance test?

Fuel consumption rate

Steam generation rate

Feedwater temperature

Steam pressure and temperature

Flue gas composition (O₂, CO₂, CO)

Stack temperature

✅ Also includes ambient temperature, humidity, and barometric pressure.

164. What is the indirect method of efficiency calculation?

Determines boiler efficiency by subtracting all heat losses from 100%.

Formula:

Boiler Efficiency (%) = 100 – (L₁ + L₂ + L₃ + L₄ + L₅ + L₆ + L₇)

Where:

L₁ = Dry flue gas loss

L₂ = Moisture loss (fuel + air)

L₃ = Hydrogen combustion loss

L₄ = Unburnt fuel loss

L₅ = Radiation/convection loss

L₆ = Blowdown loss

✅ Gives a complete picture of energy performance.

165. What are the typical efficiency ranges of industrial boilers?

Fire-tube boiler: 75–85%

Water-tube boiler: 80–90%

Condensing boiler: up to 95%

✅ Actual efficiency depends on fuel type, excess air, and heat recovery systems.

166. What causes efficiency deterioration in boilers?

Soot or scale buildup on heating surfaces.

Excess air or air leakage.

High flue gas temperature.

Poor water chemistry or excessive blowdown.

Low load operation for long periods.

✅ Regular cleaning, tuning, and water treatment sustain efficiency.

167. What is the purpose of a boiler heat balance sheet?

Lists heat input and all heat outputs/losses.

Identifies percentage of useful heat utilized for steam generation.

Key tool for energy audits and efficiency monitoring.

✅ Helps pinpoint where maximum energy losses occur.

168. What are the major heat losses in a boiler?

1. Dry flue gas loss

2. Moisture in fuel & air loss

3. Hydrogen combustion loss

4. Unburnt carbon loss

5. Radiation & convection loss

6. Blowdown loss

✅ Reducing these improves boiler efficiency significantly.

169. How can flue gas temperature affect boiler efficiency?

Every 20°C rise in flue gas temperature above design reduces efficiency by ~1%.

Caused by soot deposits, scale, or excess air.

✅ Maintain stack temperature below 200°C for most industrial boilers using economizers.

170. What are economizer losses?

Occur due to fouling or poor heat transfer in economizer tubes.

Caused by soot deposition, low feedwater flow, or corrosion.

✅ Action: Regular soot blowing and maintaining feedwater temperature & flow.

171. What is radiation and convection loss?

Radiation loss: Heat radiated from boiler surface to surroundings.

Convection loss: Heat carried away by air currents.

✅ Controlled by proper insulation, refractory maintenance, and reducing hot surface exposure.

172. How do you determine unburnt carbon loss?

From ash analysis — measures combustible residue in fly ash and bottom ash.

Formula:

Unburnt Carbon Loss (%) = (Unburnt Carbon in Ash × Ash % × GCV of Carbon) / (GCV of Fuel) × 100

✅ Indicates combustion quality — high value means poor air-fuel mixing.

173. What are typical radiation and convection losses?

Modern water-tube boilers: 0.5–2%

Small package boilers: 1.5–3%

✅ Minimized by good insulation, steam jacket design, and minimal exposed surface area.

174. What is the purpose of a boiler efficiency audit?

To analyze fuel-to-steam conversion efficiency.

Detect inefficiencies, leakages, and poor maintenance areas.

Suggest energy-saving measures (economizer, VFDs, condensate recovery).

✅ Conducted annually or semi-annually as part of ISO 50001 energy management.

175. What is the role of an economizer in improving efficiency?

Recovers waste heat from flue gases to preheat feedwater.

Reduces fuel consumption by 5–10%.

Lowers flue gas temperature and increases thermal efficiency.

✅ Common in both fire-tube and water-tube boilers.

176. What is blowdown heat recovery?

System to recover heat from hot blowdown water before disposal.

Used to preheat makeup or feedwater.

Saves energy and water, improving overall efficiency.

✅ Reduces blowdown loss by up to 80%.

177. How do you calculate specific steam consumption (SSC)?

Formula:

SSC = Steam Output (kg/hr) / Fuel Consumption (kg/hr)

✅ Indicates how much steam is produced per kg of fuel — lower SSC means better efficiency.

178. What is the significance of O₂ and CO readings in flue gas?

High O₂: Excess air → heat loss.

High CO: Incomplete combustion → fuel waste.

✅ Optimum values:

O₂: 2–5% (gas/oil)

CO: <100 ppm

Continuous monitoring ensures maximum combustion efficiency.

179. What are the steps in conducting a boiler efficiency test (indirect method)?

1. Measure fuel and steam flow.

2. Analyze flue gas composition (O₂, CO₂, CO).

3. Record flue gas and ambient temperature.

4. Calculate individual losses (dry flue gas, moisture, etc.).

5. Subtract total losses from 100% to get efficiency.

✅ Follow IS 8753 / BS 845 procedure for accuracy.

180. What tools and instruments are used in a boiler performance audit?

Flue gas analyzer (O₂, CO, CO₂, NOx)

Temperature sensors / thermocouples

Orsat apparatus (for manual gas analysis)

Flow meters (fuel, air, steam, and water)

Draft gauge, pressure transmitter, tachometer

✅ Modern audits use portable combustion analyzers and data loggers for precise evaluation.

181. What are the common boiler emissions?

Carbon Dioxide (CO₂): From complete combustion.

Carbon Monoxide (CO): From incomplete combustion.

Nitrogen Oxides (NOx): From high-temperature oxidation of nitrogen.

Sulfur Oxides (SOx): From sulfur in fuel.

Particulate Matter (PM): Unburnt carbon and ash particles.

✅ Emissions depend on fuel quality, combustion control, and load conditions.

182. How is CO₂ emission related to boiler efficiency?

Higher efficiency → less fuel burnt → lower CO₂ emissions.

For every 1% increase in boiler efficiency, CO₂ emissions reduce by about 1.5–2%.

✅ Energy conservation directly supports carbon footprint reduction and sustainability targets.

183. What are the methods to reduce particulate matter (PM) emissions?

Electrostatic Precipitator (ESP): Removes 98–99% of dust.

Bag Filters: Captures fine dust <10 microns.

Cyclone Separator: Removes coarse particles by centrifugal force.

Wet Scrubber: Washes out dust with water spray.

✅ Selection depends on boiler size, dust load, and fuel type.

184. What is a Continuous Emission Monitoring System (CEMS)?

An online monitoring system for real-time tracking of emissions.

Measures SO₂, NOx, CO, CO₂, PM, and O₂ levels in stack gases.

Required under CPCB and SPCB guidelines for pollution control compliance.

✅ Data is transmitted to pollution control boards automatically.

185. What are the benefits of installing a CEMS system?

Ensures regulatory compliance and avoids penalties.

Enables real-time emission control and trend analysis.

Supports ISO 14001 / ESG reporting.

Detects abnormal combustion or equipment malfunction early.

✅ Builds transparency in environmental performance management.

186. What is waste heat recovery (WHR)?

Utilization of heat energy from exhaust gases or process streams that would otherwise be lost.

Used to preheat combustion air, feedwater, or generate additional steam/power.

Equipment: Economizer, Air Preheater, WHR Boiler (HRSG).

✅ Increases overall plant efficiency and reduces fuel costs.

187. What are the main components of a Waste Heat Recovery System (WHRS)?

Heat Source: Flue gases, kiln exhaust, turbine exhaust.

Heat Exchanger: Economizer, air preheater, or HRSG.

Working Medium: Water, air, or thermal oil.

Control System: Regulates flow and temperature.

✅ Converts waste heat into useful energy (steam, hot water, or power).

188. What is a Heat Recovery Steam Generator (HRSG)?

A boiler-type unit that generates steam using exhaust heat from gas turbines or engines.

Works on waste heat recovery principle.

Can be single-pressure or multi-pressure design.

✅ Key component in combined-cycle power plants (CCPP).

189. What are the advantages of waste heat recovery in boilers?

Fuel savings: 10–20% typical.

Reduced emissions: CO₂, NOx, and SO₂.

Improved efficiency and shorter payback.

Smaller boiler size requirement.

✅ Enhances sustainability and meets energy conservation norms.

190. What is a heat pipe economizer?

A compact economizer using sealed heat pipes to transfer heat from flue gas to feedwater.

Provides high efficiency and low gas-side pressure drop.

Suitable for retrofit and low-space applications.

✅ Reduces stack temperature and saves 5–8% energy.

191. What are the key parameters monitored in an energy management system (EMS)?

Fuel consumption (per ton steam or per batch).

Steam generation rate and efficiency.

Stack temperature and O₂ levels.

Condensate recovery and blowdown ratio.

Electrical energy use of auxiliaries (fans, pumps).

✅ Enables continuous performance optimization and benchmarking.

192. What are the objectives of energy management in boiler operations?

Maximize thermal efficiency.

Minimize energy losses and emissions.

Monitor KPIs (Efficiency, SFC, Heat Rate).

Promote preventive maintenance and reliability.

Ensure sustainability and cost reduction.

✅ Aligned with ISO 50001 energy management principles.

193. What is the function of an energy audit in boiler systems?

Identifies energy losses, inefficiencies, and wastage.

Suggests improvement measures like WHR, automation, insulation.

Quantifies fuel savings and CO₂ reduction potential.

✅ Classified as preliminary or detailed energy audit as per BEE standards.

194. What are typical energy-saving measures in a boiler plant?

Optimize combustion with O₂ trim control.

Recover condensate and flash steam.

Install economizer and air preheater.

Use VFDs for fans/pumps.

Automatic blowdown control.

Proper insulation and steam trap maintenance.

✅ Typically saves 10–15% energy.

195. What is a green boiler?

A high-efficiency, low-emission boiler designed for environmental sustainability.

Uses renewable fuels (biogas, biomass) or hybrid systems.

Equipped with condensing economizers and low-NOx burners.

✅ Supports clean energy transition and net-zero carbon goals.

196. What are the key features of a modern green boiler system?

Fully automated controls (PLC/DCS).

O₂ and CO monitoring for efficiency.

Condensing economizer for latent heat recovery.

Renewable or dual-fuel compatibility.

Zero liquid discharge (ZLD) blowdown system.

✅ Combines efficiency, safety, and environmental performance.

197. What is biomass fuel and how is it used in boilers?

Biomass includes agro-waste, wood chips, bagasse, rice husk, or pellets.

Burned in grate or fluidized bed boilers.

Requires proper air distribution and ash handling system.

✅ Renewable and carbon-neutral alternative to fossil fuels.

198. What are the challenges in using biomass as boiler fuel?

High moisture and variable calorific value.

Ash handling and slagging/fouling.

Fuel feeding and storage issues.

Lower energy density compared to coal.

✅ Mitigated by drying, size uniformity, and automation in fuel handling.

199. What is the role of condensate recovery in energy conservation?

Condensate contains ~25–30% of total heat in steam.

Recovery reduces make-up water and fuel requirement.

Minimizes blowdown loss and chemical usage.

✅ 80–90% condensate recovery can save 15–20% fuel energy.

200. What are future trends in boiler energy efficiency and emission control?

Hybrid fuel systems (biogas + natural gas).

Digital twin-based performance monitoring.

AI-driven combustion optimization.

Heat-to-power ORC (Organic Rankine Cycle).

Hydrogen-ready boilers and carbon capture integration.

✅ The future of boilers is smart, digital, and sustainable

201. What is boiler automation?

Boiler automation is the use of control systems (PLC/DCS) to monitor and manage all boiler operations automatically.

Controls fuel flow, air flow, water level, steam pressure, and safety interlocks.

Enhances safety, reliability, and efficiency by reducing operator dependency.

✅ Common systems: CCS (Combustion Control System) and BMS (Burner Management System).

202. What is the function of a DCS (Distributed Control System) in a boiler?

Integrates all field instruments, transmitters, and controllers into one system.

Executes automatic control loops for pressure, temperature, and level.

Records trends, alarms, and event history for analysis.

Communicates with BMS, CCS, and plant SCADA.

✅ Enables centralized monitoring and safe, efficient operation.

203. What is the difference between CCS and BMS?

CCS (Combustion Control System): Controls air, fuel, and load to maintain steady steam output.

BMS (Burner Management System): Manages burner sequencing, ignition, and safety trips.

✅ CCS = Efficiency Control | BMS = Safety Control

Both are interlinked through the DCS or PLC.

204. What is a permissive in boiler control logic?

A permissive is a condition that must be true before an operation (e.g., start) can occur.

Example:

FD fan ON → Draft OK → Fuel valve opens.

✅ Ensures safe sequencing and prevents unsafe startup.

205. What is an interlock in boiler operation?

An interlock automatically stops an operation when unsafe conditions are detected.

Examples:

Low water level → Trip burner.

Flame failure → Shut off fuel supply.

✅ Interlocks protect equipment from damage and prevent accidents.

206. What is the purpose of pre-purge and post-purge logic in BMS?

Pre-Purge: Clears furnace of combustible gases before ignition.

Post-Purge: Clears unburnt gases after flame failure or shutdown.

✅ Ensures no gas accumulation and prevents furnace explosion.

207. What is a boiler trip condition?

A trip is an automatic shutdown of the boiler on unsafe or abnormal conditions such as:

Low water level

High steam pressure

Flame failure

FD/ID fan failure

Safety valve lift

✅ Prevents catastrophic failure or explosion.

208. What is the role of a PID controller in boiler control loops?

Maintains process variables at setpoints using Proportional, Integral, and Derivative actions.

Adjusts control valves for smooth and stable operation.

✅ Example loops: drum level, fuel-air ratio, steam pressure.

209. How do you tune a PID loop in a boiler?

Step 1: Set initial P, I, D = 0.

Step 2: Increase P until oscillations start, then reduce 25%.

Step 3: Add I to eliminate offset.

Step 4: Add D to smooth response.

✅ Auto-tuning functions are often available in modern DCS systems.

210. What are SIL (Safety Integrity Level) systems in boilers?

SIL defines the risk reduction capability of safety systems.

SIL 1–4: Higher level = higher safety integrity.

Applied to Safety Instrumented Systems (SIS) like BMS and emergency shutdown.

✅ SIL ensures quantified reliability of critical safety loops.

211. What are examples of Safety Instrumented Functions (SIF) in boilers?

Low water level trip

High steam pressure trip

Flame failure shutdown

Fuel leak detection trip

Fan interlock trip

✅ Each SIF is validated and tested per IEC 61511 / 61508 standards.

212. What is redundancy in boiler control systems?

Use of backup components to ensure reliability during failure.

Types:

1oo2 (One out of Two) – High reliability.

2oo3 (Two out of Three) – Common for safety-critical sensors.

✅ Prevents spurious trips and improves uptime.

213. What is the difference between hardwired and soft interlocks?

Hardwired Interlock: Implemented via relays or physical wiring; cannot be bypassed easily.

Soft Interlock: Implemented in PLC/DCS logic; can be modified via software.

✅ Hardwired = Safety-critical | Soft = Operational logic.

214. What is an Emergency Shutdown (ESD) system?

A dedicated system that overrides all control logic to bring the boiler to a safe state.

Activated during critical failures (fire, explosion risk, gas leak).

Shuts all fuel valves, fans, and ignition circuits.

✅ Must be tested periodically for reliability.

215. What is an alarm hierarchy in a boiler control system?

High Priority (Red): Requires immediate action (trip, emergency).

Medium Priority (Amber): Needs operator attention.

Low Priority (Blue/Green): Informational or maintenance alerts.

✅ Helps prioritize operator response during abnormal conditions.

216. What is predictive maintenance in boiler systems?

Uses real-time monitoring and data analytics to predict failures before they occur.

Parameters monitored:

Vibration, temperature, pressure, draft, flue gas O₂/CO.

✅ Reduces unplanned downtime and extends equipment life.

217. What sensors are used for predictive maintenance in boilers?

Vibration sensors – for fans, pumps, motors.

Temperature & pressure transmitters – for process monitoring.

Ultrasonic & infrared sensors – for leak and heat loss detection.

Gas analyzers – for combustion health.

✅ Data fed into IoT-based maintenance dashboards.

218. What is the role of data logging and trending in boiler control systems?

Records historical performance data (pressure, temperature, efficiency).

Helps in troubleshooting, optimization, and audits.

Identifies patterns or drift in equipment behavior.

✅ Trending ensures proactive maintenance and regulatory traceability.

219. How can AI (Artificial Intelligence) be applied in boiler operation?

AI-based combustion optimization: Adjusts air-fuel ratio dynamically.

Predictive fault detection: Uses ML to detect early signs of failure.

Efficiency optimization: Real-time tuning based on load conditions.

✅ Leads to autonomous, low-emission, and fuel-efficient operation.

220. What are the benefits of integrating boiler control with plant DCS/SCADA?

Centralized monitoring and control of all plant operations.

Alarm integration for quick fault detection.

Real-time data sharing with ERP/MES systems.

Enables remote monitoring, performance analytics, and reporting.

✅ Results in safer, smarter, and energy-optimized plant operation.

221. What is Root Cause Analysis (RCA) in boiler incidents?

RCA is a systematic method to find the underlying cause of a boiler failure or unsafe event.

Focuses on why an incident occurred, not just what happened.

Steps:

1. Define the problem.

2. Collect data (logs, readings, interviews).

3. Identify contributing and root causes.

4. Develop corrective & preventive actions (CAPA).

✅ Tools: 5 Whys, Fishbone Diagram (Ishikawa), FMEA.

222. What are common root causes of boiler accidents?

Bypassing interlocks or safety valves.

Poor maintenance or inspection frequency.

Operator error or inadequate training.

Defective instruments or calibration failure.

Poor feedwater treatment leading to tube rupture.

✅ Most boiler accidents are preventable through robust training and maintenance.

223. What is SIL verification and why is it important?

SIL (Safety Integrity Level) verification ensures that the safety system achieves the required risk reduction.

Involves analysis of failure probabilities (PFDavg) for all safety components.

✅ Verifies that Safety Instrumented Functions (SIFs) meet IEC 61511 reliability targets.

224. What are the four SIL levels and their target PFD ranges?

SIL Level Probability of Failure on Demand (PFDavg) Typical Application

SIL 1 10⁻² to 10⁻¹ Low-risk protection

SIL 2 10⁻³ to 10⁻² Medium-risk

SIL 3 10⁻⁴ to 10⁻³ High-risk, critical systems

SIL 4 10⁻⁵ to 10⁻⁴ Extremely high integrity

✅ Boilers typically implement SIL 2 or SIL 3 for BMS/Emergency Shutdown systems.  

225. What are Safety Instrumented Functions (SIF) in a boiler system?

Independent safety loops designed to prevent hazardous events.

Examples:

Low water level → Burner trip.

High drum pressure → Fuel valve closure.

Flame failure → Emergency purge.

✅ Each SIF includes sensor, logic solver (PLC), and final element (valve/relay).

226. What is Proof Testing in safety systems?

Periodic testing to confirm that all safety devices perform as intended.

Detects hidden failures in dormant or low-demand systems.

Typical interval: 6 to 12 months depending on SIL level.

✅ Proof testing ensures functional reliability of interlocks and shutdown systems.

227. What is the difference between failure rate and failure probability?

Failure Rate (λ): Number of failures per unit time (e.g., failures/hour).

Failure Probability (PFD): Likelihood that a system will fail when demanded.

✅ PFD = λ × test interval (approximation for low-demand mode).

228. What are the three components of a Safety Instrumented System (SIS)?

1. Sensors – detect abnormal process conditions.

2. Logic Solver (PLC/DCS) – processes signals and initiates trip.

3. Final Elements – valves, relays, dampers performing safety actions.

✅ Designed independently of normal control systems to ensure fail-safe response.

229. What is redundancy management in safety systems?

Use of multiple independent channels for critical measurements or functions.

Types:

1oo2 (One out of Two) – High availability.

2oo3 (Two out of Three) – High integrity, tolerant of one failure.

✅ Reduces spurious trips while maintaining functional safety.

230. What is a Safety Lifecycle?

The structured process for designing, verifying, operating, and maintaining safety systems.

Stages:

1. Hazard analysis & risk assessment.

2. Safety system design (SIL allocation).

3. Implementation, validation, and operation.

4. Modification and decommissioning.

✅ Defined by IEC 61511 / 61508 standards.

231. How do you calculate the Risk Reduction Factor (RRF)?

Formula:

RRF = 1 / PFDavg

✅ Example:

If PFDavg = 0.001 → RRF = 1000 → Equivalent to SIL 3 protection level.

232. What is the purpose of an Alarm Rationalization Study?

Eliminates nuisance or irrelevant alarms to reduce operator overload.

Classifies alarms based on priority, frequency, and consequence.

Ensures that only meaningful alarms demand action.

✅ Conducted per ISA-18.2 or EEMUA-191 standards.

233. What is Management of Change (MOC) in boiler systems?

A formal process for managing design or operational changes safely.

Evaluates the impact on safety, environment, and compliance.

Involves risk review, documentation, and authorization before implementation.

✅ MOC is a key requirement in ISO 45001 and Process Safety Management (PSM).

234. What is Reliability Centered Maintenance (RCM)?

Maintenance strategy focused on preventing failures that impact safety or performance.

Combines preventive, predictive, and condition-based maintenance.

✅ Reduces downtime, optimizes spares, and extends boiler life.

235. What are the main steps of a Root Cause Failure Analysis (RCFA)?

1. Data collection: Event logs, sensor readings, operator interviews.

2. Timeline reconstruction: Sequence of events.

3. Cause identification: Using 5-Why or Fishbone analysis.

4. Validation: Confirm root cause.

5. Corrective action: Implement permanent solution.

✅ Ensures systematic and data-driven problem solving.

236. What is the difference between corrective and preventive action?

Corrective Action: Fixes the root cause after failure.

Preventive Action: Eliminates potential causes before failure occurs.

✅ Both are part of CAPA (Corrective and Preventive Action) management.

237. What is a hazard and operability (HAZOP) study?

A structured review to identify potential hazards and deviations in process design.

Uses guide words like “No,” “More,” “Less,” “Reverse” to challenge design intent.

✅ Ensures that boiler systems are fail-safe and compliant with process safety norms.

238. What are the key performance indicators (KPIs) for boiler reliability?

Boiler availability (%)

Mean Time Between Failures (MTBF)

Mean Time To Repair (MTTR)

Trip frequency

Fuel-to-steam efficiency (%)

✅ KPI tracking helps in benchmarking and reliability improvement.

239. What is the importance of Safety Integrity Verification (SIV) testing?

Confirms that safety systems meet design intent and SIL targets.

Includes loop testing, fail-safe simulation, and logic verification.

✅ Conducted before commissioning and during annual maintenance.

240. What is the difference between functional safety and process safety?

Functional Safety: Focuses on correct operation of safety systems (SIS, interlocks).

Process Safety: Broader scope — ensures containment of hazardous energy or substances.

✅ Functional safety is a subset of process safety, defined by IEC 61511 standards.

241. A worker collapses due to heat stress near the boiler area — what actions will you take?

Move the person to a cool, ventilated area immediately.

Provide cool water, loosen clothing, and monitor breathing.

If unconscious → call emergency medical help immediately.

Report incident to control room and HSE team.

✅ Preventive Measure: Improve ventilation, hydration facilities, and implement heat-stress monitoring.

242. You find expired fire extinguishers near the boiler — what’s your response?

Immediately tag and remove expired extinguishers.

Report to Fire & Safety Department for replacement.

Conduct inspection of all firefighting equipment in the area.

✅ Preventive Measure: Maintain inspection register and ensure monthly checks as per NFPA standards.

243. You notice a worker not wearing PPE near a running boiler — how do you handle it?

Stop the worker immediately from continuing unsafe work.

Counsel and remind about PPE policy.

Report the violation to the supervisor or safety officer.

✅ Corrective Action: Conduct toolbox talks and refresh PPE training.

244. During an audit, missing risk assessment records are found — what will you do?

Inform department head and HSE auditor immediately.

Conduct a fresh risk assessment with proper documentation.

Store records in controlled, retrievable format.

✅ Preventive Step: Maintain a centralized digital HIRA register with version control.

245. A near-miss report was ignored by a supervisor — how would you respond?

Escalate the issue to HSE or management.

Review the incident and classify the risk level.

Conduct a root cause analysis even if no injury occurred.

✅ Culture: Promote a “No blame, safety-first” reporting environment.

246. A contractor is found smoking in a restricted area — what is your response?

Stop the act immediately and remove the person from the area.

Inform the contractor’s supervisor and site security.

Record the violation and initiate disciplinary action.

✅ Preventive Measure: Reinforce no-smoking policy and install clear signage in critical zones.

247. What are typical hazard scenarios in boiler operations?

Overpressure and explosion due to safety valve failure.

Fuel leakage and fire.

Water hammer or tube rupture.

Combustion gas backfire.

Chemical burns from feedwater dosing.

✅ Control via interlocks, alarms, PPE, and regular maintenance.

248. What are common ignition sources in boiler areas?

Sparks from electrical panels.

Static discharge from fuel hoses.

Open flames or hot surfaces.

Faulty wiring or short circuits.

✅ Controlled by intrinsically safe equipment and hot-work permit systems.

249. How do you handle a boiler furnace explosion?

Immediately trip the boiler and isolate fuel supply.

Activate fire suppression and emergency shutdown systems.

Evacuate area and call fire brigade and emergency response team.

After cooling → inspect for damage, root cause, and evidence collection.

✅ Investigation mandatory before restart as per IBR/Factory Act.

250. What are the emergency communication steps in a boiler incident?

1. Inform control room and shift in-charge.

2. Activate plant siren or paging system.

3. Notify fire team and medical services.

4. Inform plant head / HSE / statutory authority if required.

✅ Maintain an updated emergency contact list at all times.

251. What is the importance of a boiler emergency response plan (ERP)?

Ensures structured and immediate action during emergencies.

Defines roles, responsibilities, and communication flow.

Reduces response time and prevents escalation.

✅ Must be tested quarterly through mock drills.

252. What is the “Permit to Work” (PTW) system in boiler maintenance?

A formal authorization to carry out non-routine or hazardous work.

Specifies scope, duration, hazards, and safety measures.

Types: Hot work, confined space, height work, isolation permits.

✅ PTW ensures that maintenance and operation teams coordinate safely.

253. How is “Isolation and Lockout-Tagout (LOTO)” applied in boiler work?

Isolate energy sources (steam, fuel, electrical, pneumatic).

Apply locks and tags to prevent accidental startup.

Verify zero energy state before work.

✅ Part of OSHA and ISO 45001 safe work standards.

254. What are confined space hazards in boiler drums?

Oxygen deficiency, toxic gases, or steam residues.

High temperature and poor visibility.

✅ Control Measures: Gas test before entry, continuous air monitoring, standby person, and confined space permit.

255. What is the emergency procedure for a chemical spill (e.g., boiler water treatment chemicals)?

Evacuate area and wear chemical-resistant PPE.

Contain the spill using neutralizing agents or absorbents.

Dispose waste as per Hazardous Waste Rules.

✅ Maintain MSDS sheets and train personnel on spill management.

256. What key safety systems must always be operational in a boiler?

Safety valves and pressure gauges.

Low water level and flame failure trips.

Purge interlocks and draft control.

Emergency shutdown system (ESD).

✅ Periodic testing and preventive maintenance are mandatory under IBR.

257. How does ISO 45001 apply to boiler operation safety?

Ensures Occupational Health & Safety (OH&S) Management System is implemented.

Requires hazard identification, risk assessment (HIRA), and training.

Integrates incident investigation, MOC, and emergency preparedness.

✅ Aligns boiler operation with legal and regulatory compliance.

258. How does PSM (Process Safety Management) strengthen boiler safety?

Provides structured safety management for high-energy systems.

Covers operating procedures, maintenance, training, and audits.

Includes MOC, incident analysis, and emergency response planning.

✅ Core element in chemical and petrochemical plants for explosion prevention.

259. How often should boiler emergency drills be conducted?

At least once every six months or as required by site HSE policy.

Should simulate real scenarios — fire, explosion, chemical leak, etc.

✅ Evaluate response time, coordination, and communication effectiveness.

260. What are the most critical lessons from past boiler accidents?

Never bypass interlocks or alarms.

Always maintain water level and pressure controls.

Regular inspection, testing, and calibration save lives.

Training, mock drills, and supervision are non-negotiable.

✅ Boiler safety is 90% preventive and 10% reactive — discipline saves both people and plant.