Marine Engineering Study Materials

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.

 

 Reference:

Oral Guide by – MIN ZAR TAR