Top-70 Questions and answers for boiler operators viva exam.

Viva questions and answers for Boiler operators

1.What are the various types of valves used in Boilers?

Globe valve, Gate valve, Butterfly Valve, Diaphragm valve, needle valve, solenoid valve, control valves, safety valve etc

2.What is the function of gate valve?

Gate valve is used to isolate the flow completely

3.What is the function of Globe valve?

Globe valve is used to regulate the flow, it is used for fine controlling of flow.

4.How do you identify the gate and globe valves by just physical observation?

All rising spindle valves are gate valve and non-rising spindles are globe valves. In gate valve operating wheel remains on the same position and spindle rises up and down.

In Globe valve operating wheel rises up and down along with spindle.

5. What are the different classes of valves?

Valve classes: #150, #300, #600, #800, #900,#1500 and #2500

6. What is meant by valve class?

Valve class indicates the pressure-temperature rating of a valve as per standards like ASME. It defines the maximum pressure the valve can withstand at a specified temperature.

7. Why are higher class valves used in boilers?

Higher class valves are used because boilers operate at high pressure and temperature. These valves can safely withstand severe operating conditions.

8. Which valve class is generally used for superheated steam?

Class 600, 900, 1500 & 2500 or higher valves are generally used for superheated steam applications.

9. Why are gate valves preferred in steam lines?

Gate valves provide minimum pressure drop and are suitable for fully open or fully closed service.

10.What you will do if Silica level in drum increases more than recommended limit?

Initially operate the CBD valve, if not controlled give IBD at every one hour for 30 sec to 60 sec.

11.What will happen if pH of feed water decreases below 7

Operating the Boiler at pH < 7 will lead to failure of pressure parts

12.Why are boiler water parameters important?

They are important to:

• Prevent scale formation
• Avoid corrosion
• Improve boiler efficiency
• Protect boiler tubes
• Ensure safe operation

13. What is TDS in boiler water?

TDS means Total Dissolved Solids present in boiler water.

14. Why should TDS be controlled?

High TDS causes:

• Foaming
• Carryover
• Scaling
• Poor steam quality

15. What is boiler blowdown?

Blowdown is the process of removing concentrated water from the boiler to control TDS and sludge.

16. What is hardness in water?

Hardness is caused mainly by calcium and magnesium salts present in water.

17. What is the ideal hardness of boiler feed water?

Ideally, hardness should be zero or nearly zero.

18. Why is dissolved oxygen dangerous?

It causes corrosion and pitting in boiler tubes and pipelines.

19. How is dissolved oxygen removed?

By:

• Deaerator
• Oxygen scavenger chemicals like Hydrazine or sodium sulphite

20. What is conductivity in boiler water?

Conductivity indicates the ability of water to conduct electricity due to dissolved salts.

21. What is phosphate treatment?

Phosphate chemicals are added to prevent scale formation by converting hardness salts into soft sludge.

22. What happens if boiler water pH becomes too high?

Very high pH can cause caustic embrittlement and foaming.

23. What are the effects of poor boiler water quality?

 Tube failure

 Corrosion

 Scaling

 Reduced efficiency

 Steam contamination

 Boiler explosion risk

24. What is combustion?

Combustion is the chemical process of burning fuel in the presence of oxygen to produce heat.

25. What are the basic requirements for combustion?

The three basic requirements are:

• Fuel
• Oxygen (air)
• Heat (ignition source)

This is called the fire triangle.

26. What is complete combustion?

Complete combustion occurs when fuel burns fully with sufficient oxygen, producing maximum heat with minimum smoke.

27. What are the products of complete combustion?

Main products are:

• Carbon dioxide (CO₂)
• Water vapor
• Heat

28. What is incomplete combustion?

Incomplete combustion occurs when insufficient air is supplied to fuel.

29. What are the effects of incomplete combustion?

 Smoke formation

 Carbon monoxide production

 Fuel wastage

 Low efficiency

 Soot formation

30. Which gas indicates incomplete combustion?

Carbon monoxide (CO).

31. What is excess air?

Excess air is the additional air supplied beyond theoretical air for complete combustion.

32. What happens if excess air is too high?

• Heat loss increases
• Boiler efficiency decreases
• Fuel consumption increases

33. What is atomization?

Atomization is breaking liquid fuel into fine droplets for better combustion.

34. What colour indicates good combustion flame?

Blue or light yellow flame generally indicates good combustion.

35. What does black smoke indicate?

Black smoke indicates incomplete combustion and insufficient air.

36. What are the types of draft?

 Natural draft

 Forced draft

 Induced draft

 Balanced draft

37. How can combustion efficiency be improved?

 Proper air-fuel ratio

 Good atomization

 Clean burners

 Proper draft control

 Regular maintenance

38. What happens if furnace pressure becomes positive?

Flames and hot gases may come out from openings, creating unsafe conditions.

39. What is spontaneous combustion?

Self-ignition of fuel without external flame due to heat buildup.

40. What is a boiler hydraulic test?

A hydraulic test is a pressure test conducted on a boiler using water to check the strength and leak tightness of boiler parts.

41. Why is hydraulic testing done in boilers?

Hydraulic testing is done to:

• Check leakage
• Verify strength of pressure parts
• Ensure safe operation
• Detect weak portions or defects

42. Why is water used in hydraulic testing instead of air?

Water is nearly incompressible and safer than air. If failure occurs, stored energy is less, reducing accident risk.

43. What is the usual hydraulic test pressure?

The hydraulic test pressure is generally 1.5 times the working pressure of the boiler.

44. Why should air be removed before testing?

Entrapped air can compress and create dangerous pressure surges.

45. What is checked during hydraulic testing?

 Leakage

 Pressure drop

 Cracks

 Sweating at joints

 Deformation

45. What defects can hydraulic testing reveal?

 Cracks

 Weak welds

 Porosity

 Leakage

 Defective joints

46. What is steam blowing?

Steam blowing is the process of cleaning steam pipelines using high-velocity steam to remove rust, welding slag, dust, and foreign particles.

47. Why is steam blowing carried out?

Steam blowing is done to:

• Clean steam lines
• Protect turbine blades and valves
• Remove construction debris
• Ensure safe operation

48. When is steam blowing performed?
Steam blowing is generally performed:

• Before commissioning a new boiler
• After major shutdowns
• After replacement of steam piping

49. What is the principle of steam blowing?

High-velocity steam creates sufficient force to dislodge and carry away debris from pipelines.

50. What is a target plate in steam blowing?

A target plate is a metal plate placed in the steam path to check cleanliness of steam.

51. What material is commonly used for target plates?

Polished stainless steel or aluminum plates.

52. What are common boiler problems associated during operation?

Common problems include:

• Low steam pressure
• High fuel consumption
• Flame failure
• Tube leakage
• High stack temperature
• Low water level
• Excess smoke

53. What causes low steam pressure?

Possible causes:

• Low firing rate
• High steam demand
• Poor combustion
• Fuel shortage
• Tube scaling

54. What causes high fuel consumption?

 Poor combustion

 Excess air

 Soot deposits

 Steam leakage

 Improper burner settings

55. What causes black smoke from boiler chimney?

Black smoke indicates incomplete combustion due to insufficient air.

56. What causes white smoke from chimney?

White smoke may indicate:

• Excess moisture
• Cold furnace
• Steam or water carryover

57. What causes flame failure in a boiler?

 Fuel supply interruption

 Low atomizing pressure

 Ignition failure

 Improper air-fuel ratio

 Faulty flame scanner

58. Why is furnace purging necessary?

To remove unburnt fuel gases and prevent furnace explosion.

59. What causes low water level in boiler?

It may overheat boiler tubes and cause tube bursting or explosion.

60. What causes high water level in boiler drum?

 Excess feed water

 Faulty feed control valve

 Swelling due to load changes

61. What causes boiler tube leakage?

 Corrosion

 Overheating

  Scaling

 Erosion

 Poor water quality

62. What should be done if tube leakage occurs?

Reduce load or shut down boiler safely for repair.

63. What causes high stack temperature?

 Soot deposits

 Dirty economizer

 Excess air

 Poor heat transfer

64. What are causes of boiler vibration?

 Improper combustion

 Fan imbalance

 Loose mountings

 Water hammer

65. What causes safety valve lifting frequently?

 Excess pressure

 Faulty pressure control

 Improper valve setting

66. What causes boiler corrosion?

Oxygen, Low pH and Poor water treatment

67. Why should boiler logbooks be maintained?

For monitoring performance, troubleshooting, and future reference.

68.Which safety valve will pop up during overpressure?

Super heater safety valve

69.What is the function of Start up vent valve?

To ensure minimum steam flow from super heaters to avoid over heating of the coils.

70.What is the MOC of evaporator, economiser and super heater coils?

Evaporator & Economiser coils: Carbon steel

Super heater : Alloy steel