Boiler

Boiler accumulation pressure test

Boiler water Treatment

Limit of values of tests:-

Tests	Smoke tube boiler Up to 18 Bar	Water tube boiler Up to 18 Bar	Water tube boiler 18-64Bar
Alkalinity (PPM as CaCO3)	300-500	150-300	50-100
Chloride (Max PPM as NaCl)	150-400	75-200	40-60
Dissolved solids conductivity at 25 deg cel. (Max) µs/cm	4500	2250	600
EDTA(Ethylene Diamine Tetra Acetic acid) Hardness (PPM as CaCO3)	5	5	1
Sulphite excess (PPM as Na2SO3)	50-100	50-100	70-50
Phosphate reserve (PPM as Na2SO3)	30-70	30-70	30-50
Hydrazine Reserve (PPM as N2H4)	30-70	30-70	0.1-1.0
P.H	8.3-8.6	8.3-8.6	8.3-8.6

Test procedures:-

1. Test for alkalinity:-

[A]. Phenolphthalein Alkalinity test:-

a. Take 100ml of boiler water.

b. Add 10 drops of phenolphthalein.

c. Titrate with (N/50) H2SO4, so as to clear the sample.

d. PPM of CaCO3 equivalent=ml of (N/50)H2SO4 X 10.

[B]. Total Alkalinity Test:-

a. Continue with the same sample.

b. Add 10 drops of methyl orange.

c. Titrate with (N/50)H2SO4 with colour becomes pale pink.

d. PPM equivalent of T-alkalinity= ml of (N/50)H2SO4 used in both test X10.

[C]. Caustic alkalinity test:-

a. Take 100ml of boiler water sample and add 10ml of Barium chloride. Add 10drops of phenolphthalein.

b. Titrate with (N/50) sulphuric acid to clear the sample.

c. PPM of CaCO3 = ml of (N/50)H2SO4 X10

2. Chloride test:-

a. Continue with the sample of phenolphthalein alkalinity test

b. Add 2ml of H2SO4, add 20 drops of potassium chromate indicator.

c. Titrate with (N/35.5) silver nitrate solution until a brown colour appears.

d. PPM of CaCO3 equivalent of chlorides = ml of (N/35.5) silver nitrate solution X 10

3. TDS test:-

a. This test indicates the density of boiler water.

b. It is the quantity of TDS per unit volume or mass of the water.

c. The density of boiler water should be maintained low.

d. High density boiler water results in precipitation and scale formation.

e. Test can be done by using (i) Hydrometer (ii) Conductivity meter.

(i) Hydrometer Test:- When the hydrometer is allowed to float in a solution of common salt or S.W at 93 deg. cel. the hydrometer reading is taken as 1/32 or relative density of 1.025 or 1025gm/litre. In the pure distilled water the hydrometer read zero corresponding to 1000gm/litre in the metric scale. A sample of boiler water is taken and cooled. Hydrometer is allowed to float & reading of density noted.

(ii) Conductivity meter:- Collect the boiler water sample and cool it around 15 to 25 deg cel. Add two drops of phenolphthalein indicator and remove the pink colouration with acid. Wash the conductivity cell and fill it with the treated sample of boiler water. Plug the filled cell to the conductivity meter Operate the central control unit null balance of the electrical bridge circuit is achieved. position of the central control indicates the T.D.S in micro mhos. For conversion in PPM TDS = Conductivity in micro mhos X 0.7

4. Hardness test:-

a. Take 100ml of boiler water sample.

b. Add 2ml of ammonia buffer solution.

c. Add 0.2gm of mordant black-11 indicator & stir well. If hardness salts are present, the solution turns wire red.

d. Titrate with EDTA solution until colour change to purple and then blue. PPM of CaCO3 = ml of EDTA solution used X 10 e. Reason for colour change:- EDTA neutralises the hardness causing salts, then reacts with the indicator to show the change of colour. the amount of EDTA used gives a measure of hardness causing salts.

5. Sulphite test:-

a. This test is conducted to determine the sulphite reserve in the boiler water to tackle the small quantities of dissolved oxygen.

b. Take 100ml of boiler water sample.

c. Add 2ml of sulphuric acid.

d. Add 1ml of Starch solution and nitrate with potassium Iodideiodate solution. until the sample turns blue.

e. ml of Iodideiodate solution used X 12.5 = PPM of Na2SO3 in sample

6. phosphate test:-

a. Take 25ml of filtered sample of boiler water.

b. Add 25ml of vanadomolybdate reagent.

c. Fill the comparator tube with this solution and place it is the right hand compartment of the comparator. In the left hand compartment place a standard reference by mixing equal volumes of vanadomolybdate reagent and distillate water.

d. Allow the colour to develop for at least 3 minutes and compare with the disc comparator the disc reading gives the phosphate reserve in PPM.

7. Hydrazine test:-

a. Test Immediately upon drawing water sample. Fill comparator test tube with sample up to 5ml.

b. Add 5ml amerzine reagent, place the stopper of test tube and mix well.

c. Place in the test tube in comparator block, allow to stand 3 minutes.

d. Compare the colour with standard Hydrazine comparator block.

8. P.H Test:-

Litmus paper test:- Used to ascertain the degree of acidity or alkalinity of thee boiler water. Insert a litmus paper into the sample of boiler water. The litmus paper change its colour to blue when sample is alkaline and red when water is acidic.

Burners

Burners are classified depending on the way fuel is atomized for combustion. They are classified as:

a. Pressure jet fuel oil burner.

b. Rotary cup fuel oil burner.

c. Steam blast jet type fuel oil burner.

The ratio of the maximum to minimum oil throughput of the burner is known as the turn down ratio of the burner, and in the case of pressure jet burners this can be stated in terms of the square root of the ratio of the maximum to minimum oil supply pressures.

Pressure Jet fuel oil burner

Pressure Jet fuel oil burner consists of a burner barrel, which is attached to swirl and orifice plates. The assembly is held in place by a cap nut. The unit is clamped into a burner carrier that is attached to a boiler casing. The pressurised fuel oil is supplied to the burner. As the oil passes through angled holes in the swirl plate, rotational energy is imparted. The rotating oil stream is forced through a small hole in the orifice plate. This causes the fuel Jet to break up into fine droplets. A fine hollow rotating cone of oil leaves the burner. A pressure jet oil burner. Forms a simple robust unit, widely used in marine boilers. The basic assembly consists of a steel tube, or barrel, to which are attached swirl and orifice plates; these are made of a high grade or low alloy steel, and are held in place by a cap nut. The complete unit is clamped into a burner carrier attached to the boiler casing. This holds the burner in its correct position relative to the furnace, and also permits the supply of fuel through an oil tight connection. Some form of safety device must be fitted in order to prevent the oil being turned on when the burner is not in place. The oil is supplied to the burner under pressure and, as it passes through, the burner performs two basic operations. First it imparts rotational energy to the oil as it passes through angled holes in the swirl plate. The rotating stream of oil thus formed is then forced under pressure through a small hole in the orifice plate which causes the jet to break up into fine droplets. This latter process is referred to as atomization, although each individual droplet of oil is formed of vast numbers of atoms. As the final result of these operations a hollow rotating cone, formed of fine particles of oil, leaves the burner tip. Many variations of design exist for the swirl and orifice plates. In this type of burner control over the throughput of oil is obtained in two ways; by varying the oil supply pressure and/or by changing the diameter of the hole in the orifice plate. Limitations exist which prevent either method being used as the sole means of control over a wide range of throughput. In all pressure jet burners, however, a minimum supply pressure in the order of 700 KN/m2 is necessary to ensure efficient atomization is maintained. At the same time various practical considerations limit the maximum pressure to about 7000 kN/m2, thus the turn down ratio with this type of burner is limited to a value of about 3.5. If a wider range of turn down is required a system incorporating a number of burners is used, which controls the overall turn down on the basis of the number of burners in operation, or changing the orifice size in addition to the variation in supply pressure considered above. However, while this system is convenient for manual operation, it is not suitable for automatic control due to the need to change orifice sizes when the oil supply pressure reaches its upper or lower limits. The burners must be kept clean and care should be taken during this operation not to damage or scratch the finely machined surfaces of the swirl and orifice plates. The latter should be renewed as the orifice wears beyond a certain amount. This should be checked at regular intervals by means of a gauge. After cleaning make sure all the various parts are correctly assembled. Any oil leaks must be rectified as soon as possible as they can lead to fires in the air register or double casing of the boiler. Burners not in use should be removed, otherwise the heat from the furnace will cause any oil remaining in the burner barrel to carbonize.

Rotating cup type of fuel oil burner.

Rotary cup burner supplies rotational energy to the oil and atomises oil by breaking it into fine particles. A hollow cone of fine oil droplets are formed at the burner tip. A V belt connected to an electric motor drives the rotary cup shaft of the burner. The cup is attached to the rotating shaft mounted on ball or roller bearings and rotated at 5000 rpm. Fuel oil is supplied to inner surfaces of the cup, through the hollow end of the spindle. Due to high rotational speed, the centrifugal force causes the fuel to spread out evenly into a thin film. The fuel then moves along the taper to the end of cup. As it passes into the surrounding air stream, the fuel is atomised and broken into very fine droplets. Rotary cup burner does not require high fuel supply pressure as in pressure jet burner. Hence, it can be used with gravity type fuel oil supply system. A rotating cup oil burner atomizes the oil by throwing it off the edge of a tapered cup being rotated at high speeds of between 2000-7000 rpm by either an air turbine driven by primary combustion air, or by an electric motor driving the cup shaft by means of vee belts. The basic assembly, consists of a tapered cup fitted onto the end of a central rotating spindle mounted on ball or roller bearings. The fuel oil is supplied to the inner surface of the cup through the hollow end of the spindle. Here centrifugal force causes it to spread out evenly into a thin film, which then moves out along the taper until it reaches the lip of the cup, where the radial components of velocity cause it to break up into fine particles as it passes into the surrounding air stream. Thus like a pressure jet burner this type of burner performs two functions: first, supplying rotational energy to the oil. and then breaking it up into fine particles. The final result is a hollow rotating cone of oil droplets leaving the burner. High oil supply pressure is unnecessary as this pressure plays no direct part in the atomization process, and only sufficient pressure to overcome frictional resistance to the flow of oil through the pipes is required. Thus this type of burner can be used with a gravity type oil fuel supply system. The oil throughput is controlled by a regulating valve placed in the fuel supply line, and thus can easily be adapted to automatic control. Here the wide turn down ratio available with this type of burner is a great advantage. Values of over 10:1 are possible. The diameter of the cup must be large enough to handle the required throughput, and there must be sufficient taper and rotational speed to ensure the oil is thrown off with the desired velocity. These factors govern the maximum oil throughput of the burner; the minimum throughput is limited only by the fact that sufficient oil must be supplied to maintain a continuous film of oil inside the cup so at to provide a stable primary flame. The flame produced by a rotating cup burner tends to be long and cigar shaped, although a shorter flame can be obtained by careful design of the swirl vanes in the air register, so as to direct the flow of air in such a manner as to give the desired flame shape. In the smaller units it is possible to supply all the combustion air through the burner itself, the air flowing through the space between the rotating cup and the fixed casing. However, in most cases only the primary air, which in this type of burner is used mainly for atomization, is supplied in this way. It only forms about 10 per cent of the total air required, the remainder being delivered through a secondary air register, to which it passes by means of a separate air duct with its own forced draught fan. This type of burner is difficult to design for very large throughputs, and still give the required flame shape, and so while very suitable for auxiliary boilers with their relatively small outputs, they are not in general use for main water tube boilers. Here if more than one burner is to be fitted, the complication inherent in each rotating cup burner, with its own drive motor, makes other systems of atomization more suitable. Also rotating cup burners cannot be used in roof fired boilers.

Steam blast jet type fuel oil burner.

With automated control systems it is advisable to avoid extinguishing and re-igniting burners while manoeuvring, etc. It is also impracticable to change the size of the atomizing tip automatically. Thus simple pressure jet burners with their limited turn down ratios on a single orifice size are not suitable, since it is necessary to use a type of fuel oil burner with a large turn down ratio. Various forms of these wide range burners are available, and one type in common use is the blast jet burner. These atomize the oil by spraying it into the path of a high velocity jet of steam or air. Although either medium can be used, steam is usually both more readily available and economical at sea. Compressed air is therefore seldom used, except when lighting up from cold. In this the steam flows along the central passage, and is then expanded through a convergent divergent nozzle. where its pressure energy is converted to kinetic energy resulting in a high velocity jet of steam. Oil sprayed into this jet is entrained by it being torn to shreds and atomized in the process. The exit ports are arranged tangentially, thus giving the necessary swirl to the oil droplets in order to form the hollow rotating cone of fine particles of oil needed for the efficient combustion of a residual fuel oil in the boiler furnace. However, the flame shape is not so clearly defined as those obtained with pressure jet type burners due to the entrainment of air by the high velocity steam. This enables simple air registers to be used. There is no need to fit the usual swirl vanes for the secondary air stream - only a ventury shaped throat and tip plate are required. The throughput of oil is controlled by varying the oil supply pressure. Since the atomizing effect is not obtained directly by the use of pressure, the same limit is not imposed on the use of very low oil supply pressures as with simple pressure jet burners; large turn down ratios of up to 20:1 are therefore available with blast jet burners without having to resort to unduly high pressures. The oil supply pressure ranges from about 140-2000 kN/m2, with corresponding steam pressures of 140-1500 kN/m2. Care must be taken to use only dry steam, any water present having a chilling effect which could cause flame instability. The steam may be obtained directly from the boiler, the pressure being dropped to the required value by passing it through reducing valves. Alternatively it may be obtained from an auxiliary source such as a steam to steam generator. Excessive use of steam can be caused by incorrect setting of the burner, or by leakage across the joint faces in the atomizing head of the burner, and in some versions gaskets are fitted to prevent this. Steam is left on all the time the burner is in operation, even when the oil is turned off, in order to cool the burner and prevent any remnants of oil in the burner passages from carbonizing. Safety shut off valves are fitted to the burner carrier; these are opened by projections on the burner so that oil and steam are automatically shut off when the burner is removed.

Preservation of boiler

Store the boiler to prevent the corrosion by eliminating air and dissolved gases.

Long term storage:-

1. Wet storage:- Using a corrosion inhibitor, like a mixture of sodium nitrite and borate at concentration of 1000 to 3000 ppm of each chemical; The boiler must be drained and washed out to remove these inhibitors before it is prepared for steaming.

2. Dry storage:- Completely emptying the boiler, drying out by gentle heat and then inserting, trays of lime or silica gel and sealing the boiler. (2-5kg of quick lime or 1.8kg silica gel/tons of water). Check the absorbent every one to two weeks then every one to three months, renew if required. The external surface is protected against corrosion by using appropriate cleaning techniques. Vanadium & Sulphate condensates on external surfaces will produce strong acids.

Short term storage:- Completely fill the boiler with alkaline water containing sufficient hydrazine to combine with dissolved oxygen and leave an excess of hydrazine; for short period up to three days. The excess hydrazine should be at least 25ppm N2H4, Before sealing the water should be raised to the boiling point to introduce mixing by circulation and to complete the chemical reaction.

a) When these methods are used, precautions should be taken to prevent atmospheric condensation up on the fire side surfaces of the boiler, which would lead to severe external corrosion.

b) Wet storage method is not advised in which the water in the boiler or pipe work could freeze during idle periods.

Wet lay up method:- After shutting off the firing, when the boiler is being cooled down excess amount of NaOH, Na2HPO4 & N2H4 added to the boiler water by chemical injection system as to make phosphoric acid (PO4)3- 50ppm; Ph-10.5; N2H4-100ppm.

a) When the pressure has gone down to nearly zero; open the steam drum air vent valve.

b) When the pressure is almost off the boiler, fill the boiler with distillate water, until water comes out from the vent valve & then close the vent.

c) Put the hydrostatic pressure about 4kg/sq-cm. on the boiler until the boiler has completely cooled down to boiler room temperature, then again bleed air from air vent valve. Hold a hydrostatic pressure about 2kg/sq-cm.

To bring the boiler back to the service, bring down the steam drum water level by blowing down and adding make up water level by blowing down and adding makeup water, so that boiler water concentration down to normal value.

Steam from cold condition

Boiler is considered to be having no steam available, Boiler has to be first flashed on diesel.

(a) If the boiler had been opened up for repair or survey, it must be thoroughly checked up to see that all the doors, mountings and attachment have been properly boxed back.

(b) All the valves should be kept in the operating position. i.e feed check valve open, blow down valve shut, steam stop valve shut, air vent open, pressure gauge & gauge glass steam and water cock open drain cock shut and safety valve ungagged.

(d) Check that all valves in the fuel oil line in working position.

(e) The furnace is thoroughly purged with air for at least about 5 minutes. Start fuel oil circulation. A burner with smallest orifice is used and is set on fire at the lowest rate possible.

(f) The flushing up should be gradual and intermittent firing- firing for 5 minutes and stopping for half hour for three or four times and the interval between the firing is gradually reduced. Every time before firing the furnace should be thoroughly purged to avoid back fire. The rise in temperature should not exceed 6-7 degree Celsius per hour and at least 18 to 24 hours should be taken to rise steam. This is to provide undue thermal stress, being setup in the boiler structure. Water heating is taken place by convections of currents this leaves the cold water below the furnace cold. If a water circulation arrangement is available the time can be reduced to 12hours. After rising of steam to a pressure of 1 bar, close the air vent valve. Nuts on the Man-Hole Doors and any new joints should be nipped up. Now boiler pressure can be increased gradually up to operating pressure. If no circulation arrangement is provided, blow down valve can be opened to remove the cold water.

Boiler and feed water troubles

Q. With reference to Boiler water tests carried out onboard:

A. Discuss the possible reasons for the following changes in boiler water test results, and state what actions should be taken in each case;
1. Reduction in total dissolved solids and chemical reserves.
2. Reduction in phosphate reserve, with increase in chlorides and total dissolved solids;
3. Reduction in alkalinity reserve only.
4. Increase in oxygen levels only.
B. State why the complete results of boiler water tests are logged or entered into a data retrieval system rather than a note being made of any particular result which may be outside set limits.

Answer:- (A) Possible reasons and actions:-

1. T.D.S and Chemical reserve in the boiler can be reduced because of the water leakage from leaking tubes or because of any other source of water leakage. Actions to be taken:- water leakage from tube can be seen as white smoke from the boiler funnel along with frequent level drop in boiler drums which leads to frequent requirement to refill the cascade tank. Also the boiler may fail to fulfill the required demand of steam. Trace the leakage and repair the same, carry out adequate chemical treatment.

2. Reduction in phosphate reserve, with increase in chloride and T.D.S can take place if the sea water leakage in the system. Actions to be taken:- sea water can enter in the system through condenser system. Trace the source of sea water leakage in the system.

3. Reduction in alkalinity reserve only takes place when lube oil with high alkalinity leaks in. Actions to be taken:- lube oil can enter through the purifier feed heater. same needed to be traced and rectified.

4. Increase in oxygen levels only takes place when ingress of air takes place. where de-aeration system uses vacuum principle it is more prone to air ingress. Actions to be taken:- Trace the source of air ingress and it can be from defective flanges, gaskets, uncovered cascade tank or cracked valve bonnets. Maintain temperature of hot-well and check for the ventilation of the from de-aerator.

(B) By logging the boiler water test results we can follow the gradual trend of value deviation within the normal range. This record is helpful in scheduling the chemical treatment.

1. Problems with condensate & boiler system:-

a. Corrosion

b. Scale formation

c. Carryover & prevention.

2. Scale formation:- The physical form of scales depends on the constituents present in water.

[A]. The soluble calcium & magnesium salts are the causes of hardness of water. a. If the fresh and shore water is used most of scale formation occurs.

b. The bi-carbonate of calcium and magnesium can easily decompose by heat causing alkaline or temporary hardness.

c. The insoluble carbonate can be precipitated, if not removed by boiler blow down.

d. The CO2 is liberated in the boiler will produce an acid steam condensate.

[b] The chlorides, sulphates and nitrates {CaCl2, MgCl2, CaSO4, Ca(NO3)2 & Mg(NO3)2} are not decomposed by boiling.

a. They Causes non-alkaline hardness or permanent hardness.

b. The effect of adherent scale and deposits form a thermal insulator of on heating surfaces leading high metal temperature causing rapture.

3. Prevention from Scale formation:-

a. Good quality evaporated sea water to be used.

b. Avoid loss of condensate from the system.

c. Avoid contamination by salt water.

4. Carryover:-

a. Contamination of steam by boiler water, solid and foaming can interfere turbine efficiency, form deposits on super-heater turbine blading, etc.

b. Causes:- High water levels, steaming in excess of boiler rating, sudden increase in demand, High concentration of dissolved solids.

c. Prevention:- as per the causes.

5. Foaming:- It is small stable bubbles collect over the boiler water surface. Increase in suspended and dissolved solids, oil or organic matter causes foaming.

6. Types of corrosion in Condensate system and Boiler:-

a. Pitting

b. Thinning,

c. Caustic corrosion,

d. Caustic cracking,

e. Corrosion fatigue,

f. Stress corrosion,

g. Embrittlement,

h. Exfoliation corrosion,

i. Graphitization,

j. De-zincification,

k. Ammonia corrosion,

l. Oxygen corrosion,

m. CO2 Corrosion,

n. Acid corrosion.

7. Properties of fresh water:-

a. Rain water absorbs CO2 from air and form dilute Carbonic acid.

b. Its solvent action on minerals and rocks is thereby increased.

c. Rain water dissolves calcium carbonate and holds it in solution as calcium bi-carbonate. CaCO3 + H2O + CO2 = Ca(HCO3)2

d. Other dissolved compounds are Sulphate, Chlorides and Nitrates { CaSO4, CaCl2, Ca(NO3)2, MgSO4, MgCl2, Mg(NO3)2, Na2SO4, NaCl, NaNO3 }.

8. Hardness:-

a. Hard water:- Calcuim & Magnesium salts. They are Alkaline in nature. When heated leads to scale formation.

b. Soft water:- Mainly Sodium salts. They are acidic in nature. They can cause corrosion but does not form scale. Alkaline hardness salts are hydroxide, carbonates and bi-carbonates (temporary hardness) of calcuim and magnesium. Non-Alkaline hardness salts are chloride, sulphates, nitrates and silicates of Ca & Mg ( Permanent hardness). Chemical treament is reqired to remove this hardness. Total hardness is the sum of the alkaline and non-alkaline hardness. Non-hardness salts:- Sodium salts remains in solution and do not deposit under normal boiler condition.

9. Gaseous Corrosion:-

a. Oxygen corrosion:- O2 dissolved in water & cause corrosion, the severity of O2 attack depends on the concentration of dissolved O2, PH value & temperature of water. It reacts with the ferrous metal surfaces to form red iron oxide (Fe2O3) which appears as pitting. Since this ferric oxide or rust is porous and does not protect metal surface, the corrosion process continues.

b. CO2 Corrosion:- Heat causes carbonates (CO3-2) & bicarbonates (HCO3-1) dissolved in water to breakdown to CO2. CO2 reacts with water form weak carbonic acid which causes corrosion of iron and copper metal.

c. Ammonia corrosion:- Ammonia formed by the decomposition of hydrazine can enter the feed system. It will the dissolve any cupric oxide formed on copper or copper alloys tube. It will not attack the copper metal and so if no O2 present the process ceases. However any oxygen present can now attack the copper metal to form a thin film of cupric oxide, and the process repeats for further attack by the O2.

10. Protection against gaseous corrosion.

[A] Mechanical correction

a. check possible point of air ingress leakages in condensating and vacuum section. Defective flanges, gaskets or valve packings, or cracked valve bonnets, open return line drain valve, in sufficient steam pressure on gland seal.

b. Check the temperature of water in tanks operating at atmospheric pressure, water should be heated at highest temperature with vapour lock.

c. Avoid O2 concetrated water drains into the hotwell.

d. Check the efficient operation of dearating heater. Water temperature should be nearly equal to steam temperature.

e. Make up feed water to be taken slowly, Otherwise the deaerating heater will get overloaded.

[B] Chemical treatment

a. Sodium Sulphite(Na2SO3) can be used in low pressure boilers, Catalysed Sodium Sulphite reacts rapidly with oxygen. It Should be added directly to the boiler, not as a conteneues feed.

2Na2SO3 + O2 = 2Na2SO4

b. Hydrazine(N2H4) reacts with O2 produce N2 and water. Excess N2H4 is the boiler breaks down to give ammonia which provide suitable alkaline condition in condensate system, which counteracts the effects of CO2 corrosion.

N2H4 + O2 = 2H20 + N2

c. Neutralizing amine (e.g Cylohexylamine or Morphalene); ( SLCC-A-Condensate corrosion inhibitor); Removal of balanced CO2 after efficient deaeration. CO2 form weak (carbonic) acid. Adjustment of PH minimizes theeffect of acid. In condensate system to prevent corrosive effect a continuous doasage of Neutralizing amine is essential.

11. Acidic Corrosion

a. Acidic attack of boiler tube and drum is usually in the form of general thinning of metal surfaces.

b. Presence of CO2 causes acidic condition if condense CO2 + H2O = H2CO3 ( Carbonic acid)

c. If sea water leakage, magnesium chloride (MgCl2) Introduced in boiler system. MgCl2 + H2O = Mg(OH)2 + 2HCl {reversible reaction}.

d. Maganesium Hydroxide has a low solubility, can deposit and form scale but with suitable tratment it can be precipitated into the form of a non-adhearent slugdge which can be blown out of the boiler. e. Hydrochloric acid attack metal surface, specially below the deposits, also lower alkalinity.

12. Preventaion from acidic corrosion.

a. Mechanical corrosion:- Prevent leakage of condenser tubes.

b. Chemical treatment:- Maintain recommended alkalinity (or PH) which will eliminate the possibility of acid attack.

13. Caustic corrosion

a. It results in presence of excess from NaOH. It occurs in H.T regions where due to rapid evaporation, concentration NaOH (Sodium hydoxide) formed especially below the deposits on heat transfer surface severe localized corrosion taking place.

b. Characterized by thinning of the metal in irregular patterns.

14. Prevention from caustic corrosion

[A] Mechanical correction

a. Boiler should be maintained in clean condition.

b. Blow down if required.

c. Overloading should be avoided.

d. Fuel oil atomisation & burner alignment required to avoid hot spot.

[B] Chemical treatment:- maintain recommended alkalinity.

15. Caustic Cracking This is form of inter-crystalline cracking caused by water with a high level of caustic alkalinity; coming in contact with steel has not been stress relived. As a preventive measure stress point to be checked periodically and treatment of water should be adequate.

16. Corrosion fatigue

a. It also called stress corrosion generally occurs in HT area of tubes, where irregular water circulation has been experienced as alternating stresses, have been setup in the tube material.

b. Series of fine cracks in the tube well aggregated by other corrosive condition. Ultimately tube failure.

c. If a material subjected to fairly heavy alternating stress is placed in a corrosive environment can lead to formation of fatigue cracks.

d. For the prevention against corrosion fatigue, special care should taken for increased or decreased steam pressure & flame characteristic to avoid hot spot and keep boiler water must kept alkaline.

17. Embrittlement & Prevention

a. This type of corrosion results in cracks of the tube metal, damaging of the internal structure of the metal.

b. The hydrogen atom are generated by concentrated acid water under hard dense deposit.

c. Hydrogen ion react with carbon atoms present in steel to form methane (CH4). Methane is a large gas molecule which exerts internal pressure within the metal. The H.P causes the grains of steel to separate and fracture.

d. Hydrogen attack can occur rapidly, tube fails & rapture. e. Phosphate assist in inhibiting hydrogen embrittlement.

18.[A] Pitting:- A localized metal attack by formation of rounded deep cavities. It also found in way of water level in boiler shell during poor storage procedure. [B] Thinning:- General corrosion or metal loss in which thickness of metal is evenly reduce over a large surface area especially in way of heating surfaces such as tube wall.

[C] Exfoliation corrosion:- A type of attack which peels or splinter the metal into thin, parallel layers. This is called de-alloying. It occasionally occurs in cupro-nickel tubes where nickel is selectively oxidized from the alloy, resulting in layer of copper metal & nickel oxide.

[D] Graphitization:- When unprotected cast iron exposed to sea water, the metal corrodes away leaving behind a skeleton comprised mainly of graphite flakes. These have virtually no strength and when the surface is removed collapse into carbon dust.

[E] De-Zincification:- this can occur when brass with a high zinc content is in contact with S.W. As the brass corrodes away the Cu-component of the alloy is re-deposited back onto the surface, so giving in effect the removal of zinc.

19. Sodium Sulphite vs Hydrazine.

[A] Sodium Sulphite:-

a. It increases dissolved solid content.

b. Sodium Sulphite PH 7; Hence the sodium sulphite should be injected into the system before any alkaline ingredients.

c. In H.P boilers, the sodium sulphite can breakdown to give H2S, SO2 which can attack steal, brass & copper.

d. Catalysed sodium sulphite reaction with oxygen is extremely fast.

[B] Hydrazine:-

a. Does not increase dissolved solid content.

b. The uses of hydrazine results in a protective magnetic iron oxide firm (Fe3O4) on the boiler metal surface which act as an additional protection against O2 corrosion.

c. The excess hydrazine in the boiler breaks down to produce ammonia which provide suitable alkaline condition in steam/ condensate system counter acts the effect of CO2 corrosion.

d. N2H4 reaction with H2O is slow, thus continous dosing into the feed system is necessary.

e. Should be stored in a cool, well ventilated place since it is a fire hazard.

f. If the hydrazine reduce residual in allowed to be depleted, O2 will not be removed, magnetite film (Fe3O4) will not be converted to hematite (Fe2O3) red iron oxide, corrosion will begain again.

g. It is volatile & carry away with steam, it will protect non-ferrous metals in the condensate system. It also cupric oxide (CuO) is converted to cuprous oxide (Cu2O) which is less susceptible to corrosion.

Boilers and water treatment The major problems faced are:

a. Scale formation on the water-side of tubes and other heat transfer surfaces. b. Corrosion due to acid formation.

c. Problems due to excessive Alkalinity.

a. Scaled Boiler tubes:- Tubes get coated with scale over a period of time, which not only reduces the heat transfer rate, but also reduces the flow through the tube. The hard adherent scale is due to the presence of certain chemicals like, calcium sulphate, sodium and magnesium chloride and calcium silicate. These chemicals normally occur in water from shore supply, depending on the origin of the water. It is normally safer to generate the boiler feed water directly on-board with the Fresh water Generator, which produces distilled water that does not contain any of the above impurities. Scale may be hard or almost impossible to remove once it has formed a hard coating. The presence of scale also means that greater amount of fuel needs to be burnt to produce the same heating effect, viz. the temperature gradient across the heat transfer surface having scale is far more. This can lead to thermal cracks and eventual failure of the tubes. The secondary effect of scale is to reduce the flow through the tubes, which results in a fall in the circulation rate of the water, further aggravating the problem. The scale however, protects to some extent, the boiler surface from corrosive attacks. Temporary scale may be treated by a suitable chemical like Trisodium phosphate, which combines with the scale to neutralise it and form a coagulated compound, and settles down. This must then be removed by frequent Blow-downs of the Boiler drum.

(b). Acidic corrosion:- Oil finding its way into boiler water decomposes to form oleic and stearic acid. These acids float at the water level and corrode the surfaces that they come in contact with. Also, the acidic soap-like layer formed tries to prevent steam from escaping from the water surface, with the result that Foaming occurs. Oil can be removed at the Observation tank, since it floats on top. The filters there are capable of extracting the oil, and must be renewed if damaged or clogged.

(c). Excessive Alkalinity:- Excess of Alkalinity causes Caustic embrittlement and grooving of heat transfer surfaces. The level should be just sufficient to take care of any acids present, but if in excess, the Boiler should be frequently blown-down to reduce this. Over-dosage causes no adverse effects, and the above treatment should also be carried out when any pipe lengths are renewed, or tubes renewed. Ensure that proper cleaning is carried out before the treatment.

Preparing boiler for survey

Need for Boiler Survey:-

Flag State and Classification society regulations require that marine boilers be surveyed at specified intervals. Class Machinery status reports give details of past inspections of the boilers on board a ship and the due date range for the next inspection. Boilers are surveyed to meet the Class requirements during installation and commissioning. Subsequently, surveys are conducted at specified intervals to ensure that they continue to be fit for duty.

At the time of survey internal inspection and external examination are carried out. Regular internal and external examination during such survey constitute the preventive maintenance schedule the boiler goes through for a safe working condition.

Frequency of Surveys:-

Water tube main propulsion boilers are surveyed at 2 yearly intervals. All other boilers including exhaust gas boilers are surveyed at 2 yearly intervals until they are 8 years old and then surveyed annually. For auxiliary boilers of water tube type, the classification may allow the 2-year incidence to continue even often the expiry of 8 years period.

Scope of Surveys:- A complete boiler survey allows us to check out if any build-up of deposits has taken place, and deformations or wastage of plate work, piping or any of the various parts, which may compromise the safe working order of the unit. The survey should include finding reasons for any anomalies found and should also ensure that any repair carried out does not affect the safe working order of the boiler. A complete survey means full internal and external examination of all parts of the boiler and accessories such as super heaters, economiser, air-heater and all mountings. The examination may lead the surveyor to require hydraulic testing of pressure parts or thickness gauging of plate or tubes that appear to be wasted and eventually assign a lower working pressure. The collision chocks, seating stools and rolling stays are also to be checked for good working condition.

Shutting down a boiler for inspection or repair:

(a) Read and follow maker's instruction manuals and company procedures. All personnel involved should wear PPE i,e. helmet, safety shoes, hand gloves, etc.

(b) Issue work permits mentioning the nature of work, scheduled work time and persons involved. Inform the chief engineer, duty officer and post necessary notices. Soot blow the boiler and change the boiler control from automatic to manual.

(d) Switch off the main power and turn off the air circuit breakers for the combustion control panel, the forced draught fan, the fuel oil pump and the boiler feed water pump dose the main and auxiliary steam-stop valves.

(e) Let the boiler steam pressure drop to 1 bar. Open the air vent to avoid vacuum formation and allow the boiler to cool down. Open the blow-down to empty the boiler drum.

(f) Ensure boiler is drained and is sufficiently before opening up.

(g) Loosen the nuts on the top manhole doors and gently knock the door into ensuring there is no residual steam pressure. Open the top doors first, and then the bottom doors.

(h) Open the furnace door taking necessary precaution. Thoroughly ventilate the boiler for 12 to 24 hours. Personnel should not enter boiler, furnace or flue until the unit has cooled sufficiently.

(i) Ensure all connections to drum are either blanked off, removed or valves locked in dosed position with posted notices.

The survey is not complete until the boiler has been examined under steam and the following items dealt with:

(a) Pressure gauge checked against a test gauge.

(b) Testing of water level indicators and protective devices.

(e) Testing of remote control gear for oil fuel shut off valves.

Arrangement before Survey (a) Boiler must be sufficiently cleaned and dried to make a thorough examination possible. Sludge deposits continue to be the prime cause of non-operation of internal controls and overheating of furnace in vertical boilers. Boilers should be manually wire-brushed to clean the internal surfaces. In case of difficulty in manual cleaning, a chemical cleaning with hydro-chloric- acid plus an inhibitor to prevent acid attacking the metal without affecting removal of deposits is the best procedure. For oil contamination, alkali boil-out using tri-sodium phosphate solution (which produces a detergent action) is essential prior to acid cleaning. A thorough water flushing must be carried out after acid cleaning to avoid acid concentrating in crevices and captive spaces. (b) All internals which may interfere with the inspection has to be removal. (c) Wherever adequate visual examination is not possible, surveyor may have to resort to drilling, ultrasonic or hydraulic testing. (d) All manhole doors and other doors must be opened for a reasonable time previous to survey for ventilation. (e) If another boiler is under steam arrangement of locking bar and other security devices must be in position preventing the admission of steam or hot water to the boiler under survey, The smoke trunking (separating device), exhaust-gas shut-offs etc. must also be in position and in proper working condition. (f) Ship's staff or repairer's staff should stand by the manhole in case of emergency and to note any repairs required. 1. Fuel oil burner put off, pump stopped and fuel oil line shut and isolated. 2. Air supply to the furnace shut after purging. 3. Main aux steam stop valve kept shut and hand wheel removed. 4. 3/4th gauge glass water taken to the boiler for proper scum blow, then all feed check valves kept shut and hand wheel removed. 5. Allow boiler pressure to fall about 4-5 bar naturally or by easing gear. 6. Boiler ship side blow down cock is to be opened, then boiler to be scum blown so that oily grease can bot adhere to the internal surfaces. After scum blow down, valve to shut, then bottom blow down valve to be open slowly and boiler to be blow down completely, Initially open the valve fully for 3-4 seconds so that sudden surge of water carried the sludge with it. Repeat 3-4 times, then close bottom blow down valve and then ship side blow down cocks. 7. The vent cock is to be open at a pressure of one bar in order to fully release the pressure and destroy the vacuum, otherwise a serious accident may occur while opening the manhole door. 8. The top manhole door is to be knocked first otherwise if bottom door is opened first, there is a danger of being met with a rush of scalding vapour when the top door is knocked in, the person may meet serious accident, the top manhole door is to be tied with a rope, the dog nut are to be slackened and the door joints broken, person should stand well clear off the door. After removing nuts and dogs, the door to be removed. 9. After knocking the top door the bottom manhole door to be opened in a similar manner. when doing so the person should stand well clear in case there is any hot water present inside. 10. The boiler is allowed to cool down and ventilated by natural circulation of the air and it is ready for cleaning next day. No naked light is allowed near the boiler until it is ventilated due to danger of explosive gas in the boiler. 11. Periodical Surveys of boilers and other pressure vessels to carried out as required by the Rules and the safety devices to tested. External visual examination. External examination of boilers including test of safety & protective devices and test of safety valve using it's relieving gear. For exhaust gas economizers, review of engine log book to verify that Chief Engineer has tested the safety valves at sea within the window period of Annual Survey.

Boiler tube failure and repair

Boiler tubes can fail / leak in the following conditions: a. Excessive corrosion of the tube, which reduces wall thickness to a value below that, which can safely withstand working pressures and stresses. b. This can be caused by oxygen pitting or under-deposit pitting. c. Overheating of the tube due to insufficient water flow, oil deposits or heavy scale formation, which insulates the tube, reducing heat transfer. d. Leakage at the tube/tube plate, use of improperly expanded tubes, increased mechanical stress and movement between tube/ tube plate, or 'forcing' of the boiler, which increases the temperature differential between the tubes, producing increased thermally induced stresses.

Note that the causes of tube overheating will also increase the frequency of tube leakage at the tube plate.

Tube failure and repairs:

The method to use, to rectify a tube leakage, depends upon various factors and the location. Obviously the best method is tube renewal, but lack of time / facilities mean that temporary repairs, like plugging of leaking tubes, must be carried out. Once a large number of tubes (more than 20%) are plugged, then the reduced efficiency of the boiler will make tube renewal more cost effective. It is also unsafe to operate with a large number of plugged tubes, since plugging is only a temporary solution, and may even lead to further failure. Temporary repair could be carried out by Using a plug or tapered stopper, which is fitted at both ends of the failed tube, and tightened into place by a long threaded bar fitted inside the tube. If time permits and suitable materials / spares allow a permanent repair to be carried out, then the failed tube must be removed and renewed. One method is to grind the tube flush with the tube plate, thus removing all the weld/ expanded section of the tube. The tube can then be punched-out. Inspection of the plate should be carried out to check for thinning/cracks. Remove all scale from the area of the weld by light grinding. Insert a new tube of proper rating (check material specifications or part number stamped onto the tube, to verify), and carry out the tube/plate attachment (either by expanding). Welding is the preferred method (less chance of tube /plate leakage), provided welding is carried out by an approved welder, using acceptable welding technique and consumables, and under the supervision of Class. The finished weld is normally inspected for visual defects, and by NDT. Hydraulic pressure testing should be carried out on completion, using warm water, to the working pressure of the boiler.

Question: Give the reasons for failure of Boiler tubes. How will you detect tube failure ? Discuss a temporary repair you could carry out, on a leaky Boiler tube, at sea.
Answer: Boiler tubes can fail / leak in the following conditions:
Excessive corrosion of the tube, which reduces wall thickness to a value below that, which can safely withstand working pressures and stresses. This can be caused by oxygen pitting or under-deposit pitting. Overheating of the tube due to insufficient water flow, oil deposits or heavy scale formation, which insulates the tube, reducing heat transfer.
Leakage at the tube/tube plate, use of improperly expanded tubes, increased mechanical stress and movement between tube/ tube plate, or 'forcing' of the boiler, which increases the temperature differential between the tubes, producing increased thermally induced stresses. Note that the causes of tube overheating will also increase the frequency of tube leakage at the tube plate.
Tube failure and repairs:The method to use, to rectify a tube leakage, depends upon various factors and the location.
Obviously the best method is tube renewal, but lack of time / facilities mean that temporary repairs, like plugging of leaking tubes, must be carried out. Once a large number of tubes (more than 20%) are plugged, then the reduced efficiency of the boiler will make tube renewal more cost effective. It is also unsafe to.operate with a large number of plugged tubes, since plugging is only a temporary solution, and may even lead to further failure.
Temporary repair could be carried out by :
1. Using a plug or tapered stopper, which is fitted at both ends of the failed tube, and tightened into place by a long threaded bar fitted inside the tube. If time permits and suitable materials / spares allow a permanent repair to be carried out, then the failed tube must be removed and renewed.
2. One method is to grind the tube flush with the tube plate, thus removing all the weld/ expanded section of the tube. The tube can then be punched-out. Inspection of the plate should be carried out to check for thinning/cracks. Remove all scale from the area of the weld by light grinding. Insert a new tube of proper rating (check material specifications or part number stamped onto the tube, to verify), and carry out the tube/plate attachment (either by expanding).
3. Welding is the preferred method (less chance of tube /plate leakage), provided welding is carried out by an approved welder, using acceptable welding technique and consumables, and under the supervision of Class.
4. The finished weld is normally inspected for visual defects, and by NDT.
5. Hydraulic pressure testing should be carried out on completion, using warm water, to the working pressure of the boiler.

Superheater tube arrangement

Disadvantages of parallel flow: - a- Large temperature difference at the end causes large thermal stress. The opposing expansion and compression of the material due to diverse fluid temperature can lead to material failure. b- The temperature of the cold fluid exiting the heat exchanger never exceed the lowest temperature of the hot fluid. This is contradictory to the design purpose to raise the temperature of the cold fluid, the design of parallel flow heat exchanger is advantageous when two fluids are required to be brought to same temperature. The contra flow has 3 distinguished advantages over the parallel flow design: - a- More uniform temperature difference between the two fluids minimise the thermal stresses through out the exchanger. b- The outlet temperature of the cold fluid can approach the highest temperature of the hot fluid. c- The more uniform temperature difference produces a more uniform rate of heat transfer through out the heat exchanger. In a heat exchanger or super heater the elements ends are of u shape. One section is entry and the fluid passes through the hollow elements and exit from the other end. Several elements are fitted with the common headers as a stack. As the free end is u shaped this will take care of the thermal expansion of the elements. But as the elements are long and free at the end they must be supported for proper securing against bending and vibration. This is usually done with the long strong steel support secured at the top casing frame and with suitable clamps are used for securing them with this support. Some dissolved solids (mineral salts) are present in water .When water starts boiling up some of the salts breaks into solid mass but can not be precipitated fully due to the abolition of water they remains as a solid particle. The greater the amount of solids in water the greater will be the tendency of water to from foaming or froth. In a steam drum the top space is for steam accumulation. There is an interface of steam and water level the steam come as a bubble and burst at the top surface. Due to concentration of dissolved solids during bursting of these bubbles the solid will carry along with the steam this is known as carry over. This solids will go and deposit on the inner surface as a layer or incrust. Which will impair the proper heat transfer due to its insulated nature, the heat transfer efficiency will reduce and in the long run may structurally damage the components. Note:- 1) Contra flow arrangements ensure that the temperature difference at any corresponding location of the coolant & cooled fluid is constant, This ensures that the heat transfer process is devoid of thermal stress. Where as in parallel flow system the temperature difference at any entry is high & at exit is low, Thereby the temperature difference is not constant & will induce thermal stresses. The heat extraction is more in contraflow than parallel flow. 2) The elements tubes are supported by long steel rods with suitable clamps supported from the top casing frame of the super-heater bank arrangement. 3) In a carry over condition solids particles from boiler water will pass away along with the steam and will deposit on the elements. Which will effect for proper heat transfer.

Plan to reduce uptake fire

The uptake fire if occurring frequently in an auxiliary boiler, the problem is not so easy to eliminate immediately. The cause of uptake fire which is caused mainly due to accumulation of soot and unburnt carbon particles which are sticking to surfaces in the up take, due to incomplete combustion. In an auxiliary boiler, the flue gases normally pass through economizer or air pre heater or feed water heaters. All these types of heat exchangers are fin types. Hence large amounts of soot deposit on the fins. Along with the flue gases some un burnt carbon particles also get deposited on the fins of heat exchangers. Normally dry soot deposits have a very high ignition temperature, but when soot gets wet with some hydrocarbon vapours, their ignition temperature may come down to as low as 150 deg cel. This may result in boiler uptake fire, by cleaning and washing the deposited soot may reduce the up take fire temporary but for permanent or long lasting solution other factors for accumulation of soot to be checked and necessary preventive action to be taken, this is little time consuming and tedious job but can reduce the occurrence to a great extent. For long lasting solution a plan to be drawn and implementation must be carefully monitored. As the main cause for soot fire is the unburnt carbon particles which generates due to incomplete or erratic combustion, to eliminate this the following steps to be adopted, (1) Regular inspection of boiler flame to ensure correct air fuel ratio is maintained. This will help proper and efficient combustion. (2) Oil may drip without atomizing due to defective or clogged burner tips and swirl plates, the cleaning and inspection to carry out at regular intervals as per PMS. (3) If the grade of fuel oil is not suitable, difficulties in proper combustion can be faced. To ensure proper grade and treatment is being maintained. (4) The line filters strainers should be clean, fuel oil heater temperature should be maintained not too low or high. (5) Furnace to be kept clean. (6) Regular soot blow (either by steam or air) will drive away the adhered soot components, the soot blowing equipment and line valves should be checked and to be ensure they are in working condition. (7) In spite of regular soot blow operation the heat exchangers inside the uptakes (if fitted) to be water washed periodically at convenient place and time, with proper protection and safety. (8) Prolong low load operation can cause improper combustion leading to formation of soot, such operation if not necessary to be avoided. (9) The boiler should be operated at full load periodically, which will help to drive away the accumulated soot. 10) Periodic use of soot remover chemicals like soot sticks or equivalent during combustion. 11) The up-take and the flame screen on top of the tunnel to be checked and if necessary to be cleaned. Considering all above facts a maintenance plan to make and the engine room watch keepers to be allotted for particular jobs as repair/ cleaning and to be recorded in regular basis. The engine room personnel to be allotted for various work considering their experience and capacity for example in every watch the flame to be checked and if any deviation noticed to be corrected by the senior watch keeper and action for correction to be recorded and signed. The second engineer will personally check and counter signed periodically (weekly) to make sure every thing according to plan is being carried out. Immediate action to reduce the occurrence temporary, to stop the boiler with the permission from office at suitable time, place as convenient en-route for couple of hours, and sweeping out the soot and then wash down the fins of the heat exchangers, in mean time furnace inspection and boiler burner cleaning to be carried out. For prolong solution the routine to follow regularly.

Theory of boiler uptake fire:-

A fire in the exhaust gas boiler on a motor ship may develop in two or three stages. They are;

(i) Ignition of soot:

(ii) Small soot fires;

(iii) High temperature fires.

(i) Ignition of soot:- -Ignition of soot may arise in the presence of sufficient oxygen when the deposits of combustible material have a sufficiently high temperature (higher than the flash point) at which they will liberate sufficient oil vapour, which will be ignited by a spark or a flame. The main constituent of soot deposits is particulates present in the exhaust gases, but in addition some un-burnt residues of fuel and lubricating oil may be deposited in the boiler due to faulty combustion equipment (like leaky fuel valve, improper lubrication etc.) Or especially in connected with starting and low speed running of the engine. The potential ignition temperature of the dry soot is laid in the region of 300 to 400°C, but the presence of un-burnt oil will lower the Ignition temperature to approximately 150°C. This means that ignition may also take place after shut down of the main engine - Even with an ignition temperature of the layer above the boiler tube wall temperature, glowing particles (sparks) in the exhaust gas may start a soot fire.

(ii) Small soot fire -Small soot fires in the exhaust gas boilers are most likely to occur during manoeuvring with the main engine running on low speed operation. During low speed operation the combustion process in the engine cylinder is not efficient causing carryover of un-burnt fuel which gets deposited it its exhaust path like in EGB - Due to the presence of oxygen in the gas the deposited soot on the EGB tubes may attain high temperature and reaching ignition temperature they become glowing particles and leads the generation of a soot fire. Small soot fires do not cause damage to the exhaust gas boiler on the damage is limited, but the Fires should be carefully monitored and appropriate action should be carefully monitored and appropriate action should be taken. -Continued circulation of boiler water, cause the major part of the heat to be conducted away causing the fire to cease. Combustion gases are also responsible to some extent for carrying away the heat -The probability in a small soot fire is very low that the tube wall temperature will rise sufficiently to start an iron. On hydrogen fire, provided water circulation is maintained steam on water leakages are not present (iii) High temperature fires: Under certain conditions a soot fire may develop into high temperature fire. Hydrogen fire - this occurs due to the fact that water dissociates into hydrogen and oxygen, in connection with carbon monoxide and hydrogen may occur certain conditions. Hydrogen fire will start if the temperature is above 1000°C. -Iron fire- an iron fire means that the oxidation of iron of high temperature occurs at a rate sufficiently high to make the amount of heat release from the reaction sustains the process. These reactions may take place at a temperature In excess of 1100 C. In this connection, it is important to realize that, water may also go in chemical reaction with iron i.e. the use of steam based soot blower may also feed the fire. -A small soot fire may develop into a high soot fire involving the following reactions. Hydrogen fire, temperature above 1000°C Dissociation of water into hydrogen and oxygen Iron fire-This may cause burning of tubes

Plan to reduce boiler uptake fires:- For the objective of prevention and reduction of boiler uptake fire we require to follow a proper practice of engine operation and timely maintenance. for which manufacturers recommendations must also be considered. The areas of avoidance to be pointed out and rectified. Following are steps for Prevention of Fire. (a) Check the bunker lab report before it is put into use. The quality must meet the standards required by manufacturers recommendations. (b) Maintain the main engine properly to acheive proper combustion of the fuel. (c) Maintain the boiler burner to achieve the proper combustion of the fuel. (d) regular washing of turbocharger to be carried out. (e) Avoid slow steaming of main engine (f) Ensure good fuel combustion in the main engine (g) Ensure fuel is treated and is of good quality while supplying to the engine. (h) Do regular soot blow of boiler tubes. (i) Do water washing in ports at regular interval. (j) Ensure design of exhaust trunk to be such to provide uniform heat to complete tube stack. (k) Pre-heated circulating water to be supplied to boiler mainly at the time of start-up. (l) Circulating pump should not be turn off at any time while main engine is running. (m) Do not stop circulating pump for at least two hours after the main engine is stopped. (n) Start circulating pump prior to 2 hours before starting the main engine

Monitoring the progress of plan Monitoring of progress of a plan towards a goal is equally important as the implementation of the same. The monitoring of the progress involve the following areas which required to be inspected/checked. (a) check and compare the log book reading and compare the parameters to ensure the implementation of plan is progressive. (b) frequently inspect the uptake for the deposition of the soot. (c) frequently check the exhaust gas color to analyze the combustion quality. (d) check the quality of washed out water from turbocharger and economizers to know the improvement in condition. (e) compare the slow steaming hours and discuss the results with chief engineer and captain. (f) keep record of all the circulation pump stating and stopping times to know that they were in operation for how long after engine stopped.

standing instructions you will issue to the watch keepers Standing Instructions: (a) In case a soot fire develops in the exhaust gas boiler it will be indicated by high uptake temp. (b) Sparks emission from funnel (c) High flue gas temperature alarm (d) Steam pressure increases abnormally and safety valve on the are boiler lifts In such a situation the following actions should be followed depending on the level of fire 1. Raise engineer's alarm 2. Inform Bridge and stop the engine, this will stop the feed of oxygen to the fire 3. Continue operating the boiler water circulating pump keeping an eye on the auxiliary boiler water level gauge to confirm that there is as tube failure 4. Never use soot blowers for lighting the fire as it may involve the risk developing into an iron fire 5. Stop air circulation through the engine by covering the turbocharger fitters and operating the air for closing the exhaust valve 6. Never open any inspection doors of the economizer until the economizer has cooled down sufficiently. 7. Once the economizer is cooled, Inspection door should be opened, and thorough water washing should be carried out, keeping the boiler water circulating pump running. An inspection should also be carried out to check for any damages. In a well-run plant, any fire that starts, will be small, if the above emergency actions are taken immediately, the fire will be damped down quickly, and water circulation will help to cool the tubes and reduce heat damage caused by fire. If the soot fire has not damped out and is increasing followed by a loss of water (like Indicated by too low boiler water level on gauge on excessive feed water consumption) then there is a possibility that the soot fire has turned into an iron fire on hydrogen fire. 1. In such situations the following actions should be taken 2. Stop the main engine, if it has not been stopped already 3. Stop the boiler water circulating pumps immediately 4. Close the valves on the circulating line 5. Do not use soot blowers 6. Drain out the water from the exhaust gas boiler 7. Do not open any inspection door of the EGB 8. Carry out boundary cooling of the EGB 9. If fire fighting gas is available, and is possible to slightly open the Inspection door, then inject the fire fighting gas through the inspection door. 10. Once the fire has reduced, cool down by plenty of splash water on the heart of the fire. Care should be taken when using water, otherwise it may turn into hydrogen fire, and thus a large amount of water should be applied directly on the heart of the fire. 11. Once it is Confirm that the fire has died down, carry out thorough water washing, and then check the Inside of the economizer to assess the extent of damage. If now the engine has to be started (like during maneuvering) and the economizer is damaged then dry operating of the economizer should be carried out as follows. 1. After cleaning and draining of the economizer, open the air vent valve. Do not start the boiler water circulating pump 2. Start the engine, and avoid low speed operation an as much as you can 3. Carry out frequent soot blowing 4. Once the maneuvering is complete, repair the damaged parts as soon as possible.

Corrosion protection of steam line

The outside surface to be insulated with some light bonded mineral wool padding with stainless steel wire netting, this become the primary barrier. The padding to be covered with some metal jacket fastened and bonded to prevent water entry at joints or where insulation are supported with attachment angles. Cement coated insulation can be finished with a suitable water proof mastics to prevent water ingress. The type of insulation and method of application should be chosen assure the absence of any shrinkage cracks. wrapping equipment with aluminium foil before applying insulation will reduce the risk of corrosion. Boiler external surface- The entire exposed area to be covered with lightly bonded mineral wool mattresses of density 150 kg/m3 for surface temperature above 400 deg cel. and with density 100kg/m3 for lesser temperature with S.S netting. For every subsequent layer of mattresses with G.S wire netting. The total thickness could not be less than 3mm. The outer surface should be covered with aluminium metal sheet and circumferential over lapping should be tightly bonded with self tapping metal screws or to be riveted. keen observation during operation to be implemented so that no cover is damaged or detached, causing ingress of moisture which will be soaked by the insulation and permanent source of corrosion will expose. (a) The internal surfaces of steam lines are affected by air corrosion caused by condensed water remaining inside with air, when the steam is shut off. Corrosion is caused by a warm and moist atmosphere within the pipes. Hence the pipes should be internally coated with a good polymer paint which is coated over the galvanized surface. To maintain this surface in good condition , it is the function of the ship’s staff to ensure that the lines are drained properly when not in use. The external surfaces are to be coated with a strong heat resistant primer paint and then properly insulated and further protected by metal cladding to protect the insulation. The function of the manufacturer / fabricator is the internal coating and external coating as well as the insulation. When pipes are renewed the ship staff should ensure that the pipes are properly protected in the manner stated above. (b) The external surfaces of auxiliary boilers are to be coated with at least two coats of good quality heat resistant paint and then covered with an adequate thickness of insulation. The insulation is further protected with steel cladding of at least 3 mm thickness with binding steel straps. This is the job of the manufacturer. The ship staff function is to ensure that during boiler surveys followed by repairs the damaged portions of the insulation are properly restored. (c) The internal surfaces of water boxes are coated with at least two coats of bitumastic slow drying anti corrosive paint and further fitted with adequate size of zinc slab to prevent galvanic corrosion. This is the job of the manufacturer when the cooler or condenser is new. Subsequently during service when cooler boxes are opened by ship staff for cleaning, they should ensure that the boxes are restored to the same standard as mentioned above. (d) Main sea water pipes leading from the sea chest to the sea filter and up to the intermediate valve are internally coated with a thick layer of good quality polymer paint by the manufacturer when the ship is new. Subsequently during every dry-docking it is recommended that ship owners follow this procedure if sea water pipes are to last longer..

Combustion process

In a furnance, chemical energy in the fuel is converted into heat by the process of combustion. The forced draft fan supplies the primary and secondary air required for atomisation and combustion. The primary flame heats the heavier constituents of the fuel to their ignition temperature. The larger oil droplets are heated in their passage through the primary flame zone, vaporised and burnt. The swirl vanes in the air register create flow patterns in the secondary air stream. This provides heat to the surrounding furnace for the generation of steam. Complete combustion requires continuous vaporisation of the fuel. The process takes place in four stages namely, heating, atomisation, hollow cone and suspended flame. a. Heating:- Heating of oil is carried out in steam or electric fuel oil heater. Heating reduces its viscosity and makes it easier to pump and atomise. b. Atomisation:- The heated oil passes through the burners where it is sprayed as fine particles. As a result, oil with a large surface area is produced for combustion. c. Hollow cone:- The burner imparts rotational energy to the fuel so that fuel leaves the burner tip as a hollow, rotating cone of fine oil droplets. d. Suspended flame:- A stream of oil and air particles enters the combustion zone at the same rate at which the products of combustion leave it. Therefore, actual flame front remains stationary, while the fuel undergoes combustion. Explanation:- The oil is first heated in steam or electric fuel oil heaters. This reduces its viscosity and makes it easier to pump, filter, and finally to atomize. However it must not be overheated at this stage, otherwise a process known as 'cracking' occurs, leading to carbon deposits, and the formation of gas in the fuel oil lines, etc. The gas, due to its large volume, reduces the mass of oil passing through the burners, which in turn leads to a possible reduction in the steaming rate of the boiler owing to the reduced amount of fuel actually burnt. This gasification can also cause instability in the combustion process itself, resulting in a fluctuating flame formation. The heated oil is now passed through the burners where it is atomized; this process breaks it up into a fine spray of droplets, so presenting a very large surface area of oil to the combustion processes. The droplets formed are of two main types, i.e. very fine particles consisting of the lighter fractions of the fuel, which form a fine mist, and slightly larger droplets formed by the heavier fractions of the residual fuel. The burner also imparts rotational energy to the fuel so that it leaves the burner tip as a hollow, rotating cone formed of fine droplets of oil. The combustion stage itself can now commence, and in a boiler furnace a type of combustion often referred to as a 'suspended flame' is used. For this a stream of oil particles and air enters the combustion zone at the same rate at which the products of combustion leave it. The actual flame front therefore remains stationary, while the particles pass through it, undergoing the combustion process as they do so. The combustion zone itself can be sub-divided into two main stages; these are referred to as the primary and secondary flames. Primary flame:- For the oil to burn, it must be raised to its ignition temperature, where continuous vaporization of the oil required for its combustion takes place. This temperature should not be confused with the flash point temperature of the oil, where only the vapour formed above the oil in storage tanks, etc. will burn. The ignition or burning temperature should normally be at least some 20°C above this value. For the reasons already stated this ignition temperature cannot be obtained in the fuel oil heaters, and therefore the heat radiated from the flame itself is utilized so that, as the cone of atomized oil leaves the burner, the lighter hydrocarbons arc rapidly raised to the required temperature by the heat from the furnace flame; they then vaporize and burn to form the primary flame. The heat from this primary flame is now used to heat the heavier constituents of the fuel to their ignition temperature as they, together with the incoming secondary combustion air, pass through the flame. The stability of the combustion process in the furnace largely depends upon maintaining a stable primary flame and, to ensure it is not overcooled. A refractory quart is usually placed around it so as to radiate heat back to flame. The primary flame should just fill the quart. If there is too much clearance excessive amounts of relatively cool secondary air enter the furnace; too little and the heavier oil droplets impinge on the quad and form carbon deposits. Another important factor for the formation of the primary flame is that it must be supplied with primary air in the correct proportion and at the right velocity. In the case of air registers using high velocity air streams this is done by fitting a tip plate which spills the primary air over into a series of vortices. This ensures good mixing of the air and fuel and, by reducing the forward speeds involved, helps to maintain the primary flame within the refractory quad. Secondary flame:- The larger oil droplets, heated in their passage through the primary flame zone, then vaporize and begin to burn. This, although a rapid process, is not instantaneous, and so it is essential that oxygen is supplied steadily and arranged to mix thoroughly with the burning particles of oil. An essential feature for the stability of this suspended secondary flame is that the forward velocity of the air and oil particles must not exceed the speed of flame propagation. If it does the flame front moves further out into the furnace and the primary flame will now burn outside the gnarl with resulting instability due to overcooling. Careful design of the swirl vanes in the air register can be used to create the required flow patterns in the secondary air stream. The secondary flame gives heat to the surrounding furnace for the generation of steam. Sufficient time must be given for complete combustion to take place before unburnt oil particles can impinge onto tubes or refractory material. This usually entails the supply of a certain amount of air in excess of the theoretical amount required for complete combustion if these practical considerations could be neglected, and unlimited time taken for the mixing of the air and fuel. The actual amount of excess air supplied depends upon a number of factors, such as the design of the furnace, the efficiency of the combustion process for the condition of load, etc., but will in general reduce the boiler efficiency to some extent due to the heat carried away by this excess air leaving the funnel. It can also lead to increased deposits in the uptakes due to the increased amount of sulphur trioxide that will form from sulphur dioxide in the presence of excess oxygen.

Improved high lift safety valve

It is a spring loaded valve. Spring which produces the load is fitted under the cover with a compression nut, so that any degree of compression can be given to suit the pressure to which valve is to be loaded. On top a cap or hood, through which a cotter is passing. It is locked with pad lock so that once surveyor has set the compression it cannot be tempered with. The cotter has a clearance under it equals to 1/4th of the valve diameter, giving the valve sufficient lift to pass the maximum area of the steam escaping. A clearance on the top ensures the valve is bedding on the seat. A clearance between the hood and spindle top is provided more than 1/4th of valve diameter.In this type waste steam assists the main boiler pressure in compressing the spring. Giving the valve more lift. While in a simple spring loaded valve the waste steam pressure acts downward on the valve lid and retard the efficient operation by restricting the valve lift. The loose floating ring surrounds an extension of the bottom spring cover, which carried the spring so forming a gland. The ring is held down by the waste steam acting on the annular area. Any waste steam which does pass the floating ring will escape to the atmosphere through the relief port in the spring casing. Drains are provided so that any condensate form in the spring casing will drain into the valve chest leads to hot well. The valve lid is constructed with a blow down ring of greater diameter. Just above the seat which provide a greater area for the steam pressure to act upon. When valve open from its seat, the steam pressure acts on the extended area causing the valve to pop open. If the valve is allowed to close slowly, the final thin film of the steam blowing across the faces causes feathering condition. Also this steam flow at very high speed cause quick cutting of the faces also called wire drawing of the faces of seat lid or disc. Feathering will result in falling of boiler pressure well below the boiler blow off pressure before the valve finally closes. The shaped valve seat causes the valve seat to pulsate and this dribbling action enables the valve to close clearly and sharply with very little blow off effect. This shaped valve makes a form of lips. The clearance between is called lip clearance. With decrease in lip clearance the amount of blow down increases and vice versa. The width of bearing face of the valve and seat should not exceed 1.6mm. Lip clearance should maintain between 3.2-4.8mm. which depends on the boiler pressure.

Overhauling The following part should be examined during overhauling or survey . Valves or seat maybe marked or warn valve should ground in by means of a jig (since valve lid is wingless) taking care of makers specified clearance. valve wings if fitted must be at least 0.8 mm clear in the seat and must not project below the seat. The seat must be a good fit and securely held by set pins. Inside of chest must be free from corrosion and any scale adhering removed. drain should be examined to see that it is clear. the spring should be hammer tested to make sure that it is not fractured and inspected for corrosion. The spring should length should be tested against a new spare. the end of coil should be good fit in the recessed collar. The valve spindle should be hammer tested ensure it is not cracked and check for alignment. Clearance between the top of the cottor and top of the slot in the spindle to be checked after grinding a safety valve. All bushes must be secured in the housing and have sufficient clearance. Compression screw should be checked for tightness on the threads. The easing gear must be checked to see that it is in good order. After carrying out above inspection and adjustments the parts are assembled and valve made ready for setting to the required. reset after an overhaul. Pressure setting of safety valve: Boiler safety valves are set to the required pressure using a standard tested certified pressure gauge as to its accuracy. A surveyor is present to see the test and issue certificate. Block one safety valve by gagging tool with little wrist tight. Ignite the burner and increase pressure with low flame until non block safety valve blow off. Shut the burner immediately adjust the blow off pressure and repeat until correct blow off pressure obtained. Adjust the second safety valve as described above. Setting tolerance of +/- 3% allowed by classification society. The compression ring is then machined and fitted in place and locked by Surveyor seal.

A. Describe, with aid of a Sketch the safety valves for an auxiliary boiler.

Valve lift: - Applicable for the flat or mitered face 45° valve. Area of valve bore = area of escape i.e the valve circumference X lift; Neglecting area taken by the valve prongs. To give greater lift than D/4, is unnecessary, this gives the full equivalent area. Excessive lift results in shock or hammering thus the fatigue will take place. Also fracture can take place because of flattering if the lift is excess. the lift of improved high lift safety valve is D/12, while it is D/24 for high lift and D/36 for ordinary safety valve. Blow down of a safety valve is the difference between lifting pressure and seating pressure. Improved high lift safety valve:- It is a spring loaded valve. Spring which produces the load is fitted under the cover with a compression nut, so that any degree of compression can be given to suit the pressure to which valve is to be loaded. On top a cap or hood, through which a cotter is passing. It is locked with pad lock so that once surveyor has set the compression it cannot be tempered with. The cotter has a clearance under it equals to 1/4th of the valve diameter, giving the valve sufficient lift to pass the maximum area of the steam escaping.

A clearance on the top ensures the valve is bedding on the seat. A clearance between the hood and spindle top is provided more than 1/4th of valve diameter. In this type waste steam assists the main boiler pressure in compressing the spring. Giving the valve more lift. While in a simple spring loaded valve the waste steam pressure acts downward on the valve lid and retard the efficient operation by restricting the valve lift. The loose floating ring surrounds an extension of the bottom spring cover, which carried the spring so forming a gland. The ring is held down by the waste steam acting on the annular area. Any waste steam which does pass the floating ring will escape to the atmosphere through the relief port in the spring casing. Drains are provided so that any condensate form in the spring casing will drain into the valve chest leads to hot well. The valve lid is constructed with a blow down ring of greater diameter. Just above the seat which provide a greater area for the steam pressure to act upon. When valve open from its seat, the steam pressure acts on the extended area causing the valve to pop open. If the valve is allowed to close slowly, the final thin film of the steam blowing across the faces causes feathering condition. Also this steam flow at very high speed cause quick cutting of the faces also called wire drawing of the faces of seat lid or disc. Feathering will result in falling of boiler pressure well below the boiler blow off pressure before the valve finally closes. The shaped valve seat causes the valve seat to pulsate and this dribbling action enables the valve to close clearly and sharply with very little blow off effect. This shaped valve makes a form of lips. The clearance between is called lip clearance. With decrease in lip clearance the amount of blow down increases and vice versa. The width of bearing face of the valve and seat should not exceed 1.6mm. Lip clearance should maintain between 3.2-4.8mm. which de[pends on the boiler pressure.

B. Identify, with reasons, the part that require particularly close attention during overhaul; Overhauling The following part should be examined during overhauling or survey . Valves or seat maybe marked or warn valve should ground in by means of a jig (since valve lid is wingless) taking care of makers specified clearance. valve wings if fitted must be at least 0.8 mm clear in the seat and must not project below the seat. The seat must be a good fit and securely held by set pins. Inside of chest must be free from corrosion and any scale adhering removed. drain should be examined to see that it is clear. the spring should be hammer tested to make sure that it is not fractured and inspected for corrosion. The spring should length should be tested against a new spare. the end of coil should be good fit in the recessed collar. the valve spindle should be hammer tested ensure it is not cracked and check for alignment. clearance between the top of the cottor and top of the slot in the spindle to be checked after grinding a safety valve. All bushes must be secured in the housing and have sufficient clearance. compression screw should be checked for tightness on the threads. The easing gear must be checked to see that it is in good order. After carrying out above inspection and adjustments the parts are assembled and valve made ready for setting to the required.

C. Describe how the safety valves are reset after an overhaul. pressure setting of safety valve: Boiler safety valves are set to the required pressure using a standard tested certified pressure gauge as to its accuracy. A surveyor is is present to see the test and issue certificate. Block one safety valve by gagging tool with little wrist tight. Ignite the burner and increase pressure with low flame until non block safety valve blow off. Shut the burner immediately adjust the blow off pressure and repeat until correct blow off pressure obtained. adjust the second safety valve as described above setting tolerance of +/- 3% allowed by classification society. The compression ring is then machined and fitted in place and locked by Surveyor seal.

Leaky Economiser at sea

In the event of failure of economizer tubes the water consumption in the boiler will increase drastically, also white smoke can be seen at the funnel outlet. An exhaust gas by pass if provided then it can be used and the job of repair can be planned for the next port of call. Generally by pass of exhaust gas for the economizer is not fitted and in this case the repair has to be carried out at earliest.

The aluminum fins fitted to the economizer have a relatively low melting point and, therefore, must not be overheated. If there is no circulation of water through the economizer the heat collected from the exhaust gases will not be carried away by the water. This heat will then build up in the tubes and fins to the point where the fins will melt down.
1. Inform the bridge, take control to local and raise the engineers call alarm.
2. Keep the boiler water in circulation though economizer and keep topping up the hot well.
3. Reduce the load and stop the main engine as the sea conditions permit.
4. Open the turbo charger drain. Keep the circulation pump running for an ample period.
5. After stopping the circulation the boiler has to be isolated from its feed and supply. Also isolate electrically. For that isolate from the main circuit breaker, put tag "Man at work". Close Main steam stop valve and Feed check valve of the the boiler. Close the fuel inlet valve to the burner. Open the vent valve & wait for the pressure to fall to atmospheric pressure.
6. Open the top Man hole inspection door first and then the bottom one. if the leaky tube can be identify. Other wise Circulating water has to be supplied to find the leaky tube. Mark the leaky tube. Close and isolate the water circulation system.
7. As a temporary repair the tubes can be blanked at both the ends of tubes from inside of the headers. For this purpose manufacturer supply the brass or steel tapper plugs.
8. Again check for any leakage after blanking off the tubes and if found intact then the economizer can now be put to normal service. Start the main engine and increase load gradually by giving close attention to the color of exhaust gas at funnel outlet and water consumption.
9. If the total blanked tubes has reached to 20% of the total tubes, then renewal of the tubes has to be planned and this should be carried out by a certified person in the presence of surveyor.

ECONOMIZER:- it is a boiler which utilizes the waste heat of exhaust gas to generate steam. The water is circulated in the tubes laying in the path of exhaust, by means of boiler circulating water pump, taking suction from the main boiler drum, with the heated boiler water/steam returning to the steam drum.
The economizer is a feed water heater. It is composed of sixty-two 2-inch U-tubes. Before entering the boiler the feed water flows through a myriad of passes through these 2-inch tubes, finally discharging into the boiler steam drum. Exhaust gases from the furnace of the boiler pass around these tubes and, in passing, transmit a portion of their heat through the tubes into the feed water. A series of aluminum fins is attached to the economizer tubes. These aluminum fins furnish an extended surface for the transfer of heat. The rise in temperature of the water in its passage through the economizer is approximately 100 degrees F. which means that water leaving the de-aerating tank at 240 degrees F. will enter the boiler at approximately 340 degrees F. This does away with the necessity for any feed heater in the system. The aluminum fins fitted to the economizer have a relatively low melting point and, therefore, must not be overheated. If there is no circulation of water through the economizer the heat collected from the exhaust gases will not be carried away by the water. This heat will then build up in the tubes and fins to the point where the fins will melt down. If the fins should melt, a baffle will be formed in the boiler uptake which may well be the cause of a flare-back into the fire room. Therefore, while steaming the feeding of water into the steam drum should never be stopped completely, as this will stop the circulation of water through the economizer. If the water level becomes so high that this may appear to become necessary, it is far more advisable to blow the boiler down to reduce the water level than to shut off the feed water. When lighting off it is of course impossible to feed until the boiler is put on the line. To protect the economizer in this case no more than two burners, with the port-use sprayer plates, should be used to bring up the pressure. If any work has been done in the uptake of the boiler, it is desirable that an inspection of the economizer top be made before lighting off the boiler, since some piece of metal may have been left resting in contact with the fins of the economizer. Should this be the case, the point of contact would be a point of concentrated heat which would cause the fins to overheat.

Gas side of Boiler

Combustion is the burning of fuel in air, in order to generate heat energy. For complete and efficient combustion the correct quantities of fuel and air must be supplied to the furnace and ignited. About 14 times as much air as fuel is required for complete combustion. The air and fuel must be intimately mixed and a small percentage of excess air is usually supplied to ensure that all the fuel is burnt. When the air supply is insufficient incomplete combustion the result is black smoke and soot formation. The fuel must be break up into very tiny particles known as atomising to mix with the air to make a homogeneous explosive mixture. The atomisation of fuel is done with the help of burners which are of different types. The atomisation of fuel is achieved by forcing the under pressure oil through an orifice at the end of the burner the pressure energy in the fuel is converted to velocity. Spin is given to the fuel prior to the orifice, imparting centrifugal force on the spray of the fuel, causing it to atomise.
1) Air supply- The flow of air through a boiler furnace is known as draught. Marine boilers are arranged for forced draught, means fans which forces the air through the furnace. The mixing of air and atomised fuel is carried out with the help of a air register. The register is generally based on a circle or hexagon with the burner mounted axially at the centre. Air register employing pressure atomiser, consists of two principle parts. The diffuser and the air foils (vanes). Use of two streams the primary air through the diffuser and the secondary through the air vanes. The air is given an angular rotation (swirl) by vanes, on its way to the furnace, in order to assist in mixing the air and oil. The diffuser institute the primary mixing of the droplets with air and prevents blowing off the flame from the atomiser the air vanes guide the major quantity of air to mix with oil particles after they leave the diffuser and to envelope the flame. The construction of diffuser, air vanes and register's door is such, that oil and air are given a clockwise motion.
2) Fuel oil- Marine boilers currently burn residual low grade fuels. This fuel is stored in D.B tanks from which it is drawn by a transfer pump to settling tanks which is being heated with the help of steam coils provided inside here any water in the fuel may be settle out and water can be drained off. Before or just after receiving the bunker fuel, various chemicals according to the grade and quality is added in a calculated measured amount to disperse sludge, suspended particles (catalytic fines or cat fines) known as fuel oil treatment (FOT) chemicals. Fine mesh filters are in suction line before the pump, to collect the sludge and solids particles, enquired to clean preferably before every pump operation. The oil from the settling tank is filtered and purified through a purifier if the grade is such that cat fines are more, out of two purifiers one to be used as purifier, the other as clarifier in parallel and stored in a service tanks provided with steam heating coils. The temperature is maintained around 75-80 deg cel. From there the oil is pumped to a heater through a fine filter. Heating the oil reduces the viscosity and makes it easier to pump and filter. Care must be taken for heating up, must be carefully controlled to avoid gassing of the pump or cracking or breakdown of fuel. A supply of light oil is available for initial operation or continuous use, from the fine filter the oil passes to the burner.
3) Unburnt fuel particles or the residual carbon particles will accumulate on its way along with the flue through the uptake trunking at places, known as soot. Soot is a very dangerous problem, not only it is hindering the heat transfer but can catch fire in suitable conditions which are omnipresent in that environment. The thin layer of soot will decrease the thermal and fuel efficiencies. It is better to disperse the soot by using steam jets. This operation is carried out with the help of soot blowers, soot blowers are the equipment which is fitted at different position in the uptake and coils. The appliance is consist of a long hollow shaft, closed at one end and number of holes are provided at one fourth of the peripheral surface all along. The shaft is opened at one end and connected with a wheel and worm. The shaft can rotate along it axis. The shaft is connected with a steam line through stuffing box and gland. When the steam valve is opened the steam will come through the holes as jets and clean up the loose soot which will go away with the flue. The operation should be carried out after informing bridge to check out the wind direction. The EGE or auxiliary boiler must on full steaming condition. But never use when there is an uptake fire.

Re-commissioning of Boiler

As per company's instruction the EGE to be re-commissioned again. As you are new you may not be knowing the past fact and history, the reason why it was taken out of service on whose instruction. for that you have to go through the old records and log sheets. If it was taken out of service due to some problem whether it had been attended and rectified. Other wise you have to follow the under mentioned criteria. Before taking any action to recommision it, the followings to be kept in mind. Check the manuals and any special instruction. From manuals ensure the type, construction and special features if any. Check and arrange for the tools and implements required. Through c/e obtain a work permission. Be sure about the idle time available. if vessel is in port get a immobilisation request from the authority as main engine can not be operational select your team members. If every thing is in order then proceed.

Causes for ceasing work might be attributed to
1) Defective circulating pump.( not building up pressure, excessive leakage or ceased). check and rectify.
2) Check the pipe lines for any leakages, leaky joints or blockage. rectify or replace if necessary.
3) Check all line valves for proper operation, over haul
4) Open the casing cover, visual checking of the coils, clean and wash.
5) Check soot blowers for proper operation.
6) If control flap is provided for controlling the exhaust to the coils or bypassing it to atmosphere. check the flap condition, easy movement and total sealing on either openings. repair, ease up.
7) Check the number of generating coils, whether they are individually connected with valves with inlet and outlet manifold. If individual then test the coils for leakage by opening the inlet valve of the coils and keeping shut all other valves, start the circulating pump manually keeping an eye on the discharge pressure just check at 5 kg pressure (be careful, nobody should be near vicinity and keeping the drain open) or by connecting a manual pump. Check all the coils, if any one is leaking can be isolated by keeping the valve shut and blanking both the valves.(if it is a smoke tube type. The leaky tube to be plugged with metal plugs and to be welded, if found in order try it out with circulating pump just gaging the safety valves. If found in order fit back the covers. After some time just ease up the safety valves and check if any entrapped water or steam is there. if not. take out both the safety valves (fitted on a common chest), mark as per their position (F-A or P-S). Dismantle and check the valve lid, seat, spindle, spring carrier, spring adjusting screw, cotters, releasing lever. Overhaul and boxed back, but can not be adjusted till the main engine operates. When the vessel sails out, after receiving full away, start setting the safety valves (must be done by chief engineer with minimum 3 years sailing experience) set with a calibrated pressure gauge.
After everything over sent a report to office and to the class stating vessel name, IMO No., position of the vessel ( lat. long. with GMT time and date ), set pressue, chief engineer's COC no and grade.

Stresses in boiler

Consider a thin cylindrical shell subjected to an internal pressure. This sets up stresses in the circumferential and longitudinal axes which can be calculated as follows: Circumferential stress: If pressure acting upon the circumference is resolved into horizontal components. the resulting horizontal force = pleasure x projected area. This is resisted by the stresses setup in the longitudinal joint. Then for equilibrium conditions: Horizontal forces to left = Horizontal forces to right Horizontal forces to left = Resisting force in longitudinal joint Pressure x projected area = Stress x cross sect. area of joint Press. x dia. x lengths = Stress x 2 x thickness x length Pressure x diameter / 2 x thickness = Stress in longitudinal joint Longitudinal stress The force acting upon the end plate is resisted by the dress set up in the circumferential joint. Then for equilibrium conditions. Horizontal forces to left = Horizontal force to right Pressure x end plate area = Resisting force in circumferential joint. Pressure x (π/4) x diameter2 = stress x cross sect. area of joint Pressure x diameter /4 x thickness = Stress in circumferential joint Thus it follows. that longitudinal joint stress is twice the circumferential joint stress. Then rearranging the shell formula in terms of pressure Max press=max stress x 2 x thickness /diameter This pressure will be reduced by the efficiency of the joint subjected to the greatest stress Max working pressure = max stress x 2 x thickness x joint efficiency /diameter It has been shown that the joint subjected to the greatest stress will longitudinal joint; the strength of joint therefore governs the allowable working pressure, and so the strongest type of riveted joint used in the boiler, is used for this joint. Any material cut from the shell will weaken it by an extent related to the amount cut out. In general any holes cut in the shell, with a diameter greater than:-2.5 x plate thickness + 70 mm must be provided with compensation for the loss of strength due to the material cut out. The largest holes cut in the shell include the manholes, and where these are cut in the cylindrical portion of the shell they must be arranged with their minor axis parallel to the longitudinal axis of the boiler. This is due to the stress acting upon the longitudinal seam being twice that acting upon the circumferential seam. Thus the shell must not be weakened more than necessary along its longitudinal axis. Stress = Pressure x diameter / 2 x plate thickness Thus, it can be seen that if the stress in the material is to be kept within fixed limits (as is the case with boiler material) then, if the Thickness pressure or diameter increases, the plate thickness must also change if the ratio is to remain constant. Therefore, if boiler pressure is increased, either the boiler shell diameter must decrease, or the boiler scantlings increase; the latter leading to increased cost and weight. In order to accommodate the combustion chamber, smoke tubes, etc., no great reduction in the shell diameter of tank type boilers is possible, and thus very thick shell plates would be required for high pressure. The furnace must also be considered, as its thickness must be kept within certain limits to prevent overheating. However, its diameter cannot be reduced too much, otherwise difficulties in burning the fuel in the furnace would arise. For these reasons the maximum pressure in tank type boilers is limited to about 1750 kN/m2. When a force is applied to a curved plate, internal forces are set up which enable the plate to withstand the force without undue distortion. The bursting stress can be resolved into perpendicular components, one of which will oppose the force. The surface will bend until this component balances the pressure. It will then be found that the surface is in the form of an arc of a circle. When the pressure acts upon a flat plate, it will tend to bend the plate until equilibrium is obtained. Thus to prevent undue distortion the flat. Plate must be very thick or supported by some form of stay. It follows that if the use of flat surfaces can be avoided in the design of a pressure vessel there will be no need to fit internal stays. Thus pressure vessels are often given hemispherical ends but, if this is not possible, any flat surfaces must be stayed or of sufficient thickness to resist the pressure without undue distortion. The Department of Trade and the classification societies, such as Lloyds, have very strict rules governing the dimensions and materials used in the construction of pressure vessels, so that they can withstand the forces set up by pressure and thermal effects. The DOT require that carbon steel used in the construction of pressure vessels is to be manufactured by open hearth, electric, or pneumatic processes such as LD, Kaldo, etc. These may be acid or basic in nature. To ensure the materials used are of uniform quality within the requirements laid down, tests are carried out on samples of material. Some of the materials are as follows: Shell plates for riveted construction, and steam space stays are to have a tensile strength between 430-560 MN/m2, with a percentage elongation of not less than 20 per cent on a standard test length. In the case of shell plates for welded construction the strength requirements lie between 400-450 MN/m2. Plates which have to be flanged have lower strength requirements, but must have greater elongation; therefore, the tensile strength of these plates should lie between 400-460 MN/m2, with a percentage elongation of 23 per cent on a standard length. Similar requirements are laid down for plates, other than shell plates, which are to be welded, also for plates used in the construction of combustion chambers, and the material used for combustion chamber stays. To maintain control over the final product the following tests are carried out: Tensile test For this standard test pieces are prepared from samples of material; these are then placed in a tensile test machine and loaded to the required values. This enables both the tensile strength and the percentage elongation of the material to be determined. Bend test In this test a prepared test piece is bent cold either by hydraulic or other pressure, or by repeated hammer blows. Test on Rivet bars:- In addition to the tensile and bend tests described, are also subjected to dump testing and sulphur printing. In the latter, tests are carried out on a cross section of the bar to prove there are no sulphur segregates present in the core. In dump testing short lengths, equal to twice the diameter of the bar, are cut from the bar and compressed to half their original length without signs of fracture. Finally the following tests are carried out on a few completed rivets, selected at random from each batch. The rivet shank must be bent cold until the two parts touch, without any signs of fracture at the outside of the bend. In the other, the rivet head is flattened until its diameter is equal to 2.5 x original diameter, with no sign of cracking at the edges.

Boiler accumulation pressure test

A boiler test to ensure that the safety valves can release steam fast enough to prevent the pressure from rising by 10%. The main steam stop valve is closed during the test. Accumulation test of boiler safety valves to relieve the boiler off all the steam they are capable of generating when fired to full capacity.

In this test, all steam outlets from the boiler, except such as may be necessary to operate the boiler, are shut off.

The fire is then forced to maximum capacity for a period of 15 minutes for fire tube boilers and 7 minutes for water tube boilers.

During the test, the steam pressure must not exceed 10% above the maximum allowable working pressure.

It is a classification society requirement that when initially installed, accumulation tests are to be carried out on the safety valves of boilers. During such tests, which are affected with the steam stop valves shut, and under full firing; conditions for 15 minutes in the

case of tank boilers, and 7 minutes in the case of water tube boilers, the accumulation of pressure is not to exceed 10% of the working pressure.

Accumulation tests are sometimes waived with water tube boilers when such a test would endanger the superheaters, and in such cases, consideration is given to calculations and previous experience of the actual capacity of the safety valves in question.

Q. Boiler accumulation pressure test?
Q. List of chemicals used in boiler?
Q. What is coagulant ratio & its significance?
Q. Reasons of boiler burner backfire & remedies?
Q. Boiler contaminants?
Q. Boiler hydraulic test and safeties?
Q. Boiler water scale formation?
Q. Non alkaline salt, treatment for non alkaline salt?
Q. Excess phosphate reserve consequences?
Q. Caustic embrittlement?
Q. Boiler water salts and treatments?
Q. D type boiler, two-stage superheater location and use?
Q. Arrangements to prevent ingress of oil in boiler feed water system?
Q. Swell and surge in boiler. What arrangements in control system to prevent it? Q. Explain pressure for setting of boiler safety valves?
Q. DP cell of boiler draw and explain. How is the difference pressure is maintain? Q. Boiler safety valve? How the stem is connected to the seat?
Q. Boiler tubes arrangements in order to avoid thermal crack?
Q. How boiler blowdown valve is fitted on ship side?
Q. Oil in boiler. Actions?
Q. Boiler water level controller?
Q. Boiler flame failure reason & action?
Q. Instructions to 5E regarding boiler blow down?
Q. Boiler preservation?
Q. How will u know boiler firing at full load?
Q. Exhaust gas recirculation system for boiler?
Q. Auto starting sequence of boiler?
Q. Boiler cold starting?
Q. Corrosion in boiler and how to prevent it?
Q. Oil in boiler gauge glass reason and your action?
Q. Name all salts in boiler water and explain function of each.
Q. Boiler hardness and non hardness salts?
Q. Boiler tube is leaking, action, how will you come to know about the leak how to rectify?
Q. Oil has entered the hot well how will you come to know and action?
Q. Boiler safety valve overhaul?
Q. Arrangement for allowing tube expansion and contraction?
Q. How improved high lift can be achieved in boiler safety valve?
Q. Why floating ring not fixed ring?
Q. Why boiler outer drum is circular in shape. How controlling the water level?
Q. Boiler full lift safety valve, construction and working principle?
Q. Why the lift cannot be more than D/4?
Q. Boiler safety valve all components and materials of all the components?
Q. Enlist all boiler water test, chemicals incorporated and purpose of that chemical?
Q. Phosphate reserve purpose, value in ppm and its end product precipitated or dissolved?
Q. Trunk type boiler, why it's end is curved?
Q. Boiler uptake fire indication, reason?
Q. Boiler raising from cold?
Q. Why do we carry out boiler water test, what are coagulant?
Q. Advantage of water tube boiler?
Q. How boiler is rated and your boiler rating onboard ship?
Q. What are wall tubes boilers?
Q. Propose of vent valve in boiler?
Q. Boiler combustion methodology and combustion components?
Q. Boiler refractory damaged, reasons?
Q. What is CSM survey? Is boiler safety valve survey is carried out along with CSM?
Q. Boiler level testing methods while boiler in operation?

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Boiler water Treatment

Burners

Preservation of boiler

Steam from cold condition

Boiler and feed water troubles

Preparing boiler for survey

Boiler tube failure and repair

Superheater tube arrangement

Plan to reduce uptake fire

Corrosion protection of steam line

Combustion process

Improved high lift safety valve

Leaky Economiser at sea

Gas side of Boiler

Re-commissioning of Boiler

Stresses in boiler

Boiler accumulation pressure test

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