LATEST SAFETY MMD ORAL QUESTIONS & ANSWERS PART-4

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With reference to the safety equipment certificate

(a) Identify the items covered by the certificate which are normally the responsibility of senior engineer.

(b) Describe how the survey of those items should be organized to allow completion with a minimum of trouble and delay.

(c) Explain how it can ensure that the safety equipment is full state of readiness at all times.

(a) Every merchant ship over 500 GT needs a safety equipment certificate.

  • Issued by flag state government, after surveying the vessel according to SOLAS Convention.
  • Validity is every 2 years + 3-month interval.
  • Survey consists of an inspection and demonstration of:
  • Navigation equipment
  • Life safety appliances, Firefighting equipment
  • Vessel documents
  • Safety Devices fitted onboard
  • Following items are normally the responsibility of Senior Engineer.
  • Navigation lights, power sources for Life boat and raft launching area, pilot boarding area, area of muster stations
  • Life boat engine, Emergency fire pump, Emergency air compressor, Emergency battery (24 V), Emergency generator, Emergency steering
  • General alarm, Fire alarm, Engineer alarm, Cold room alarm, all machinery alarms
  • Fire detecting and monitoring system including fixed firefighting installation.
  • Remote quick closing valve, Remote stop switches for F.O and L.O pumps & tanks
  • ventilators, fire dampers, sky light doors and water tight doors

(b) To allow completion of survey with minimum trouble and delay, following process carried out by Senior Engineer.

1. Care of certificate due date

2. Prepare & kept ready necessary cert, test cert, documents, instruction manual concern with the survey.

3. Check and complete C/E log entries for checking, testing and maintenance done for survey items.

4. Operating procedures for L.S.A and F.F.E to be posted where necessary.

5. Ship crew understand and familiar with operations of all safety equipment, practice all crew for demonstration

6. Cleaning Engine room. If any defects were found, rectify in time.

(c) Safety equipment ready and available at all times. At regular intervals, following items checked, tested and maintained to ensure they are in full state of readiness at all times.

Daily – 1. Navigational lights, Bridge and ECR alarm, ship general alarm, engineer alarm

2. Emergency battery Starting battery for emergency generator and its charger

Every week: (as Saturday routine)

1. Test emergency generator, check switch board and earth fault.

2. Test emergency fire pump If it is driven by electric power, check power source from emergency generator.

3. Test emergency steering, and safety failure alarm

4. Test air compressor, practice to start from one GE

5. Test fire detecting, monitoring and alarm system and CO2 alarm

6. Test quick closing valves, remote shut-off switch arrangement for F.O and L.O tanks & pumps

7. Practice to close and open sky-light door, water-tight door and fire dampers.

8. Test OWS 15 ppm alarm and bilge well alarms

9. Test life boat engine, lighting for life boat and lift raft launching area and pilot boarding area.

Monthly- Test main and auxiliary machinery safety devices and alarms, before departure and every month or every voyage and keep good working order.

Annually-

  • Keep clear CO2 pipe lines by blowing with compressor air
  • All fire extinguishers serviced and CO2 bottle weight measured and certificate issued by shore authorized facility.

(a) Explain with an aid of sketches on automatic boiler burning system.

(b) Discuss any two methods of fuel oil atomizer used boiler burner.

(c) What are the safety features that are incorporated within the automatic combustion control?

(a)

  • When steam pressure drops to preset lower limit, the automatic boiler control system is activated.
  • On starting, pre-purging is activated, recirculation solenoid circulates fuel through heater until right temperature is reached.
  • After purging is completed, recirculation solenoid switches over to normal operation
  • At same time, HI/LO flame solenoid switches over to put low flame spill line into operation and ignition is started.
  • Once flame is established, HI/LO flame pressure switch operates HI/LO flame solenoid to change over between high and low flame spill line as pressure varies.
  • When desired steam pressure is reached, the combustion process is terminated by shutting fuel to the burner.

Abnormal conditions which operate the fuel shut off solenoid are:

(i) High and low water level

(ii) High steam pressure

(iii) Flame failure via photocell

(iv) Loss of combustion air

(b) 1. Steam blast jet burner

  • Steam flows along central passage and expanded through a convergent divergent nozzle,
  • Oil sprayed into jet is atomized by this steam. Exit ports arranged to get swirling action.
  • Oil throughput controlled by oil supply pressure.
  • Range of oil pressure is between 1.4 bar to 20 bar, range of steam pressure is between 1.4 bar to 15 bar, TDR is about 20:1

2. Rotating cup burner

  • Oil flows to inner surface of cup through hollow end of spindle.
  • This taper cup is rotated at high speed by means of an electric motor.
  • Oil gets rotating energy and is atomized. Oil throughput is controlled by regulating valve at supply line.
  • The turn down ratio is about 10:1

(c) Safety devices

Alarm

(i) Low and high water level

(ii) Low steam pressure

Alarm and burner shut down

(i) Low fuel pressure

(ii) Low and high fuel temperature

(iii) Air fuel ratio

(iv) Very low and high water level

(v) Draught fan failure

(vi) Flame failure

(vii) High steam pressure

(viii) High flue gas temperature

(a) What is boiler burners’ turn down ratio’?

(b) How many types of boiler burner used in marine boilers?

(c) Explain about one type of boiler burner with aids of sketches.

(a) Boiler burner Turn Down ratio

Turndown ratio (TDR) of a burner = Maximum fuel throughput / Minimum fuel throughput

  • Indicates flexibility of burner to cope up with variations of boiler load without losing efficiency of atomization.
  • In pressure jet burners, square root of the ratio of maximum to minimum oil supply pressures.

(b) Boiler burner used in marine boilers

1. Simple pressure jet burner

2. Spill-type pressure jet burner

3. Variable-orifice-type pressure jet burner

4. Steam blast jet burner

5. Spinning-cup atomizers. (Rotary cup burner)

(c) Rotary or spinning cup burner

Consists of motor driven fan, metering pump and fuel cup.

  • Popular for use with automatic, low pressure boiler plant.
  • Their wide range of TDR, suitable for automatic combustion control.
  • Delivers oil to rear end of expanding cup which rotates at speed of 4000 to 6000 rpm.
  • Oil spread evenly into thin film by centrifugal force over inside surface of cup.
  • Oil on reaching tip of rotating cup by swirly flow of combustion air.
  • complete atomization of fuel delivered. TDR in excess of 15:1.

Main features are

  • Low oil supply pressure.
  • At low throughputs atomization
  • High output possible, up to 3600kg/h

(a) Enumerate the boiler mounting fitted to a low-pressure boiler

(b) State the purpose of each fitting.

(c) State how satisfactory operation of the boiler at all time is ensured.

(a) and (b) 1. Air vent cock – Fitted at the highest point of the boiler to release air when filling water or initially rising steam. Prevent vacuum condition when completely emptying the boiler.

2. Salinometer cock – Fitted to take sample water from the boiler, tested and to determine condition of boiler water.

3. Safety valve – Fitted to protect the boiler over pressure. Open automatically at the preset blow off pressure. Two safety valves are fitted on the single chest.

4. Main steam stop valve – Fitted to supply the steam for general use. It is fitted at the highest point of the boiler. It is non-return valve or screw lift screw down valve.

5. Feed check valve (Two number) – Fitted to give final control over the entry of feed water into the boiler. Non-return valves. One is main valve and the other is auxiliary.

6. Scum valve – Fitted to remove oil or scum and impurities from the water surface of the boiler.

7. Blow down valve – Fitted to remove the scale and other impurities from the bottom of the boiler. Completely empty the boiler by means of this valve when necessary.

8. Pressure gauge – Fitted to show the boiler steam pressure. Two red lines on the dial. Lower line is normal working pressure and upper line is maximum permissible pressure.

9. Water level gauge – Fitted to know the boiler water level. Fitted at either side of the boiler (usually port and starboard). Have steam, water and drain cock

10. Man hole door – Fitted for human access into the boiler for inspection and repair.

(c) The following maintenance should be done to operate the boiler satisfactorily at all time

(1) Gauge glass blow down

  • Done daily to know the correct water level in the boiler and to clear steam line, water line and drain line of gauge glass.

(2) Boiler water test and treatment

  • Boiler water tested daily to know boiler water conditions and to prevent scale formation, sludge formation and corrosion.
  • Boiler water treated with the chemicals to maintain at satisfactory condition.

(3) Scum and bottom blow down

  • Scum blow down is carried out to remove oil and floating impurities from boiler.
  • Bottom blow down carried out to remove deposits impurities from boiler, especially when sea water leaks into boiler water.
  • Function of scum and bottom blow down valves should be checked every week to avoid jamming.

(4) Boiler Feed pumps and Circulation pumps – maintained in good working order.

(5) Safety Valve Easy Gear- tested according to the maker instruction.

(6) Fuel system – Burners, Filter, Air Register maintained in good conditions. Maintenance according to the maker instructions.

(7) All boiler mounting – maintained in good working order at all time.

What are the purposes of boiler water test?

(b) What contaminants contain in boiler water?

(c) Give reasons why even moderately rated Auxiliary boiler required regular attention to both feed and boiler water condition.

(d) Suggest with reason the possible consequence if this attention is neglected.

(a) The purpose of boiler water test

  • To ensure the proper residual treatment chemicals are maintained at all time.
  • To know presence of contaminants in water that damage to boiler.

(b) Contaminants contain in boiler water

(1) Oil contamination: caused by steam heating coil or heater etc leakage

(2) S.W contamination: caused by condenser tube leakage.

  • Other impurities: Boiler feed water contains of salt, O2 and CO2.
  • Corrosion: caused by dissolved gas of O2 and CO2.
  • Scale: caused by Calcium and Magnesium.
  • Foaming, Carry over and Priming: caused by total dissolved solid (TDS) of Sodium chloride and Sulphate salt.

Salts are divided such as

(a) Alkaline hardness salts (Temporary hardness salts)

(b) Non Alkaline hardness salts (Permanent Hardness Salts)

(c) Non-Hardness salt (Common Salts)

(c) Auxiliary boiler requires regular attention to both feed and boiler water condition

  • Oil contamination can cause carry over, foaming priming and acid attacking.
  • Sea water contamination may cause scale, sludge, deposit and acid attacking.
  • Alkaline hardness salts can cause soft scale
  • Non-Alkaline hardness salts can cause hard scale and acid nature.
  • Hardness salts (common salts) are Sodium salt
  • These salts can increase TDS and resulting in foaming, priming, carry over and corrosion.
  • Dissolved gas of O2 and CO2 may also cause the corrosion of the boiler.
  • Corrosion action will waste metal away, reducing overall strength and leading to eventual failure.
  • Auxiliary boiler required regular attention to both feed and boiler water condition.

(d) If regular attention is neglected, the possible consequences are as follows

  • In feed water, Calcium, Magnesium, Sodium salts and dissolved gases of Oxygen and CO2.
  • contaminants of boiler feed water can affect the boiler in form of scale, carryover, foaming, pitting and corrosion.
  • Consequently each contaminant can effect the boiler efficiency, overall strength and leading to eventual failure.

When a steam boiler water tube is started leaking

(a) How do you know?

(b) How will you check the leaking source?

(c) What are the possible leakage sources?

(d) How will you repair the leaked tube?

(e) If case is happening in port and have enough time how you will make a permanent repair with your ship’s crew

(a) How to know

  • Excessive feed water consumption from cascade tank
  • Continuously running boiler feed pump
  • If large amount of leakage, boiler water level low, steam pressure drop & continuous firing of boiler
  • Some water comes out from furnace cover
  • White smoke escaping from boiler uptake

(b) Check Leakage

For water tube boiler (Z boiler)

  • Stop firing and open combustion chamber, leakage can be seen easily.
  • For individually boiler water tube, fill up the boiler water level to full and check. If necessary, pressure test should be done.

For smoke tube boiler

  • Open the smoke side drain valve, water will come out if boiler tube is leaking.
  • After opened up the fireside cover and fill up the boiler water level until all smoke tubes are flooded, we can easily check which one is leaking ligaments.

(c) Possible Sources of water leakage

  • Leakage from tubes
  • Distorted furnace crown plate.
  • Furnace shell plate, opposite to burner opening due to flame impingement.
  • Lower section plate of furnace, due to damage bricks works.

Possible causes of leakage

  • External wastage due to waterside corrosion and pitting caused by using bad quality feed water or improper boiler water treatment.
  • Wastage of the ligaments due to soot blowing with wet steam.
  • Due to local overheating or design fault, unequal thermal expansion between tube and tube plate
  • Due to overheating, deformation or panting tube plate

(d) Remedy and temporary repair at sea(Ref: MIURA Z Boiler)

  • Confirm and identify the leaking water tube.
  • After confirmed, remove castable until its swaged section is exposed so that the stopper can be welded.
  • Cut off one side of the leaking tube by gas.
  • Insert stoppers upward and downward through the cut-off section and seal them all around by welding.
  • Fit anchors on the inside face of the water tube and apply castable .
  • follow the manufacturer’s instructions.
  • This method is only for temporary damage control and the damaged water tube replaced as soon as possible

(e) Procedure for permanent repair in port

  • If happening in port and enough time and spares, repaired permanently by renewal of leaking tube with ship’s crew or available labor.
  • After cool down, inspection of leakage and opening up for renewal of tubes,
  • Cut both ends of leaking tube about 50 mm from tube plate and chisel out.
  • Remove remaining pieces by
  • chiseling and
  • knocking out by heating and cooling to achieve shrinkage.
  • Clean polish tube holes for dye check for any cracks, minor damage at the tube hole.
  • Diametrical clearance between tube and hole about 1.5 mm.
  • The ends of new tube cleaned thoroughly and carefully expanded by rolling into the hole and tube plate.
  • New tube protruded from tube plate by 6 mm at least.
  • Bell mouthing should be 1 mm for every 25 mm of tube outside diameter plus 1.5 mm.

(a)What are the causes of overheating and how can remedy to it.

(b) Explain boiler internal corrosion

(c) How to check and correction failure of furnace distortion and buckling.

(a) Overheating

Causes Remedy
High scale formation Proper boiler water treatment and dosage
High sludge formation Regular blow down
High oil and mud formation Regular cleaning of furnace and heat exchanger tube
Poor water circulation Maintain correct water circulation
Water shortage Maintain suitable boiler water level
Local overheating, incorrect raising team Good watch keeping
Faulty combustion, Direct flame impingement Maintain correct fuel-air ratio and proper burning

(b) Boiler internal corrosion

Internal corrosion of boiler is mainly caused by

(1) electro-chemical reaction

(2) direct chemical attack.

Corrosion

1. Hydrogen attack – Hydrogen ion generate by concentration of acid. Penetrate gain boundary of tube metal

2. Caustic cracking corrosion (caustic embattlement) – Due to high concentration of caustic soda of NaOH

3. Corrosion fatigue

  • Due to irregular water circulation through in high temperature reign, induce alternating stress set up, resulting series of fine crack

4.Gaseous corrosion –

  • O2(react with ferrous metal surface to form ion oxide result in pitting corrosion)
  • CO2 (react with water to form carbonic acid, reduce PH of water) Ammonia (attack copper base alloy in present of oxygen)

5.Corrosion by galvanic action –

  • Due to various parts of boiler structure at different potential. Result is wastage of metal at anode, hydrogen at cathodic surface.

6. Pitting corrosion – metal surface is contact with water having PH 6-10, containing dissolved oxygen.

(c) Furnace distortion, Causes

1. High scale, oil, mud and sludge formation

2. Poor water circulation

3. Water shortage

4. Local overheating, Incorrect raising of steam

5. Faulty combustion, Direct flame impingement

How to check

1. By sighting along the corrugations with a torch from inside the combustion chamber.

2. By taking a lath inside the boiler and lay it alone the corrugation at four points.

3. By furnace gauging.

Corrections

1.Heating pushing back into original shape. cracks test must be followed.

2. Defective portion cut out completely and a new piece (patch) welded into place.

3. If the deformation is acute, the only remedy is renewal.

4. No doubling plate for this kind of repair.

5. Temporary repair of weakened furnace by pressing back the deformation

(a) What is Thermal oil system, define the working temperature range of the system and where are they used?

(b) Sketch the thermal oil system with labeling major components.

(c) Compare the Thermal fluid system and steam system.

(a) Thermal oil system

  • Used to supply heat for various kinds of heat consumers like fuel oil tanks, separators and fuel heaters
  • Heat all types of cargo such as oil products and chemicals
  • Thermal oil as a heat transfer medium, compared to conventional plants using hot water or steam,

Advantage

  • temperature of 320˚C without any pressure.
  • temperatures up to 400 °C reached with synthetic oils

Thermal oil system comprised of Exhaust gas heater and independent heater

c) Conventional steam system and thermal oil system

Steam Boiler Thermal Oil
-Steam boiler systems operate at high temperature and pressure. -High pressure means costly, requires specialist engineers. -Most thermal oil systems are vented to atmosphere. -More safer than steam boiler.
-Efficiency losses due to condensation, flash loss, blowdown -About 30% more efficient then steam systems
-Corrosion problems. -Most synthetics oil used non-corrosive -Provide metal surface protection as light lubricating oils.
-Water is treated with chemicals, effect on environmental safety. -Closed loop systems, no blowdown required.
-Maintenance cost is high. -Initial Cost is low. -maintenance jobs and cost is low -Initial cost is high.

(a) What are the causes of boiler water contamination?

(b) State the defects normally found in the boiler parts due to boiler water contamination?

(c) Explain the test and action taken to prevent boiler water contamination.

(a) Boiler feed water is originally contaminated with main salt, other contamination to feed water are sea water and oil.

Oil contamination is caused by

  • Leakage in fuel oil heater, fuel tank heating coil. Over lubrication of steam machinery
  • Leaking oil return to observation tank, provided to trace of oil.
  • Seawater contamination is caused by
  • Condenser leakage, Feed water tank leakage. Evaporator carry over from F.W.G

(b) Defects normally found in the boiler due to boiler water contamination

1. Corrosion

2. Scale & sludge formation

3. foaming, riming & carry over

4. Chloride level high

5. Alkalinity level drop

(c) Test and prevention

 Oil contamination visually check in observation tank. Action taken for oil contamination

1. Filter at observation tank

2. Treatment by Epson salt

3. Rectify leakage & pressure test

4. Reduced boiler load and render surface blow down

5. Boiling off treatment with strong caustic solution

6. Shut down and boil out if heavy contamination

Prevention to be taken for oil contamination are:

1. Always check condensate drain and observation tank

2. Gradually heating up to fuel line and tank

3. Avoid water hammer and tube damage

4. Open condensate valve firstly and drain out condensate from steam line before use.

Sea water contamination in feed water tested by testing and chemical titration method. Action taken for S.W contamination

1. Blow down frequently

2. Reduce boiler load to minimum

3. Introduce extra anti foam chemical

4. Shut down & wash out if highly contaminated

Prevention to taken for sea water contamination are

1. Regular test to boiler water and feed water

2. Regular maintenance to condenser and pressure test

3. Fit zinc anode in condenser

4. Keep condenser S.W cooling pressure as low as possible