Marine Boiler's

What is the meaning of marine boilers?

Boiler is a pressure vessel used on ships in which the water is heated to evaporate and generate the steam and the unit is so arranged that the generated steam accumulated in it. The two main types are water tube and fire tube.

What is the boiler mounting?

It is directly fitted to the boiler shell. They are:

1.       Safety valve

2.       Main steam stop valve

3.       Air vent cock

4.       Two gauge glass level indicators

5.       Feed check valve

6.       Scum blow down valve

7.       Bottom blow down valve

8.       Salinity cock or test cock

9.       Man hole doors.

Where are air vent cock located and its purpose?

The air vent cock is fitted at the top of the steam space of the boiler.

Its purpose are-

1.       To release air from the boiler either filling the boiler water or raising the steam.

2.       To allow air to enter in the event of boiler cooling down or blowing down. ( to prevent vacuum effect)

What are the safety arrangements in marine boiler?

1.       Safety valve

2.       Low / high water level alarm

3.       Too low water level alarm and shut down

4.       Water level indicators

5.       Pressure gauge

6.       Low fuel oil pressure alarm

7.       Low / high fuel oil temperature alarm

8.       Flame failure alarm

9.       Smoke density alarm

10.   Easy gear arrangement

11.   Air vent

12.   Force draught fan stop alarm

13.   Low / high steam pressure alarm

Why need to blow down the gauge glass?

Gauge glass blow down is made to know the boiler and gauge glass connection is clear or not and to give the exact water level in the boiler.

 Boiler gauge glass blow through procedure?

1.       Shut steam and water cocks than open the drain cock.

2.       After draining water from the sight glass, there is nothing come out, both steam and water cocks are good in order.

3.       Open the steam cock side, blow out the steam.

4.       Close the steam cock side, the steam connection is clear.

5.       Open the water cock side, blow out the water.

6.       Close the water cock side, the water connection is clear.

7.       Close the drain cock.

8.       Open the water cock, water should then gradually come rise up to the top of the gauge   glass.

9.       Open the steam cock, the water in the glass should fall to the level of the water in the boiler.

Why need to blow down the boiler water?

§  Boiler blow down is made to reduce the density of salt and to remove the dissolved and suspended solids, also the floating solid impurities in the boiler system.

§  If there are not removed from the boiler water system, foaming, priming, corrosion will occur in the boiler steam space and feed water system.

§  See ‘Boiler Blow Down’.

Why scum blow down or surface blow down is carried out ?

§  To remove accumulated, suspended and floating solids, impurities and also remove dissolved solid concentration, they hinder the formation of steam.

Why bottom blow down is carried out ?

§  To remove suspended solids and residual sludge that have settled at the bottom.

§  If these contaminants are not removed regularly they will build up until they hinder the circulation patterns.

What is the purpose of boiler water test ?

§  To ensure that proper chemical treatment are maintained at all time.

§  To detect the present of contaminants in the water that may be injurious to boiler and system.

Enumerate the boiler water test ?

1.       Alkalinity test [Phenolphthalein ( p) alkalinity test, Total ( T ) alkalinity test (2 x P)]

2.       Chloride test

3.       Condensate PH test

4.       Amerzine test ( Hydrazine test )

5.       Excess phosphate test

6.       Conductivity test (Total dissolve solids  test)

7.       Hardness test

Alkalinity test

§  This is to ensure that the boiler water prevent corrosion by neutralization of acidic gases.

(a)  Phenolphthalein or ‘p’ alkalinity

§  This test is carried out to prevent acidic corrosion

§  To test for presence of all of the hydroxide, one half of the carbonate and one third of phosphate present in a water sample.

(b)  Total ( T ) alkalinity test

§  To determine the amount all of hydroxide, all of the carbonate, and two thirds of the phosphates

Note:   Hydroxides and carbonates can co-exist together in a solution but hydroxides and bi-carbonates cannot. 

Chloride test

§  To know the amount of salt in boiler water.

§  To minimize chloride level and to adjust the blow down.

Condensate PH test

§  To control condensate PH value within a limit.

§  To minimize corrosion in steam and condensate system.

Amerzine test ( Hydrazine test )

§  To test for dissolved Oxygen content

§  To know reserve hydrazine (N2H4 ) ppm and to prevent corrosion and aeration.

§  To minimize oxygen pitting and corrosion in boiler, steam and condensate system.

 Phosphate test

§  To control the scale formation due to hardness (presence of Phosphate in sample means no hardness salts)

§  A reserve of phosphate should be maintained in the boiler water ready to neutralize any hardness salts which may enter.

 Conductivity test

§  Measure of the total amount of dissolved solids (T.D.S) including the treatment chemicals. (Excessive density leads to priming and or deposits)

§  To remove dissolved and suspended solid by blowing down.

Hardness test

§  To check for salt causing “hardness”

Note: Hardness test of boiler water are not necessary when the phosphate is above the lower limit of the control range.

What are the advantages of boiler water treatment ?

1.       To prevent the scale formation in the boiler and feed system

2.       To prevent corrosion in boiler and feed system.

3.       To control the sludge formation and prevention of carry over with the steam.

4.       To maintain the boiler water in alkaline condition and free from dissolved gases.

5.       To prevent of entry into the boiler of foreign matter such as oil, waste, mill scale, FeO, Cu, Sand, etc.

What are the types of boiler by pressure ?

1.       Low pressure boiler  –  up to 10Kg / Cm2

2.       Medium pressure boiler  –   10-25 Kg /Cm2

3.       High pressure boiler  –  Over 25 Kg / Cm2

What is water hammering and how will you prevent it ?

§  It is the impact of moving water in steam line when the steam is allowed to enter a line with condensed water.

§  The steam will condenses and partial vacuum occurred and move back the water the along the pipe with very high velocity, and the water will strike at the vent or valves.

To prevent the water hummer –

1.       Install steam trap in the line

2.       Open the drain first before allowing the steam into the line.

3.       Crack open of steam valve at first.

How to make boiler water test on your ship ?

The boiler test is carried out as follows.

1.       Firstly take the boiler water sample from the salinometer cock or test cock and cool down.

2.       The test is carried out by the using maker’s supply test kit, chemicals, instruments and instructions.

How do you take boiler water sample ?

§  Slowly open the salinometer cock until clean hot water coming out.

§  Then collect the boiler sample with copper jar.

How to know scum blow down valve open or not ?

§  It can be check by opening of ship side blow down valve. Banging noise will appear, scum blow down valve is in open position.

§  It can also detect, over heating of scum blow down pipe.

Where is manhole doors fitted ?

§  They are fitted at one at steam side and other one for water side.

Effect of foaming and priming ?

1.       Can cause water hummer

2.       Can cause contamination and scaling.

3.       Can cause fluctuation of working water level.

What is boiler blow back ?

§  It occurs when lighting up with explosive gas and oil droplet (Oil residue) inside the furnace without pre-purging sufficiently.

§  The ignition results in a large flue gas inside the furnace and these gases blow out with increase high pressure through the furnace opening.

Procedure for hydraulic pressure test on marine boilers ?

Hydraulic pressure test is 1.25 times working pressure, ( 10 minutes maintain )

1.       Close all openings.

2.       Open air vent cock.

3.       Fill up boiler water fully

4.       Close the air vent cock

5.       Place hydraulic jack to feed water line.

6.       Fit standard pressure gauge.

7.       Applied hydraulic pressure 1.25 times of working pressure and maintain 10minutes.

What is liquid coagulant in marine boilers ?

§  It has more molecular weight, colorless solution, containing sodium aluminates, starch, terming, and resin.

§  Once being dose into the boiler water floating solid particles and suspended solid are settled to the bottom of the boiler and easily remove by blowing down.

How to renew the boiler gauge glass ?

1.       Shut steam and water cocks and open drain cock.

2.       Check any leakage from the respective cock.

3.       Slacken the gland nuts.

4.       Open the cap and remove gauge glass.

5.       Fit new gauge glass, correct size and length into its space.

6.       Give the expansion allowance 1/8 in vertical clearance.

7.       Use new packing.

8.       Close the cap.

9.       After fitting, warm the glass by steam.

10.   Tighten the gland nut.

11.   Then steam and water pressure should be tested whether they are fair and clear.

12.   Close the drain and open the water and steam side cocks.

13.   Check the leakage; all are satisfactory put back into operation.

Routine boiler maintenance carried out on ships ?

1.       Clean the rotating cup.

2.       Check and adjust the belt tension between motor and rotating shaft.

3.       Clear the pilot burner nozzle and fitter.

4.       Clean carbon deposit on electrodes ( igniter ) and adjust the gap.

5.       Check the fuel valve and air register linkages and joints.

6.       Check and clean the flame eye cover glass.

7.       Check and clean inspection peep hole glass cover.

8.       Clean fuel oil fitter.

9.       Check the fuel oil pressure.

When boiler safety valve setting made ?

§  Every boiler survey.

§  After safety valve overhaul.

Why ship side blow down valve is open first and close last ?

§  To prevent pressure build up in blow down line.

§  In pipe burst, it may be injurious to watch keeper.

What if no test and treatments is done to boiler ?

§  Reduction in boiler efficiency due to poor heat transfer

§  Reduction in tensile strength

§  Reduction in factor of safety

§  Overheating of metal resulting distortion and eventual failure

§  Increase in fuel consumption

§  Excess concentration of NaOH (caustic soda) may cause caustic embrittlement on boiler metal and tend to failure of boiler metal

§  Corrosion

§  Scale formation

§  Foaming, Priming, carry over (due to increase T.D.S level, foaming is present and tend to carried over and priming)

How to control steam pressure in exhaust gas boilers ?

1.       By regulating the amount of gas flowing over the extended surface, i.e. by damper regulation.

2.       By dividing the unit into sections so that each section is controlled by an inlet valve.

3.       By passing steam through an automatic pressure controlled surplus valve to a dump condenser.

4.       By a system designed for a higher pressure than that it is to operate.

What is meant by soot blow ?

§  Purpose is to remove soot, to prevent EGE fire or soot fire.

§  To get steam generating efficiency good

§  To increase heat transfer efficiency

§  Time – Day time at sea  2 -3 times/day

What is the procedure to soot blow ?

1.       Inform to bridge

2.       Check wind direction, good if transverse direction

3.       Raise boiler pressure

4.       Open drain cock until soot blow pipe drain clear

5.       Open soot blower valve

6.       Increase the air to boiler to more than 50 %

7.       Open steam valve & carried out by turning wheel 20 -30 sec

8.       Then close steam valve, soot blower valve 

9.       Open drain valve

Boiler safety valve examination and attention during overhauling ?

§  Checked its valve and valve seat for wear, cavity corrosion and any fault.

§  They should be grounded properly but maker’s limit must be maintained such as width of seating, clearance between valve lip and seat.

§  Valve chest must be cleaned condition and drain line clear.

§  The spring should be hammer tested for any fracture and check for corrosion. Free length is limited to 0.5 % of original free length.

§  The spindle should be hammer tested for any crack and its straightness.

§  The guide plates and bushes are checked for uneven wear and have sufficient clearance to allow free movement of spindle.

§  The compression nut and cover bush’s threads are carefully checked it for any sign of wear and tear.

§  The easing gear should be checked in good order including bearings, cable pulley, and connecting links.

§  Connecting pin should be a free fit in the lid and pin should not bent or pinhole gone out of shape.

§  All safety valves are to be set to operate under steam a little above working pressure not greater than 3% above the approve working pressure of the boiler.

Why safety valve is fitted in two numbers?

§  To make sure that the positive discharging of higher steam pressure from boiler efficiency.

Why fitted in one valve chest?

§  To reduce stress by hole on pressure vessel (boiler)

§  To minimize the numbers of cutting hole on boiler to save it’s strength.

Blowing Down the Boiler on Ships?

The reasons for blowing down the boiler ( both scum and bottom blow down) are to:

1.       Reduce the density of the boiler water by reducing the water level and refilling it with distilled water.

2.       Remove the sediments from boiler water.

3.       Remove oil, grease etc. from top surface of boiler water.

4.       Empty the boiler prior to entry.

5.       Reduce the water level in an emergency.

The scum valve is used to remove floating, foam and oil from the surface of the water.               

Open valves in order (1), (2), (3), and close in reverse. The blow down valve adjacent to the boiler (2) should be fully open to prevent cutting of the valve seating faces. The rate of blow down is controlled by the second blow down valve (3). Never leave the boiler unattended when blowing down and ensure all valves are fully closed after blowing down the boiler. A hot drain pipe indicates a leaking blow down valve. Never open the blow down valves before ship side valve. It result in unwanted pressure build up in the blow down line.