Questions & Answers (Boiler) Part-2

22. Explain why water testing is essential in boiler water management?

1. To prevent scale formation in the boiler & feed water system. 

2. To prevent corrosion in the boiler & feed water system.
3. To control the sludge formation & prevention of carry over with the steam.
4. To prevent entry of foreign matter such as oil, waste, sand copper particles, iron oxide in the boiler.

23. Test carried out on feed water of a low pressure aux boiler: 

Ph Test: 

Reason:
To determine the ph value i.e. the degree of acidity or alkalinity of the water.

Procedure:
· A litmus strip is submerged in the sample water.
· Color of the strip change accordingly to the condition of the water.
· Blue color indicates alkaline & Red means acidic.
· The degree coloration compared against the datasheet to indicate the possible range of ph value.
Alkalinity test:
Reason: To ensure about alkaline condition of the sample.
Test for P-alkalinity:
100 ml of boiler water is taken as a sample.
10 drops of phenolphthalein is added, then sample will twin in pink color.
N/50 sulfuric acid is added to clear the sample.
Calculation: ml of N/50 acid used X 10 = PPM CaCO3.
Test for total alkalinity:

1. P-alkalinity test is taken. 
2. 10 drops of methyl orange is added, result yellow coloration. 
3. N/50 sulfuric acid is added until it turn to pink. 

Calculation: ml of N/50 acid used for both test x 10 = PPM CaCO3.
Chloride test:
Reason: To measure the chloride value to make an indication of sea water leakage in feed water system.
Test:

1. 100 ml of boiler water taken as sample. 
2. 10 drops of phenolphthalein is added sample will turn into pink 
3. N/50 H2SO4 is added to clear the sample. 
4. 2ml of H2SO4 is taken again. 
5. 20 drops of potassium chromate indicator is added. 
6. N/35.5 Silver nitrate solution is added until a brown coloration results.

Calculation: ml of N/35.5 solution used x 10 = P.P.M. Cl.
Phosphate test:
Reason: To determine the amount of phosphate content as a reserve. 

Test:
· 25 ml filtered boiler water is taken as a sample.
· 25 ml vanadomolybdate reagent is added.
· Comparator tube is fitted with this solution z is placed in night hand compartment of the comparator.
· A blank prepared by mixing equal volume of vanadomolybdate reagent and demonized water is placed in left hand compartment
· At least three minutes is allowed to develop the color then compared with disc.

Calculation: Phosphate reserve in P.P.M from the disc reading. 

24. How feed water treatment keeps the boiler scale free?

1) By using distilled water.
2) By keeping the hardness salts in suspension in the solution, to prevent scale formation.
3) By stopping the suspension salt and impurities from sticking on the heat transfer surface.
4) By providing anti foam to prevent water carry over.
5) By eliminating dissolved gases and providing some degree of alkalinity to prevent corrosion.

25.Enumerate the boiler water test

1. Alkalinity test

• a. Phenolphthalein ( p) alkalinity test
• b.Total ( T ) alkalinity test (2 x P)

1. Chloride test
2. Condensate PH test
3. Amerzine test ( Hydrazine test)
4. Excess phosphate test
5. Conductivity test (Total dissolve solids test)
6. Hardness test

26.Purpose of Boiler water test?

1. Alkalinity test:

This is to ensure that the boiler water prevents corrosion by neutralization of acidic gases.
(a) Phenolphthalein ( p) alkalinity
This test is carried out to prevent acidic corrosion.
(b) Total ( T ) alkalinity test
To determine the amount all of hydroxide, all of the carbonate, and two thirds of the phosphates.
Note: Hydroxides and carbonates can co-exist together in a solution but hydroxides
and bi-carbonates can not.
2. Chloride test

1. To know the amount of salt in boiler water.
2. To minimize chloride level and to adjust the blow down.

3.Condensate PH test

1. To control condensate PH value within a limit. 
2. To minimize corrosion in steam and condensate system.

4. Amerzine test ( Hydrazine test)

1. To test for dissolved Oxygen content ****
2. To know reserve hydrazine (N2H4) ppm and to prevent corrosion and aeration.
3. To minimize oxygen pitting and corrosion in boiler, steam and condensate system.

5. Phosphate test

1. To control the scale formation due to hardness (presence of Phosphate in sample means no hardness salts).
2. A reserve of phosphate should be maintained in the boiler water ready to neutralize any hardness salts which may enter.

6. Conductivity test

1. Measure of the total amount of dissolved solids (T.D.S) including the treatment chemicals. (Excessive density leads to priming and or deposits)
2. To remove dissolved and suspended solid by blowing down.

7. Hardness test

1. To check for salt causing "hardness"
2. Hardness test of boiler water are not necessary when the phosphate is above the lower limit of the control range.

27. Describe the correct procedure of blowing down boiler water (partial blow down).

Blowing down procedure of boiler (partial blow down)

1. Put notice
2. Take permission from the port authority if the ship at port.
3. At first close all the steam requirement v/v to purifier, F.O tanks etc.
4. Wear proper clothing.
5. Blow down the gauge glass by taking feed water in the boiler.
6. Stop the water p/p and keep it to normal mode.
7. Maintain sufficient pressure in the boiler.
8. Stop firing of the boiler.
9. Cutoff the F.O system of the boiler.
10. Keep one person standby near the gauge glass.
11. Ensure that the ship side v/v outside of the ship nobody is working or no fishing boat is there.
12. First open the ship side v/v fully.
13. Remove the scum by scumming.
14. Finally crack open the boiler blow down v/v to avoid thermal shock & water hammering.
15. Keep eye on gauge glass.
16. Close the blow down v/v & then ship side v/v before low water level of the boiler.

28. Significance of regular blow down:

1) To reduce the water level in the boiler to prevent carry over or priming.
2) To reduce corrosion.
3) To remove sludge or mud from the boiler.
4) To reduce solid particles.
5) To reduce the dissolved solid.
6) To reduce oil by scum blow down.
7) To reduce chloride.

29. What is foaming in boiler and how to prevent it ?

It is the formation of thick layer of steam bubbles on the top of the water surface inside the boiler due to:

1. High concentration of impurities.
2. By the animal or vegetable fats in feed water carryover from the oil heaters.
3. Increase in level of dissolved & suspended solid TDS level.
4. Increase in water level.

To prevent foaming , surface or scum blow down should done frequently to expel any floating impurities for the boiler and no lube oil should be allowed to enter the boiler.

30. What is boiler priming and how to prevent it ? 

It is condition in which large amount of water are carried along with the steam into the steam line.
It is caused by:

1. Excessive foaming 

2. Improper amount of steam space 

3. By a sudden rush of steam such as is produced when steam stop valve is suddenly opened.
To prevent priming: 

1. Never keep the water level too high.
2. Open steam stop valve slowly.

31. Why are boiler manholes elliptical in shape?

The boiler manhole-lids are mounted from the inside of the boiler so that the boiler pressure will help to keep them tight. Hence the manholes have to be elliptical in shape to make it possible to take the lid out from the boiler.

32. Describe the procedure followed to raise steam from a cold boiler.

Procedure to raise steam from a cold boiler:

1)            Wear proper clothing.

2)            Ensure all piping involving water; steam and fuel are in order.

3)            Make sure that uptake cover is removed safety v/vs are in order.

4)            Ensure boiler plant in operational order.

5)            Shut main steam stop v/v.

6)            Take water to the boiler at 1/4 rd of the gauge glass.

7)            Blow down the gauge glass to check it.

8)            Check the F. O. tank temp & system.

9)            Make sure that air vent of steam drum and super heaters are open.

10)          Start the blower to make the combustion chamber gas free.

11)          Start the boiler F.O. circulating p/p/ booster p/p.

12)          Inject the fuel and light up the burner.

13)          According to the manufacturer warm up the boiler by continue firing for 5 minutes every half an hour.

14)          Take personal safety from back fire.

15)          Shut the vent of steam drum when white steam come out.

16)          Ensure the sufficient quantity of water is available in boiler.

17)          Take normally 18-24 hours for complete operation.

18)          Thus the boiler is ready for work.

32. What action will you take in case of foaming and priming?

1. Scum blow down.

2. Reduce boiler fire rate.

3. Check whether boiler chemicals added are in excess.

4. Detect the source of contamination.

5. In case of bad priming the boiler may have to be taken out of service, shut down.

6. For contamination due to oil have to be chemically cleaned.

33. Boiler blow down procedure ( cool down):

1. Change the fuel oil burning system from HO to DO and then shut down the burning system.
2. Stop feed pump close feed check valve.
3. Drain down the boiler after allowing it to cool down.
4. If no sufficient time to do this, lower the boiler pressure to 3 to 4 bar.
5. Shut the main steam stop valve.
6. Open the ship side valve then open the blow down valve.
7. Banging noise will appear when boiler is empty.
8. Close the boiler blow down valve and ship side valve.
9. Then release the steam pressure through safety vlv by means of easing gear.
10. When pressure is off, open the air vent and the boiler to cool down.

34.Describe the maintenance procedure of a cascade tank.

Maintenance procedure of cascade:

1. Changing the filter periodically which protects the boiler system from any                   contamination.
2. Maintaining the cascade tank water level.
3. Maintain the water temp. around 600C.
4. Maintaining the correct operation of flat v/v.
5. Keeping clean the tank and sight glass.
6. Always supply clean drain return to the cascade tank.
7. Always drain the tank for scum out.
8. Tank should be covered to prevent entry of any dirt or foreign matters.
9. Tank surface should be scale and deposit free.

35. Prevention of oxidation: 

Oxidation which is responsible for metal corrosion can be prevented by preventing any ingress of dissolved oxygen.
This can be done by two ways.

1. Mechanically 
2. Chemically. 

• Mechanically it is done by de-aerating equipment. 
• Chemically add chemical to boiler water such as sodium sulphite or hydrazine. 2Na2SO3+O2 = 2Na2SO4 

        N2H4 + O2 = 2H2O + N2

36. Prevention of acid corrosion: 

Acid corrosion occurs due to magnesium chloride & carbon dioxide with continuous supply of dissolved oxygen (MgCl2, CO2) in the boiler water.

• This can be prevented by lime (Ca(OH)2) and soda ash (Na2CO3) & scavenging the oxygen. 

MgCl2 + Ca(OH)2 = Mg(OH)2+CaCl2 

CaCl2 + Na2CO3 = CaCO3 + 2NaCl

37. Opening up and Inspection Procedure

After making sure no vacuum in it, Then---
1. To remove top man hole door, slacken the dog holding nuts but do not remove them until first broken the joint.
2. Remove nuts and dogs and take out the door.
3. The bottom door can be removed after warning personnel to keep clear of the top door.
4. Make ventilation before entering. Do not allow naked light near the boiler.
5. Preliminary internal inspection carried out before cleaning, to check scale deposits and any special points.
6. Plug orifice to blow down valve to prevent choke, place guards over the manholes landings to prevent damage.
7. Carried out cleaning and internal works.
When all works completed, a full internal examination must be carried out:

1. Cleanliness, all openings are clear, water level gauge connection clears from deposits.
2. All internal pipes and fittings have been replaced correctly and securely attached.
3. Remove plug from the blow down valve orifice.
4. The face of manhole doors and landings inspect to clean and undamaged).
5. Replace manhole doors by using new joints.
6. Operate all boiler mountings. Open air vent cock and fill the boiler with water to sufficient level.

38. How external and internal treatment of boiler feed helps to reduce the scale formation inside the boiler? 

Scale is formed inside the boiler due to presence of salts in the feed water. This scale formation can be reduced by reducing the content of salt. 

This is achieved externally by:
- Using evaporated fresh water or evaporated sea water.
- Proper filtering of feed water.
- Maintaining the correct feed temp.
- De-aeration.
Internally this is done by:
- Ensuring a chemicals reserve dissolved in the feed water in the boiler.

39. How do take action if gauge glass showing low water level?

If water level has not yet dropped completely out the sight glass, water may be put into the boiler.
If water drops completely out of sight glass, check another sight glass, if both disappear water; do not add water until the boiler is cool enough to prevent any possible damage due to rapid cooling of over heated plate.
1. The fire must be immediately stopped.
2. The main steam stop valve must be closed.
3. Blow down and cool down the boiler.
4. Check leakage, drum outside, Located the cause of trouble and make necessary repair.
5. Enter the boiler after it has cooled and examined any possible damage.
6. After repair, water fill up slowly and restore to normal operation.
7. If no damage occurred, inject the water slowly into the boiler and restore it to operation.

40. What are the possible causes if gauge glass shows no water?

1. One gauge glass defective.
2. Boiler tube crack and leaking.
3. Feed regulator jammed.
4. Fail feed pump (Air in feed water line or pump).
5. Level controller malfunction.
6. Steam consumption is too much.

References: 

1. Marine Engineers' World (Facebook)

2. Bangladesh Marine Academy 

3. Hand Notes of Mr. Min Zar Tar

4. Manual Book: AALBORG MISSION OM 1200

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