1. a) What is hogging and sagging? Where it is to be seen in the boiler?
Answer: Hogging and sagging describe the shape of a beam or similar long object when loading is applied. Hogging describes a beam that curves upwards in the middle, and sagging describes a beam that curves downwards.
a) Horizontal Tubes
b) Piping between supports
1. b) Which table flange is to be used for w.p. of boiler 30 kg/cm2?
Answer: Table K of Appendix in IBR
1.c) What is the difference between pipe and tubes?
Answer : Pipes: The purpose of a pipe is the transport of a fluid like water, oil, or similar, and the most important property is the capacity or inside diameter.
Tubes: The nominal dimensions of tubes are based on the outside diameter. While the inside diameter of a tube depends on the thickness of the tube.
1.d) Mention types of three lifts provide in the safety valve of boiler?
Answer: Types of three lifts provide in safety valve of boiler •
1. Ordinary lift safety valve
2. High lift safety valve
3. Full lift safety valve
1. e) What are Form-III, Form-lllC, and Form VI?
Form-lll: WORKS ADDRESS CONTRACTOR’S CERTIFICATE OF MANUFACTURER AND TEST ( Regulation 4( c) )
Form-IIIC: CERTIFICATE OF MANUFACTURE AND TEST OF BOILER MOUNTINGS AND FITTING (Regulation 269 )
Form VI: BOILER INSPECTION DEPARTMENT CERTIFICATE FOR USE OF A BOILER ( Regulation 389 )
1. f) What is the difference between IBR boilers and non-IBR boilers?
Answer: Steam boiler as per IBR: It is a pressure vessel in which steam is generated for use external to itself by application of heat which is wholly or partly under pressure when steam is shut off but does not include a pressure vessel.
i) with a capacity less than 25 liters (such capacity measured from the feed check valve to the main steam stop valve)
ii) with less than one kilogram per centimeter square design gauge pressure and working pressure
iii) in which water is heated below one hundred degrees centigrade.
1 .g) Which code is used to design boilers in India and other countries?
India — Indian Boiler Regulation (IBR)- ISO Boiler Code ISO/R-831
US — American Society of Mechanical Engineers ASME Section I
Europe — European Standard for Water Tube Boilers European Norm EN 12952
1. h) At what pressure cast iron is permitted for manufacturing valve and fitting?
Answer: As per Regulation 282 b Cast Iron Valves cannot be used above 13 bar gauge
1. i) Which methods are used for finding efficiency of Boiler?
Answer: There are two methods to find out the efficiency of any Boiler.
Direct Method : Directly calculated through formula.
Indirect Method : Calculated all the losses & get the Efficiency by 100-losses.
1.j) What is the importance of pH value for feed water in a Boiler? How much it should be?
Answer: Desired pH value of feed water is necessary because the higher the pH value protects the boiler from corrosion by creating a magnetite layer. pH value is depending upon the working pressure of the boiler. At about 100bar working pressure, it is about 9.5 to 10.
Q.2(a): What is the constituent in fuel to be considered for chimney height calculation? What is the formula for calculating chimney height?
Sulfur is the constituent in fuel that is considered during chimney height calculation.
Formula for calculating chimney height :
h = 353 H [1/Ta — (w + 1) / wT] mm of water
w = Weight of air required in kg for burning 1 kg of fuel
T = Average absolute temperature of gas passing through the chimney in deg. K
Ta = Absolute temperature of the air outside the chimney in deg. K
h =Furnace Draught in mm of water.
H = Height of chimney in meters
w + 1 = Weight of the flue gas produced in kg per kg of fuel burnt.
Q.2(b): What are the sequential procedures for starting the erection of a new boiler. What kind of load is to be considered for boiler civil foundation. What precautions are to be taken during the civil foundation of the boiler, fans, and chimney.
New Boiler Erection Sequence:
It becomes all the more important for the job site erection group to take utmost care right from the receipt stage to the completion of erection so that commissioning activities can proceed without any difficulties.
The major components in pressure parts to be erected are
1. Boiler Foundation & Civil jobs.
2. Boiler Structures Erection.
3. Boiler drum Erection
4. Headers Erection
5. Water walls and stream cooled walls Erection.
6. Economizer Erection.
7. Air preheater Erection
8. ESP Erection.
9. Stack(Chimney) Erection.
10. Superheater and re-heater coils Erection
11. Buck stays Erection.
12. Hydraulic test to be done.
13. Welding & NDE.
14. Flue gas duct Erections.
15. Auxiliaries & Fans Erection
16. Fuel feeding System Erection
17. Ash disposal system Erection.
18. Chemical dosing system Erection.
BOILER /ESP SUPPORTING STRUCTURE
Boiler/ESP support structure shall be designed for :
1. Dead load
2. Live /imposed loads
3. Static and Dynamic loads for piping rotating equipment etc.
4. Cable trays and walkways are supported on columns.
5. Ash water piping support
6. ESP hopper ash-filled up condition to the extent of top of the hopper
7. To calculate the load the ash density to be taken is 1350 kg/ m3
8. Ash load at the bottom of the hopper and penthouse as specified in the mechanical
9. Wind load and seismic load
10. Temperature load ( +1-25 c ) for atmospheric temperature variations.
11. Temperature load for variation of temperature due to ESP operating conditions,
12. The boiler structure should be so designed that the temperature of the structure should not go beyond 60 deg.
13. Bracing for pipe supports on ESP should be less than 10.0 Mtr height.
14. The plinth level of the Boiler area will be 500mm higher than FGL ( Finished Grade Level).
15. Finished floor level of the boiler area paving shall be kept about 200 mm lower than the
finished floor level of Main Plant buildings.
Boiler/Fans/Chimney/ESP etc. foundation system general requirements are:-
1. Foundations can be open ( isolated footing /raft) or pile foundations depending on the soil
2. The design of foundations should be as per different IS codes.
3. No Major foundations should be on filled-up soil.
4. Open foundations and pile foundations should not be combined in the same structure.
5. Foundations should be designed on a worst combination of loads.
6. For open foundations minimum width is 1.0 M and depth is 1.0M below NGL.
7. Permissible settlement of open foundation of 6.0 M and below span is 40mm
8. Permissible settlement of open foundation of 6.0 M and span(raft) is 75mm
9. Permissible settlement on weathering rock is 12mm.
10. For pile foundations the diameter of the pile shall be 600mm diameter minimum. The vertical compression load will be 140MT. The uplift and lateral load capacity will be 20% and 5% respectively.
11. Initial Pile Load test to be carried out for each diameter.
Vertical (Compression) – 3
Lateral (Horizontal) – 3
Uplift (Tension) – 3
Q3(a) : Your boiler is not able to generate the rated capacity of steam, what are
probable reason and how you will improve the steam generation capacity?
Probable reasons due to boiler unable to generate rated capacity of steam as follows:
1. Stack Temperature is too high (>140*C) — Controlling by effective soot blowing.
2. Economizer inlet feed water temperature is too low(< desired inlet temp). — Controlling by Deaerator charging & Regenerative cycle effectiveness.
3. Combustion air temperature is low due to APH in-efficiency- Controlling by APH periodic inspection, cleaning & corrective measures.
4. Incomplete Combustion of fuel . i.e. higher unburnt carbon loss- Controlling by ensuring complete combustion.
5. Excess air level may be higher —Controlling by maintaining oxygen level in flue gas within the limit.
6. Radiation and Convection Heat Loss is more due to improper insulation.
7. Provision of Automatic Blowdown Control to be made.
8. Tube side scaling due to excessive corrosion. i.e. boiler may be run at higher dissolved oxygen in feed water. Ensure recommended water quality in the boiler.
Q.3(b) : In your economizer tube leakage is suspected, how you will ensure the leakage, and what procedure you will adopt for repair and put it in service after repair?
Ans. There are the following indication when the economizer tube leakage occurs
1 . The tube when got rupture then there is water found in the economizer which can be checked.
2. There are indications and checks by water and steam differences in the boiler.
- Intimate to Boiler inspectorate & take the prior approval to carry out the maintenance
work in economizer coil
-The pinhole was rectified by metal buildup by high-pressure welder.
- The other eroded portion of the tubes were also rectified by metal buildup by high-pressure welder
- A hydraulic test was done and found no leakage from the Economiser tubes
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