Top 60 Boiler Questions and Answers [With PDF]

Today I am going to discuss some Boiler Questions and Answers.

As I have discussed much of boilers in the previous session, If you didn’t go through, then this is the right time to read those boilers functioning, working and more, links are at the end of this session.

Now, let’s dig into the boiler questions and answers quiz and later on you can download this whole Boiler QnA at the end of this session, adding more value to this session.


Q. What is a boiler?

Ans. As the name suggests, Boiler is a closed shell appliance used to generate steam using various fuel mediums.

Q. What is a double boiler?

Ans. The double boiler is a low-pressure, externally fired boiler. It is made of a double boiler shell or pot placed one by one in an upward direction.

Q. How to make a double boiler?

Ans. A double pot is placed under the furnace with water when hot gases are generated through burning fuel, water starts to boil and hence causes generate steam.
Generated steam heat up the next pot.
This double boiler is generally used in the kitchen to melt chocolate and butter and steam cooking items.

Q. How to use a double boiler?

Ans. A double pot is placed one by one in an upward direction pouring water in it and then turning the fuel burner on. This causes the generation of steam into the first shell and this is further released to the second pot placed above the first pot.
This further heated up the food placed in the second pot.
Easy. Isn’t it?

Q. What is a boiler room?

Ans. The boiler room is a mechanical room where various mechanical equipment is stored and operated from there including boilers also.

Q. How long does a boiler last?

Ans. The average age of the boiler is from 11 to 16 years depending on the maintenance and loads on it.

Q. What does a boiler do?

Ans. The boiler is usually used to generate steam to fulfil the mechanical and Electricity purpose.
The best example of boiler usage is – Thermal power plants.

Q. How to turn on the boiler?

Ans. First, you need to check the essential setups and then release the feed pump to feel the required water.
Now, Need to supply the fuel source or electricity to fire up the combustion chamber. Rest is automated.

Q. How much does a boiler cost?

Ans. The average cost of the boiler is from £450 to £3000, depending upon the type and the function of the boiler, you are looking for.

Q. How to clean a water boiler?

Ans. Those green moulds or rust can cause to happen to water boilers with continuous usage.
To get rid of this, this must be clean and to clean, you need the solution of Vinegar-water solution.
First, put vinegar and water in equal amounts and then run the boiler. This will swell the rusting from inside due to the steam formation and thus clean with hand by switching off the boiler.

Q. How to bleed a boiler

Ans. Boiler flushing or boiler bleeding is a process to clean out the boiler inside and break out the jam inside the pipes.
To bleed the boiler, the boiler needs to be at its maximum settings and needs to watch out that when to release the pressure inside generated by turning on the maximum setting of the boiler.

Q. How to drain the boiler?

Ans. The boiler can be drained out by using a Blow-off cock in a conventional boiler.

Q. What is the difference between a boiler and a furnace?

Ans. The basic difference between a boiler and a furnace is working. The furnace is used to supply hot gases or flue gases or heat to the boiler and Otherside the boiler is used to generate the steam.

Q. How does the boiler work?

Ans. The combustion chamber is fired to generate hot gases to heat up the water located inside the tubes. This exchange of heat causes the generation of steam into the boiler and this steam is transferred to further use.
This is the simple and short working of the boiler.

Q. On what factors does boiler thermal expansion depend?

Ans. It depends on the following-
Boiler operating temperature
Boiler tube materials composition
Length of tubes

Q. What are the reasons for the fish mouth failure of boiler tubes/coils?

Ans. Overheating
Erosion & corrosion

Q. What do you mean by priming in boilers?

Ans. It is a carryover of water particles into steam

Q. What could be the probable causes of priming?

Ans. Drum level function
Boiler load fluctuation
Boiler parameters fluctuation

Q. What are the reasons for monitoring oxygen levels in the flue gases?

Ans. To control combustion & achieve maximum efficiency of combustion by optimizing excess air.

Q. What are the functions of the steam drum?

Ans. The steam drum acts as a water storage device
Separates steam & water
Provides space for internal chemical treatment
Removes sludge from boilers through blow dom
Accommodates safety valves to relieve excess pressure during abnormal operating conditions.

Q. What is the function of start-up vents in boilers?

Ans. To control steam pressure during abnormal operating conditions
To increase the main steam temperature during low loads

Q. Why drum dish end thickness is lesser than that of the cylindrical portion?

Ans. Because stress produced in dish ends is circumferential & is less as compared to stress developed in the longitudinal portion.

Q. What is the main reason for the more mainstream temperature?

Ans. More excess air
High moisture fuel
More convective heat transfer at superheater zone due to loss of turbulence
Operating the boiler at lower feedwater temperature at economizer inlet

Q, Why it is not recommended to give blow down during high streaming rates?

Ans. The sudden opening of 180 valves or water wall bottom heater valves will affect circulation rate & may lead to failure of water wall tubes.

Q, What is the function of the draught system?

Ans. To force air into the combustion
To expel out products to combustion from boiler

Q, What are the different types of draughts used in boilers?

Ans. Forced draught
Induced draught
Balanced draught

Q, On what factors does chimney construction depend?

Ans. Quantity of flue gas generated per hour
Draught to be produced
Sulphur content in fuel
Environment clearance

Q, Why boiler is considered a piece of explosive equipment?

Ans. Boiler involves the generation of steam at higher pressure & temperature upon release of this into the atmosphere could cause disaster.

Q. How do you specify the boilers?

Ans. Boilers are specified by their operating pressure, temperature, steam generating capacity & even heating surface.

Q. What are the various circuits involved in boilers?
  • Water circuit
  • Steam circuit
  • Air circuit
  • Flue gas circuit
Q. Why steam is generated at high pressure & temperature?

Ans. High pressure & temperature steam is having more heat content & also has more potential to do work.

Q. What is the standard method or procedure followed for boiler pressure rising during hydraulic tests?

Ans. The pressure rise is 3.5kg/cm2

Q. What will happen, If drum safety valves have been set at higher blow-down rates?

Ans. Superheater coils may overheat due to insufficient flow of steam.

Q. What are the reasons for the failure to superheater coils?
  • Overheating due to insufficient fuel
  • Erosion due to high flue gas
  • Internal scaling
  • Priming
Q. What is the allowable reduction of tube thickness?

Ans. It is around 20% of the original thickness.

Q, Can we feed Raw water directly to the Boiler?

Ans. No, We can not feed raw water directly into the boiler due to impurities present in the water, which will further cause tube failure.

Q. How many types of impurities are present in Raw water?

Ans. There are mainly Four types of impurities present in Raw water-

  • Dissolve Impurities
  • Undissolved Impurities
  • Dissolve gases
  • Other Impurities

Q. How do remove dissolved impurities from water?

Ans. The dissolved impurities are removed by the method of-

  • SAC- Strong Acid Cation
  • SBA- Strong Base Anion
  • MB- Mixed Bed

Q. How dissolved Oxygen is removed from impure water/

Ans. The dissolved oxygen is removed via a deaerator, which is a device to remove dissolved gases from impure water.

Q. Which types of fuel don’t produce Ash content?

Ans. Natural Gas

Q. What is a valve?

Ans. A valve is used to control the flow of fluid inside the pipeline.

Q. What is the difference between hard and soft water?

Ans. Hard water contains excess scale-forming impurities and soft water contains very little or no scale-forming substances.

Q. Which two elements in feed water can cause corrosion of tubes and plates in the boiler?

Ans. Acid and oxygen in feed water lead to corrosion.

Q. What should be done to prevent a safety valve to stick to its seat?

Ans. The safety valve should be blown off periodically so that no corrosion can take place on the valve and valve seat.

Q. What type of boiler does not need a steam drum?

Ans. Super-critical pressure boiler

Q. Why boiler is purged every time before starting firing of fuel?

Ans. Purging ensures that any unburnt fuel in the furnace is removed, otherwise, it may lead to an explosion.

Q. What are the causes of the failure of boiler tubes?

Ans. These are the main causes of boiler tube failure-

  • High thermal Ratings
  • Fatigue cracking due to bending stress

Q. What are the causes of the failure of superheater tubes?

Ans. Failure in superheater tubes may arise from-

  • Prior fabrication history
  • Faulty heat treatment
  • Consequences of welding
  • Overheating of the tube metal
  • Gas-side corrosion
  • Stress corrosion

Q. Why do supercritical boilers use less amount of steel compared to non-supercritical boilers/

Ans. Supercritical boilers do not head heavy drums for the separation of steam from a mixture of water and steam.

Q. Which is economical in operation- Electric heater or heat Pump?

Ans. Heat Pump

Q. Which furnace burns low-ash fusion coal and retains most of the coal ash in the slag?

Ans. Cyclone furnace

Q. How to prevent backfire of boiler?

Ans. keep the boiler furnace always in the negative draft.

Q. What is the functional difference between a gate valve and a sluice valve?

Ans. A gate valve is a positive shut-off valve for liquids and gases and a sluice valve is a non-positive shut-off valve used for heavier materials such as stone, grain, sand etc.

Q. What is HRSG?

Ans. Heat recovery steam generator

Q. What is a fusible plug and why it is used?

Ans. A fusible plug is a device used for the safety of the boiler after a certain temperature, it melts and prevents further increase in the temperature of the boiler.

Q. What is an Economiser?

Ans. An economizer is an accessory of boiler to improve the boiler efficiency.

Q. What is the difference between the air preheater and Air blower?

Ans. Air preheater is used to heat the air required for combustion of fuel in the boiler, whereas an air blower is used to create the necessary draught inside the boiler if natural draught is not sufficient to produce the required pressure difference.

Q. Why baffles are provided in water tube boiler?

Ans. Baffles are provided inside the furnace, it is used to deflect the flame to distribute evenly.

Q. What is the function of a Steam trap?

Ans. To remove the condensate in steam lines.

Q. Why large boilers are water tube types boilers?

Ans. Water tube boilers raise steam fast because of large heat transfer area and positive water circulation. Thus they respond faster to fluctuation in demand.


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