oral q with ans

8/9/2019 oral q with ans

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Compiled by Eswara Arun Kishore

[email protected]. What is ovality of auxiliary engine crank pin?

Combined effect of reduced effectiveness of L.O and directional thrust of the con rod.This is maximum at around 45 degree ATDCUneven loading of units and overloading

Max Allowed: 1/4th of the bearing clearanceRemoved By: Insitu Grinding and polishingReference: Fillet of crank webMax. Allowed Grinding: 2mm, because after grinding 2mm or more surface hardness reducesdrastically. Due to this maximum allowable grinding is 2mm.

Bottom bearing damage reason is the ovality, bearing clearance and condition of L.O supply

2. Why are concentric springs fitted for A/E cylinder head valves?

If the frequency of the natural vibration of air or exhaust valve springs is a harmonic of thecamshaft speed, then the spring may vibrate axially and are said to surge. Surge can beavoided by modifying the sizes of springs by arranging the springs in pairs and fitting oneinside the other.If one spring fails the valve is held up and is not damaged by striking the piston.The thickness of individual springs can be reduced as against original thickness.Normally two springs of different vibration characteristics are chosen.Moreover, the stiffness requirements and the space congestion at this place warrants aconcentric springs arrangement. The net stiffness is equal to the sum of individual stiffness.

3. What is SQUAT Phenomenon?

It is a venturi effect while vessel is moving on shallow water. A vacuum is created due towhich the draught of the vessel is increased there by increasing the engine load.Steering ability of the ship is reduced as a result.

4. What is a thermostatic expansion valve?

This is a regulator through which the refrigerant is metered from the high pressure side tothe low pressure side of the system. The pressure drop causes the evaporating temperature(saturation temp.) of the refrigerant to fall below that of the evaporator.

a. Avoids liquid refrigerant return to the compressor suction.b. Automatic expansion control and maintain 6 ~ 7 degree superheat.

5. What is the function of an L.P controller ?

The LP controller stops the compressor at low suction pressure caused by the closure of allcompartmental solenoids. When the pressure in the compressor suction rises due to solenoidopening, the LP controller restarts the compressor.

6. What is the function of an L.P cutout?

This is used to protect the compressor against the low suction pressure due to loss ofrefrigerant or blockage. If the a/c compressor suction pressure is allowed to fall belowatmospheric pressure then there exists a risk of moisture and air ingress into the system.


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[email protected]. What is a Coalescer?

A device consisting of a material whose surface provokes coalescence.The process of combining of larger droplets of a liquid like oil into larger droplets is calledcoalescing.

8. Why is there a starting air overlap provided in a diesel engine?

a. To give a positive starting in correct direction.b. Starting ability from any position.c. If any one of the valve is malfunctioning. Engine can still be started.

9. What is the significance of firing order?

a. Balancing of primary and secondary inertia forces.b. To assist the exhaust grouping.c. For distribution of stress over the length of crankshaft and optimum bearing loading.d. A firing interval for even turning moment.

10. What are the reasons for foaming in refrigeration compressor crankcase?

Due to rapid boiling out of the refrigerant dissolved in the oil when the pressure is suddenlyreduced.When the compressor starts operating, if a large quantity of refrigerant has been dissolved,larger quantity of refrigerant boils out and can be carried through the refrigeration lines.Reasons:

a. Liquid in the suction line (viz. TEV stuck open, incorrect super heat setting, sensingbulb not closing, overcharge etc.,)

b. Crankcase heater not working.c. Compressor capacity too high at the start.d. Expansion valve giving too small superheat

e. Oil charge is less.

11. Explain the functions of lube oil in refrigeration system

a. Lubricationb. Seal the clearance spaces between the discharge and suction sides of the compressor.c. Act as a coolant.d. Actuate capacity control.e. Dampen the noise generated by the compressor.

12. What are the various windlass safeties?

ELECTRIC:a. Electromagnetic brake.b. Motor overload protection.c. Short circuit protection.d. Restart delay timer.e. A Restart stop.

MANUAL:a. Manual brake / mech. Brake.b. Cable stopper.c. Slipping clutch (torque limiter).


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[email protected]. What are the constant tension winches?

It is a variation of the constant pressure and constant horsepower control for variablecapacity pumps. It is used to achieve constant tension winch system. In this case the pumpcontrol is automatically operative across the neutral such that constant system pressure andhence a constant motor torque is maintained whilst both drawing in and paying out.

20. What are the causes of turbocharger surging?

a. Rapid variation (reduction) in load.b. Chocked exhaust and air passage like scavenge ports, valve or air cooler etc.,c. Abnormal fuel system like a unit misfiring.d. Chocked air suction filter, fouling of the turbocharger, unbalanced output from the

engine, damaged exhaust valve, scavenge fire.

21. What are the causes of cylinder head cracking?

a. Scale depositsb. Inefficient cooling waterc. Uneven tightening of bolts and fuel valvesd. Fluctuating cooling water temperature (excessive temperature gradient)e. Overloading or racing of enginef. Faulty relief valveg. Mechanical failure due to gas corrosion, acidic corrosion due to leaky exhaust valvesh. Water side corrosion

22. What is the normal relief valve setting of cylinder head in a diesel engine?

10 ~ 14.5% more than the working pressure about 120 bar (some what higher thanmaximum pressure)

23. State the advantages of uniflow scavenging a. Simple liner constructionb. Long skirt (for piston) not requiredc. Stroke length can be increasedd. High scavenging efficiencye. High thermal efficiencyf. Low grade of fuel can be burntg. Uniform wear of piston rings and linerh. Less thermal stressesi. Less intermixing of scavenging air with the exhaust gas

j. Exhaust valve can be made to open late – more work, close early – scavenge air ismore utilized.

24. Why cylinder liner wear is more at the top?

a. High temperature exposure due to the combustion gasesb. Loss of liner lubrication in low speed dieselsc. Corrosion, predominantly acidic due to combustion productsd. Fuel impingement, depositse. Change of direction of the piston, which causes to a step like formation at the reversal

point


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25. What actions do you take incase of stern tube of the ship starts leaking?

a. Maintain low head.b. Use higher viscous oil.c. Replenish periodically to counter for the oil loss.

d. Drain off the water periodically.e. Try to remove foreign particles by changing direction of shaft.

26. How do you test a fresh water generator plant for leaks?

a. Close the outlet of the distillate pump, vacuum breaker valve, bottom blow off valveand feed water valve

b. Inject air into the evaporator shellc. Keep the shell pressed up to about 1.0bar gauged. Sprinkle soap solution on to the jointings, packings, and suspected areas of the shell

27. What are the reasons for a piston crown to crack?

a. Casting defectb. Thermal stresses due to cold starting air and scavenging airc. Scavenge fired. Overheated piston(cooling failure, cooling side deposits due to oxidation of the cooling

oil)e. After burningf. Faulty fuel injection system (more penetration or loss of atomization)

28. What are the reasons for black smoke from a diesel engine?

a. Poor combustion due to faulty injection systemb. Low compression

c. Insufficient scavenging aird. Fouled exhaust systeme. Broken piston ringsf. Ineffective lube oil sealg. After burning, bad fuel and other fuel assisted faultsh. Faulty cylinder lubricationi. During starting, it is inevitable as the engine maker sets the starting fuel index to a

fixed value. At this index there is insufficient air, low piston speed, cold combustionchamber, low fuel injection pressure etc., each compounding the cause for blacksmoke

29. What are the critical speed effects?

Resonance, torsional vibration, fatigue failure of componentsCan be remedied by:

a. Detunersb. Vibration dampersc. Electric vibration compensator unit


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[email protected]. What are the types of vibration in a diesel engine and which is the mostdamaging?

Types of vibration:a. Linear vibrationb. Torsional vibration

c. Resonant vibrations involving any two of the above or may be combinational

Most damaging form of vibration is the torsional vibration mode, affecting crankshaft andpropeller shafting.

31. What is a node?

A node is found where the deflection is zero and the amplitude changes its sign in a vibratingmedium. The more the nodes in a given length the higher the corresponding naturalfrequency.

32. What is a forcing frequency?

W.r.t the crank shafts, the forcing frequencies are caused by the firing impulses in thecylinders.Firing impulses superimpose on one another and appear as a complex waveform representedby harmonics –

1x cycle frequency: first order harmonics of firing2x cycle frequency: second order harmonics3x cycle frequency: third order harmonics and so on…

33. How can the frequency of resonance, the forcing impulses and the resultantstresses adjusted?

a. By adjusting shaft sizes

b. Number of propeller bladesc. Firing orderd. Using viscous or other damperse. Using balancing weightsf. Detuning coupling

34. What is balancing?

Balancing is a way of controlling vibrations by arranging that the overall summation of theout of balance forces and couples cancels out, or is reduced to a more acceptable amount.

35. Explain the vi bration characteristics of low speed 2-S engines

a. External unbalanced momentsb. Guide force momentsc. Axial vibrations in the shafting systemd. Torsional vibrations in the shafting system

36. What is 1st order moment?

These moments acts in both vertical and horizontal directions. For engines with 5 cylindersor more, the 1st order moments are of rare significance to the ship but it could be of a


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[email protected] magnitude in the 4 cylinder engines. Resonance with a 1st order moment mayoccur for hull vibrations with two and/or three nodes. 1st order compensator can beintroduced in the chain tightener wheel. It comprises of two counter rotating massesrotating at the same speed as the crankshaft.

37. What is a second order moment?

The second order moment acts only in the vertical direction and precaution needs only beconsidered for 4, 5 and 6 cylinder engines. Resonance with the 2nd order moment may onlyoccur at hull vibrations with more than 3 nodes. A 2nd order moment compensatorcomprises two counter rotating masses running at twice the engine speed.

38. What are the methods to cope up with the second order moments?

a. A compensator mounted on the aft end of the engine driven by the main engine chaindrive mechanism.

b. A compensator mounted on the fore end driven from the crankshaft thus a separatechain drive.

c. A compensator on both aft and fore end completely eliminating the external 2nd ordermoment.

39. What is an electric compensator?

It is electrically driven compensator preferably located in the steering gear compartment,where deflections are the maximum and the effect of the compensator is maximum. Such acompensator is synchronized to the correct phase relative to the external force or momentand can neutralize the excitation. The compensator requires an extra seating to be fitted.

40. What are guide force moments and their types?

The origin of the guide force moment is the angularity of the connecting rod. It is the

vibration of the engine about the foundation bolts.Guide force moments are caused by the transverse reaction forces acting on the cross headdue to the con rod crankshaft mechanism.Guide force moments may excite engine vibrations moving the engine top arthwartshipscausing a rocking (excited by the H moment) or twisting (excited by X moment) movementof the engine.Guide force moments are harmless except when the resonance occurs in the engine doublebottom system. As a precaution, top bracing is installed between the engine’s upper platformbrackets and the casing side for all its 2S models.

41. What are different types of the top bracing for a diesel engine?

a. It comprises of the stiff connections (links) either with friction plates which allowsadjustment to the loading conditions of the ship

b. A hydraulic top bracing – by using the top bracing natural frequency will increase to alevel where resonance will occur above the normal engine speed.


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[email protected]. How are the axial vibrations caused in the crankshaft? How are theyremedied?

When the crank throw is loaded by the gas pressure through the conrod mechanism, thearms of the crank throw deflect in the axial direction of the crankshaft, exciting axialvibrations. These vibrations may be transferred to the ship’s hull through the thrust bearing.

Its remedy is to axially dampen the crankshaft vibrations.

43. How is torsional vibrations generated?

The varying gas pressure in the cylinders during the working cycle and the crankshaft /conrod mechanism create a varying torque in the crankshaft. It is these variations that causethe excitation of torsional vibration of the shafting system.The torsional excitation also comes from the propeller through its interaction with the non-uniform wake field.Remedy: modify crankshaft natural frequency by adjusting the diameter. Use a torsionaldamper.

44. What is under critical running?

The natural frequency of the one node vibration is so adjusted that the resonance with themain critical order occurs about 35~45% above the engine speed at specified maximumcontinuous rating (MCR). The characteristics of an under critical system:

a. Relatively short shafting systemb. Probably no turning wheelc. Turning wheel with low inertiad. Large diameter of the shaftinge. Without barred speed range

45. What is overcritical running?

The natural frequency of the one node vibration is so adjusted that the resonance with themain critical order occurs about 30~70% below the engine speed at the specified MCR. Thecharacteristics of the system are:

a. Turning wheel may be necessary on the crankshaftb. Turning wheel with a relatively high inertiac. Shaft with relatively small diameter (shaft material has to be of high UTS)d. With a barred speed range of about +/- 10% w.r.t the critical engine speed

46. If resonance occurs, what is the solution?

The following modification(s) have to be carried:a. Lanchester balancers, either on the engine or electrically driven units usually located

in the steering flat, compensated for ships vibration caused by the 2nd order verticalmoment

b. Counter balancing weights on the crankshaft to be adjusted for compensating the firstorder vibrations

c. Combined primary and secondary balancersd. Adjusting the side stays

47. How to prepare a DB fuel oil tank for a survey/inspection?

a. Empty the oil, strip with portable pumps if required


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[email protected]. Clean the tank with sea water and pump it through the oily water separatorc. Ventilate the tank(s) with a blower specially provided for the purpose, always cross

ventilate i.e. there should be at least two openings, each for entry and exit for the aird. Check the space for explosive gases at various points suitably, more sampling should

be carried out at the corners at the bottom most part of the tanke. Obtain the necessary certificates and get the checklist completed

48. Why are the CO 2 bottles provided with dip tubes?

It is to ensure that only liquid is drawn during release. The liquid expands after the nozzlesand assumes the gaseous state. This will prevent co2 freezing and blocking the nozzleAlso it achieves the 85% discharge in 2 Minutes as liquid part represents a large volume ofgasThe materials used in its construction are copper, stainless steel

49. Why a crankcase relief door is not fitted in the refrigeration compressorcrankcase?

a. Possibility of the contamination of the refrigeration system by air by leaksb. Oxygen is not available in the compressor crankcasec. The incoming refrigerant temperature is low and chances of hot spots is lowd. Crankcase forms the suction chamber of the compressor and chances exist that the

compressor may draw in air and moisture

50. Why heaters are provided in the crankcase of a refrigeration compressor?

a. To avoid carry over of the lube oil because at low temperature, the separation of therefrigerant and the oil is difficult

b. To condition the lube oil, by maintaining the viscosity so that the lubrication iseffectively carried out.

c. This prevents the lube oil achieving its floc point which may cause narrowing or

chocking of the passages (flocculation)

51. What are the causes of a centrifugal pump reduced output?

a. Friction and leakage losses, loss of suction head, chocked suction filter, worn out wearring, air ingress in the suction side

b. Low voltage is applied to the pump motorc. Cavitations on the impellerd. Bad maintenance, incorrect fixing up of the parts after overhaul

52. What are the causes of vibration in the vertical centrifugal pump?

Misalignment of the shaft, worn out bearing, foundation bolts loose, hydraulic clearances -not proper on the impeller, coupling bolts / seating damaged, bottom bush worn out, heavyobjects/debris deposits, and corrosion/erosion on the rotating parts

53. What is volumetric efficiency of air compressors?

Actual volume of air drawn in / swept volume


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[email protected]. What is compression ratio?

(Swept volume + clearance volume)/clearance volume

55. What is brake thermal efficiency?

Ratio of the energy developed at the brake to the energy supplied. Amount of heat liberatedduring the combustion to the heat equivalent at the brake

56. What is the function of a Solenoid valve in the refrigeration system?

There is an electric signal actuated valve in the liquid line of the refrigeration system justbefore the thermostatic expansion valve. This is being actuated by the thermostat in therefer compartment. The solenoid shuts off the refrigerant supply if the compartment issufficiently cooled to the lower set point of the thermostat. Also it connects the supply whenthe temperature of the compartment goes high i.e. above the thermostat higher set point

57. What is the function of the back pressure valve in the refrigeration system?

Back pressure valve is fitted just at the exit of the refrigerant from the evaporator coil in amulti temperature rooms system. This being fitted at the exit of the compartments whosetemperature is set higher (usually at about 4~5 degrees centigrade). The function of thevalve is to maintain equilibrium of the system as the pressure of the gas at the exit of eachcompartment differs. More over the back pressure valve creates a back pressure on theevaporator coil and ensures that most of the liquid refrigerant is made available to the lessertemperature requirement compartments as their demand for the refrigerant is higher thanthe compartments being maintained at a higher temperature. It is spring loaded non returnvalve

58. What is the function of a H.P cut out in a refrigeration system?

This is a safety device (trip) provided in the discharge of the compressor. It functions to tripthe compressor if the pressure in the HP side goes high above the working level

59. What is the function of the driers in the refrigeration system?

The filter/drier is installed in the main liquid line of the system to absorb any moisturepresent in the refrigerant. It consists of activated alumina or silica gel in a renewablecartridge. It also accommodates the charging connection

60. What are the usual stern tube bearing clearances?

a. Water cooled stern bearing clearance: 8.0mm (8~12mm)b. Oil cooled stern tube bearing: 1.87~2.0mm

61. What is a usual volumetric efficiency of a diesel engine?

a. Naturally aspirated engine: 0.85~0.95b. Supercharged engine: up to 4.0c. For 2S engine: 0.85~2.5


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[email protected]. What is a usual propeller drop usual value?

1mm/160mm of the shaft diameter

63. What are the advantages of a thin shell bearing?

a. Increased fatigue resistant propertiesb. High load carrying capacitiesc. Embed abilityd. Conformabilitye. Bedding not requiredf. Easy storage, easy fitting, light in weightg. Increased (enhanced) mechanical propertiesh. Better heat transfer due to reduced thickness and uniformity of the contact with the

bearing housing

64. What are the typical bearing failures?

a. Fatigue failure (cracks)b. Tin oxide encrustation (black SnO 2 )c. Wiping damage of the bearing surfaced. Tearing of the overlaye. Acidic corrosionf. Cavitations, erosiong. Dross inclusionh. Spark erosioni. Bacterial attack damage (honey colored deposits on the bearing surface)

65. What are the advantages and disadvantages of the synthetic lube oils?

Advantages:

a. Better low temperature fluidity and pump ability, due to nil wax contentb. Better oil retention at high temperaturesc. Lower friction lossesd. Reduced thickening of the oil in service due to oxidatione. Lower deposits at higher temperature due to resistance to oxidation properties and

thermal stabilityDisadvantages:

a. Increased cost of the lube oil (about 6~12 times)b. Poor availability

Uses:a. Air compressorsb. Purifiersc. Hydraulic units

66. What is the purpose of the lube oil analysis?

a. To determine any deterioration in lube oil properties or additives levels and assess itssuitability for further service

b. To determine the type and level of the contaminants held within the oil which indicatethe rate of contamination and effectiveness of the purification process

c. To predict the internal wear rate on the machinery componentsd. To lengthen the time between overhauls or surveys


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67. When is the lube oil said have deteriorated?

a. TBN reducesb. Viscosity reducesc. Flash point reduces

d. Oxidation increasese. Water content highf. Insolubles increaseg. Dispersancy increases

68. What are the problems in cast iron welding?

a. Brittleness (cracks easily)b. High carbon content in the form of graphitec. Close grain structured. Poor thermal conductivity and differential coolinge. Possibility of stresses and distortion

69. How is a propeller drop measured?

a. Turn the engine to coincide with the mark on the liner and the stern tube or normalreference is taken to be that the engine’s unit 1 will be in TDC prior measuring thepropeller dropThis could be also arranged as with a designated blade of the propeller up wards whilemeasuring this drop. Blades are assigned alphabets A, B, C, D and so on.

b. Take the poker gauge reading and the compare with the previous readingc. Bearing clearance : 2mm (oil sealed)

: 8mm (sea water lubricated)Bearing length is about 2xdia of the shaft for oil cooled stern tube bearing4xdia of the shaft for sea water lubricated stern tube bearing

70. Compare an engine flywheel and its governor

a. A governor maintains the speed of the engineb. A flywheel controls the cyclic fluctuations of the engine RPMc. Flywheel works on the virtue of the inertia alone and the governor uses the inertia

principle to actuate the fuel linkages to counter the changes in the engine RPM

71. Why are tie rods provided?

Tie rods are provided to keep the whole engine structure in compression which:a. Increases the fatigue strength of the engine structure as it is the tensile stress which

causes fatigueb. Maintain running gear alignment to avoid fretting

The firing forces that press down the bearing saddle also attempt to push up the cylindercovers, the net effect being to put the whole engine structure into tensile loading. So the tierods are tightened such that the engine structure is maintained in compression even duringthe peak firing conditions and that the engine is not subjected to the tensile loading.


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[email protected]. Why tie rods are placed close to the centerline of the crankshaft?

During firing, the transverse girders are subjected to a bending moment as the saddle ispushed down by the crankshaft acting on the cylinder head. To limit this bending effect andconsequent distortion of the bearing housing the tie rods are positioned as close as possibleto the centerline of the crankshaft.

73. Where is a thrust bearing installed in an auxiliary engine? And why?

Axial location of the crankshaft may be required if the coupling does not incorporate a thrusthousing. This is achieved by forming white metal rings on the sides of one main bearing shellthat allows the shaft to run with a small clearance between running faces on the twoadjacent webs.In some engines a small collar may be provided at one side of the bearing. It is important toappreciate that only one such locating bearing should be fitted to any one shaft, otherwisethe differential thermal expansions of frame and the crankshaft may cause problems.

74. What are the environmental problems with the use of CFCs?

a. CFC released into the atmosphere are broken down by pyrolysis to release chlorineatoms which catalytically destroy ozone layer.(this layer in the stratosphere acts as afilter to the UV radiation from the sun)

b. Furthermore CFCs along with other greenhouse gases inhibit radiation from theearth’s surface thereby contributing to the global warming.

75. What is a pH value?

It is the logarithm of the reciprocal of the hydrogen ion concentration expressed in gram ionper liter.Pure water at 25 degree centigrade consists of equal concentration of the hydrogen and thehydroxyl ions and equal to 10 -14 gram ion per liter. If the hydroxyl ion concentration exceeds

the hydrogen ion concentration then the solution is basic and vice versa is acidic in nature.pH value = log [1/H+]If the water temperature is increased, the concentration of the hydrogen ion increases andhence acidity.

76. Why is a man hole door elliptical in shape?

Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical holeis lesser in size than the corresponding circular hole. More over it is prime concern to have asmoothed generous radius at the corners to eliminate stress concentration. Hence othergeometrical shapes like rectangle and square are ruled out.To compensate for the loss of material in the shell due to opening, a doubler ring has to beprovided around the opening. The thickness of the ring depends on the axis length along thedirection in which the stresses are maximum and the thickness of the shell. It is important toalign the minor axis along the length of the vessel, as the stress in this direction ismaximum.

Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t=thickness of the shell platingCircumferential stress: Pd/4tMore over a considerable material and weight saving is achieved as minor is along thedirection of maximum stress.


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77. Why is the fridge compressor belt driven?

a. A slight misalignment is a problem or vibration of the electric motor may lead to shaftseal leakage, leading to loss of the refrigerant. So minimize these the fridgecompressor is belt driven.

b. In case of the liquid entry into the refrigeration compressor, the belt drive gives alimitation of the damage owing to the slip in the belt and flexibility of the beltmaterial.

78. Why intercooling is provided in an air compressor? And why is thecompression distributed into stages?

a. By employing the interstage cooling we are trying to achieve an isothermalcompression cycle. So least work is expended in the process.

b. The air outlet temperature after compression is lowered by intercooling. So oxidationof the lube oil is prevented. Also good lubrication is achieved.

c. Lesser deposits in the air system.d. Intercooling increases the air density and hence reduced volume of the HP

compression chambers is possible.e. It facilitates removal of moisture by condensation at the intercoolers.f. To facilitate intercooling the compression is distributed into stages. Also even load

distribution is achieved over the cycle.

79. What if the compressor motor connections are reversed after overhauling?

a. The lube oil pressure will not be sufficient for lubrication so the compressor may tripon low lube oil pressure. The moving parts may get damaged due to the failure of thelubrication.

b. The cooling water pump which is also shafted driven usually does not build up enoughflow/pressure hence the compressor may trip of the cool water non flow or high air

temperature.

80. If viscotherm is absent or damaged how do you maintain the fuel oilviscosity?

The required viscosity prior injection and the viscosity of the fuel oil at 50°C are provided bythe fuel oil analysis report. Basing on the viscosity nomogram the required fuel oil heating isdetermined. The steam inlet to the fuel oil heater is manually adjusted to maintain thetemperature and a close observation has to be maintained on the steam pressure andtemperature of the fuel oil at the outlet of the heater.

81. What are the reasons for the error between the helm order and the angleshown locally on the steering gear unit?

a. Air in the hydraulic telemotor systemb. Buffer spring too weak or stiff, faulty hunting gearc. Instrument error/defectived. Worn out linkages


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[email protected]. Why are the accumulators used in the hydraulic systems?

a. To absorb shock due to load variation or sudden change in the direction of flow,impact loading

b. To maintain the circuit pressure by compensating for the loss due to leaks or pressureincrease due to rising temperature

c. To supplement the pump delivery where multiple circuit operations have wide flowvariations with a short term peak demand in excess of the pump capacity.Accumulator charge can take place during low demand periods to meet maximumdemand later

83. Explain the cross head slipper lubrication

a. The lubricating oil is fed to the guide shoes by a pipe from the main lube oil systemb. The lubricating oil may also be fed from the drilled passages in the pin to the slipper

faces

84. What is the material of the CO 2 bottle and its accessories?

CO2 bottle: solid drawn seamless manganese steelCable: phosphor bronzeSeal/bursting disc: thickness 0.3mm, phosphor bronzePipeline: solid drawn MS galvanizedSiphon tube: copper tubeCutter: 120° /travel 19mm

85. How will you decide for reentry into the engine room after flooding it withCO 2

Re-entry is determined bya. Heat build up due to the scale of the fire and the elapsed time after release

b. Has the fire been extinguished or chances of a smoldering fire existsc. Ship’s position, condition and the prevailing weather (ship may be listing to the angleof progressive flooding etc.,)

d. The location of the entry pointe. Risk analysis outcome

86. What is the quality of the vapor coming back to the compressor suction inthe refer system? In addition, how will you ensure that the vapor has adequatedegree of superheat?

a. The condition of the vapor coming to the compressor suction line should haveadequate degree of superheat

b. The condition is checked by reading the pressure of the returning vapor and itscorresponding temperature from the P-T chart provided for the specific refrigerant.This temperature is compared with that of the evaporator outlet and the degree ofsuper heat is expressed as the difference in the temperature.

87. What is the length of the crank web?

Length of the crank web = stroke length/2


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[email protected]. What is lignum vita?

In the traditional sea water lubricated stern tubes the bearing material consisted of thestaves of the wood called lignum vitae. This has a property of lubrication in the presence ofsea water. They are fitted with the grains in the axial direction for economy and are shapedwith V or U grooves between them at the surface to allow for access to water. They also act

as a debris collector points. The staves are held in place in the bronze boss by bronze keysattached to the bush by counter sunk screws. Bearing length is equal to 4times the shaftdiameter.

89. What are the safeties in the fridge system?

a. HP cut outb. Differential lube oil pressure cutoutc. LP cutoutd. Relief valve in the condensere. Belt drivenf. Cylinder head relief valveg. Cooling water low flow/high temperature alarmh. Motor overloadi. Oil separator

j. Drierk. Mech. Seall. Unloaders /capacity controllersm. Non return shut off valvesn. Sensors – temperature, pressure

90. How will you know the presence of air in the refrigeration system? Explainthe procedure for purging air

a. High condenser pressure

b. Small bubbles in the sight glassc. Compressor discharge pressure high/running hotd. More superheate. Pressure fluctuationsf. Inefficient working

PROCEDURE FOR PURGING AIRa. In the normal operation of the system, measure the liquid refrigerant pressure,

temperature at the outlet of the condenser/reservoirb. Check the corresponding saturation temperature for the recorded pressure of the

liquid refrigerant from the P-T chart for the same refrigerantc. Compare the measured temperature with the determined saturation temperature for

any sub-cooling and adjust the flow of the cooling water through the condenser toachieve near saturation condition inside the condenser,

Then,d. With the condenser liquid refrigerant outlet valve closed, circulate cooling water, start

the compressor and pump down the liquid to the condenser/reservoir, checking thepressure in the suction line. If this pressure is allowed to drop down below theatmospheric pressure then there could be chances of air ingress into the system

e. Circulate the cooling water till the cooling water outlet and the inlet temperaturesequal, a check to ensure complete pump down operation

f. Check the condenser sea water out let temperature, check the refrigerant pressurecorresponding to its temperature from the P-T chart of same refrigerant


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[email protected]. Due to the presence of air they don’t agreeh. Release air from the condenser, through the vent cock until the pressure of the

refrigerant in the condenser corresponds to the saturation pressure at the sea wateroutlet temperature

91. What is the material of the boiler gauge glass?

The material used in the gauge glass is a special toughened glass containinga. Silicon oxide or magnesium oxideb. Borosilicate or lime soda glass

92. What is the material of a boiler tube?

Low carbon alloy steels containing chromium, nickel, molybdenum

93. What is the material of the ship side valve?

BODY: Nickel-Aluminium bronze / cast steelStem/Seat/Disc: Monel metal (cupro nickels of varying proportions are used popular being aCu:Ni = 2:1)The cupronickels are known for their great resistance to the sea water corrosion, erosion bythe particles in the sea water, and strength.

94. What is the material of the propeller material?

a. Nickel aluminium bronze (nickalium)Copper: 55~62%, Aluminium: 0.5~2.2%, Nickel: 0.5%, Manganese:0.5~1.0%, Iron: 0.4~1.5%, balance is Zinc

b. Manganese bronzeCopper: 58%, Iron: 1%, Aluminium: 1%, Manganese: 1%, Nickel: 0.5%, Zinc:38%, Tin: 0.5%

95. What is the general composition of the stainless steels?

Chromium: 18%, Nickel: 8%, Carbon: 0.12%

96. What is the material of the 4S engine conrod?

a. Forged steel: Open hearth plain carbon steelUTS: 432~494 MN/m2% Elongation: 25~30%Fatigue limit: 208 MN/m2 (push pull)

b. Nickel steel, 3%NiUTS: 695 MN/m2%Elongation: 20%Fatigue limit: 309 MN/m2 (push pull)

METHODS OF TIGHTENING:a. Measuring the extension of the boltsb. Use of the calibrated torque wrenchesc. Hydraulic tensioningd. Angle tightening


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[email protected]. What is the material of the foundation bolts?

High tensile steel

98. What is the material of the tie rod?

High tensile steel

99. What is the material of the double bottom plug?

Silicon steels

100. What is the material of the crankshaft?

Forged low carbon alloy steel. Carbon: 0.12% and less

101. What are the materials used for the diesel engine’s liner and piston rings?State their principle differences

Generally the materials used for the piston rings are harder than the liner material. This isdue to the fact that the rings are subjected to wear always during their operation but onlythe portion of the liner in contact with the rings wears.Material used for the liner is generally the nodular cast iron, which is tailored to haveexpansion along the length and negligible expansion circumferentially. Alloying materials areadded to improve certain characteristics like vanadium and titanium.Piston rings are cast and machined from graphite grey cast iron. This ring may includechromium, nickel & copper as alloying substances.The prime property which distinguishes it from the liner material is that it has to flexcircumferentially.This is of primary concern for running in and to match the contour of the wearing linersurface. Also they have to form an effective sealing of the combustion gases.

102. What are the liner wear rates? And how is it achieved?

Old engines: 0.1mm/1000hrsModern engines(2S): 0.03mm/1000hrsModern engines(4S): 0.12mm/1000hrs

This is achieved by:a. Highly alkaline lube oilb. Load dependant jacket cooling water temperature controlc. Good quality of cast iron with a hard faced. Careful design of the piston ring profilee. Improvement in lube oilf. Multilevel cylinder lubricationg. Condensate separation from the scavenging airh. By use of the anti-polishing ring or the piston cleaning

103. Explain why stainless steel is resistant to corrosion?

Stainless steel depends on the formation of a protective oxide film, tenacious chromiumoxide for resisting corrosion. This film is formed spontaneously on exposure to air or wellaerated water.


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[email protected] this oxide film, their corrosion resistance is only slightly better than otherengineering steels.

104. What is the material of the fuel valve needle and body?

Needle: high speed steel

Body: case hardened steel

105. What is the material of the chain and its tightener arrangement?

High tensile steels

106. Quote some important clearances in the rudder system

Jumping clearance: 6mmClearance at raphson slide mechanism: 16~19mmPropeller drop: 1mm/160mm diameter of the tail shaftPintle clearance: 1.1mm~3.3mm

107. What are the usual pressures to which the boilers are tested?

New boilers, if > 6.9bar working pressure, 1.5xdesign pressureIf < 6.9bar working pressure, 2.0xdesign pressureAfter major repair, 1.25~1.5x working pressure, duration of the testing: 30Min.

108. Explain the purpose of the hunting gear

a. To put the pump on stroke graduallyb. To stop the pump at the end of the stroke graduallyc. To lock the rudder at desired position till further movement is given at helmd. To transmit movement of telemotor to pump

e. Spring in the hunting gear store extra control movement to ensure that the pumpoperates at the maximum capacity for major part of the turning operation

109. Differentiate between the terms priming and foaming with reference to theiroccurrence in a steam boiler

Both refer to the carry over of water into the steam outlet. Priming is due to themechanical/physical aspects and the foaming refers to certain insouble/solubles in the boilerwater, which by the principle of increased surface tension cause priming.The various reasons for priming:

a. High water level in the boilerb. Rapid changes in the steam demandc. Safety valve lifting frequently due to its malfunctiond. Rough weather causing heavy rolling/pitchinge. Rapidly raising steamf. High salinity of the boiler water

Foaming is the formation of unbroken chain of bubbles on the surface of boiler water. Acommon cause of the same is the oil contamination.

110. Mention some important mechanical properties of metals

a. Elasticity:


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[email protected]. Hardness: Resistance to abrasionc. Plasticity:d. Toughness: Ability to absorb maximum energy before fracturee. Ductility: Ability of the metals to deform plastically under tensile forcef. Stiffness: Ability to withstand deformationg. Malleability: Ability of the materials to deform plastically under compressive force as

in forging or rollingh. Resilience: Resist shock and impacti. Brittleness: Tendency of the material towards brittle fracture. Brittle fracture is the

failure of the material without plastic deformation j. Creep: Plastic flow under constant load application or heatk. Weld ability:l. Endurance: Ability to withstand alternating stressesm. Cast ability:n. Strength: Ability to withstand rupture

111 . What is a tie rod bolt pinch screw? And what is its purpose?

Pinch screw is normally provided at the foot of the engine cylinder jacket to stop the tie rodfrom vibrating during the normal service of the engine.The pinch screw is fitted at the antinodal point of the tie rod to limit its transverse vibrationamplitude, thereby preventing its fracture due to vibrations. These can be arranged as agroup of three screws positioned equilaterally at the antinodal point. Each screw consists of astud, which is hand tightened by screwing the outer sleeve and held in place by a lock nutwhich is tightened to a torque specified by the manufacturer.

112. What is the course of action after finding that a bottom end bolt isslackened?

a. Check the length of the boltb. Check whether it is within the limits

c. Check for cracks / surface finish. Check the threadsd. The tie rod can be rolled over a flat surface coated with Prussian blue. Any twists in

the rod are revealed by the Prussian blue lines on the tie rod which get adhered alongthe twisted plane

e. If found alright, tighten the bolt and check the remaining bolts

113. Define higher calorific value and the lower calorific value

[H2O formed by the hydrogen in the fuel oil cannot exist as water at the high temperaturesin an internal combustion engines. The water formed by the combination of hydrogen andoxygen absorb the heat from the combustion and forms steam. Therefore, some amount ofavailable energy is lost in converting water into steam. This energy is not available to theengine.Therefore, the calorific value of the fuel reduced by this amount presents the actual calorificvalue available to the engine.] - This definition is given by reeds and I feel this hasto be altered after looking into the MANBW manual, which provides a graph tocalculate the Lower calorific value based on the Specific Gravity and Sulfur content.

Therefore, the amount of heat loss due to the inclusion of sulfur, which cannot be separatedby normal fuel oil treatment and its subsequent oxidation to SO x warrants the entire calorificvalue to include correction for corresponding fuel content in a specific mass of fuel sample


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[email protected] the energy loss due to sulfur oxidation. Corrections should also include for ash & watercontent.Therefore, to get the practical scenario two specific calorific values are mentioned Lowercalorific value and the higher calorific value.Lower calorific value = higher calorific value – the energy loss in converting the mass of the[ water into steam ] + sulfur to sulfur oxides + Loss of specific enthalpy due to ash content

present in unit mass of fuel.

114. Explain gear pumps w.r.t the materials used and the clearances

Rotors and shafts are integrally forged of Nitraalloy steel.Gears are case hardened, medium carbon steel. They are hardened all over and groundfinished after hardeningCasing and bearing housing are close grained grey cast ironShafts are supported by white metal bearing or roller bearings or bronze bushes on the freeendsLiquid being pumped is forced out after being carried around the gear teeth between thegear teeth and the casing.Backflow is limited by:

a. Minimizing the radial clearances between the teeth of the gears and the housingb. Increasing the number of teethc. Optimizing the side tolerances /play

Gear pump suitable for operating up to 25bar and can achieve displacement volume of0.35~1.0 liters/revolutionClearances between the gear teeth and the housing are of the order 0.02~0.03mm

115. What are the advantages and disadvantages of resin chocks?

ADVANTAGES:a. 100% contact on uneven surfaces

b. Cheaper to install as no hand fitting is requiredc. Don’t corrode and are resistant to most of the chemicalsd. As they achieve good contact, there is little chance of fretting, thus cheaper, shorter,

non resilient bolts can be used. These permit a reduction in the bolt tension by afactor of 4

e. Avoid vibrationsDISADVANTAGES:

a. Overstressing of the bolts causes the resin to shatter and breakb. Maximum temperature is limited to about 80°C

116. Explain the cavitation in the bearings

Vaporization due to oil pressure falling locally below vapor pressure causes bubbles in the oil,which when goes to higher pressure region, collapses and shock wave is generated causingheavy impingement. The causes:

a. High oil temperatureb. Low oil pressurec. Vibrationd. Oil contamination


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[email protected]. What are the Nimonic and Stellite coatings?

These are considered to be the hardened materials by the process of metallic cementationNimonic: carbon, chromium, Titanium, Aluminium, Cobalt, Molybdenum, Iron, NickelThere could be other constituents such as Manganese, copper, silicon

Stellite: They are alloys of Cobalt, and Chromium, with the addition of varying amounts oftungsten and other elementsThey are very resistant to corrosion and abrasion. Retain their hardness at a red heatSince they cannot be forged, they must be cast direct to shape or deposited by welding

118. Why is an equalizing line provided in the refrigeration system?

It is used in the installations where a large drop in pressure occurs in the evaporator. In theexpansion valve, the pressure acting outside (top) of the bellow corresponds to thesaturation pressure plus the degree of superheat of the refrigerant leaving the evaporator.This pressure is trying to open the valve against the spring force from below the diaphragm.The external equalizer connection has a saturation pressure of the refrigerant leavingevaporator, to act below the diaphragm. Therefore the saturation pressure from the externalequalizer connection balances the saturation pressure of the sensing bulb leaving only thepressure due to degree of super heat only to oppose the spring force. Therefore, this degreeof superheat is supposed to open the expansion valve.By this method, we are getting a control over only the degree of superheat of the refrigerantleaving the evaporator coil. This is important to ensure proper utilization of the refrigerantand that no liquid refrigerant reaches the suction of the compressor.

119. What are the reasons for short cycling of a refrigerant compressor?

a. Refrigerant charge is too lowb. Frosting or clogging of the evaporatorc. Dirty suction strainer

d. Low pressure control differential too smalle. Wrongly adjusted capacity regulatorf. Refrigerant vapor in the liquid lineg. Too much cooling waterh. TEV faultyi. Too high compressor capacity

120. What is viscosity? Differentiate between the kinematic viscosity and thedynamic viscosity

Defined as the resistance of fluids to change of shape, being due to the internal molecularfriction of molecule with molecule of the fluid producing the frictional drag effect.Absolute (Dynamic) viscosity is numerically equal to the force to shear a plane of fluidsurface of area of a unit square meter, over another plane surface at the rate of one meterper sec, when the distance between the surfaces is one meter.Kinematic viscosity is the ratio of the absolute viscosity to the density at the temperature ofviscosity measurement.Viscosity index is a numerical value which measures the ability of the oil to resist the changein viscosity with the change in temperature. A high viscosity index shows a good resistanceto the change in viscosity with change in temperature.


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[email protected]. What is an Otto cycle or the constant volume cycle?

This is the constant volume cycle. Although no actual engine cycle operates strictly followingthis ideal cycle, the analysis of this cycle provides a tool for comparison of performances ofactual engines under different operating conditions.The most important noted difference between this ideal cycle and the normal cycle is that

this is a non-flow cycle involving an ideal gas whereas the actual cycle is a flow process andthe gases are real.This cycle is explained as follows:At the beginning of the process the cylinder is assumed to be full with a charge of fresh air.The air is compressed isentropically following the law PV

γ = constant. Heat is then added to

the same mass of air at constant volume. This point represents the maximum pressure andtemperature in the cycle. From here the air is expanded isentropically to the initial volumeand then the heat is rejected at the constant volume.

122. What is a Diesel cycle?

This thermodynamic cycle is first analyzed by Rudolph Diesel. This is a slight variation of theabove constant volume cycle, the difference being that the heat addition in the cycle takesplace at constant pressure. The other processes during compression, expansion, and heatrejection remain same as with the constant volume cycle.

123. What actions do you take incase of an EGB Soot fire?

The oxygen levels in the EG Boiler/Economizer is about 14~16%, so this can supportcombustion.The nature of combustible deposits include soot from the combustion of fuel in the plant aswell as some amount of unburnt oil (fuel and lube oil), particularly at low loads.Ignition of soot may arise at sufficient high temperature of the layer of the soot whosesurface temperature may go up to 300~400

˚

C, but presence of unburnt oil may lower this

temperature to about 150˚

C and under favorable conditions to about 120˚

C.

SMALL SOOT FIRES: Mainly occurs during maneuvering with the engine being operated atprolonged low loads. The situation may arise even at short low load running if the fuel is bad.Indications:

a. High economizer exhaust gas outlet temperatureb. Sparks from the funnelc. Engine running parameters showing deviations due to increased exhaust back

pressured. High steam pressure or outlet temperature from the super heater section if fitted

How to deal with this situation:a. Stop the main engine so that the oxygen levels can be brought well below the fire

sustenance levelsb. Carry out the boundary coolingc. Fire watch to be kept on deck due to the risk of the funnel sparks, fire hoses to be

kept chargedd. Continue running the circulating water pumpe. Never use the soot blowers for fire fightingf. Stop the auxiliary blowersg. Ensure that all the exhaust valves are positively closed (check the spring air pressure)


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[email protected] the soot fire has now turned into metal fire (identified immediately by the loss of thecirculating water of the economizer), stop the circulating water pump. Carry out theboundary cooling.If means are provided, deluging the economizer fires with copious amounts of water shouldbe carried out to the seat of the fire. This is essential because, if lesser amount of water usedthe fire is additionally supported by the production of steam sourcing hydrogen for the

situation to get worse.

Hydrogen fire: Occurs because of dissociation of water (steam) into hydrogen and oxygen orcarbon in connection with carbon monoxide and hydrogenThis occurs only above 1000

˚

C

Iron fire: Oxidation of the iron at high temperature occurs at a rate sufficiently high to makethe amount of hest release from the reactions sustain the process. These reactions may takeplace at a temperature in excess of 1100

˚

C

124. How do you identify the symptoms of a crank case explosion? What actionwould you take to minimize the hazard?

a. Engine noiseb. Oil mist detector alarmc. High bearing temperature (alarm if fitted)d. In case of minor explosions the crank case relief door releases the pressure

ACTION:a. Slow down the engine, inform the bridgeb. Take permission from the bridge for stopping the enginec. Continue running the engine lube oil pumpsd. In severe cases, it is prudent to open the engine room skylights and other vents and

abandoning the engine room. The doors from the engine room to the accommodationshould be kept shut. Return to the engine room only after carrying out risk

assessmente. Turn the engine by turning gear with the indicator cock opened to prevent seizure ofthe hot spots

f. Stay clear of the crank case specially in the region of the relief door to theturbocharger suction

g. Don’t open the crank case door until sufficient time has elapsed

125. What are the various IG plant alarms and trips?

ALARMS:a. O2 content highb. Scrubber tower water level lowc. Deck seal water level highd. Deck seal water level lowe. IG pressure lowf. IG pressure highg. IG temperature highh. Boiler uptake soot level high (Ringlemann)

TRIPS:a. Scrubber tower water level highb. Venturi water pressure lowc. Low IG cool sea water pressure


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[email protected]. Scrubber cool sea water pump abnormal stope. Power failuref. Incorrect mode of the boiler (mode set to NAV, GF.. etc)g. IG temperature high high (more than alarm level)h. IG blower abnormal stopi. Deck seal water low flow

j. IG deck main extreme high pressure

126. Reciprocating pump is getting over heated, what checks should be carriedout?

a. Inlet and outlet valves are to be examinedb. Inspect the seat and lapping should be done if requiredc. Valve lift should be checkedd. Inspect piston and piston ringse. Spring (valves should be checked for tension and springing action)f. Liner wear down should be checkedg. Driving belt should be checked for wear down or damage

127. Explain the various rudder inspections and testing in the dry dock

a. Visual examination of the rudder plating for cracks and distortionb. Air plugs and drain plugs are to be opened in the presence of the class surveyor,

repair superintendent and chief officer. Water draining out indicates a breachedrudder and the breach to be located by air pressure testing and applying soapsolution, repairs to be planned

c. Check the rudder drop in the steering gear compartment (trammel gauge)d. Check the pintle clearances, jumping bar clearance and the palm coupling bolts

tightness to be checkede. Check the rudder stock for corrosion, erosion and any damagef. The inspection plates in the way of the upper, the lower pintle to be cut open, and the

pintle nuts checked for proper securing. Later the plates to be welded and tested.g. Hydraulic test the rudder for a static head of about 2.45m of sea waterh. After draining and re oiling the internals, plug the drain and check the effectiveness

by a vacuum check and cement the plugi. The rudder stock gland packing has to be checked and renewed

128 . What is caustic cracking or embrittlement? What is its cause? Suggestremedy

This is a form of intercrystalline/intergrannular cracking and occurs when a specific corrodentand sufficient tensile stress exists. Iron consists of ferritic granules bonded by iron carbide sothis gives a scope of the intergrannular corrosion. This can be found in water tubes, superheater, reheat tubes, and in stressed components of the water drum. The stress may be dueto thermal, bending or residual stress (due to welding). This usually occurs as a localizedattack in the combination of NaOH, some soluble silica and a tensile stress. The mechanismbegins with the accumulation of the corrodent NaOH due to –

a. DNB (departure from nucleate boiling)b. Depositionc. Evaporation at the water lined. Small leakagee. High heat flux (rapid evaporation)f. High pressure


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[email protected] corrosion below 149

˚

C or with NaOH concentration below 5% is rare. Increasedsusceptibility occurs at about 20~40%. This corrosion is difficult to identify in the beginningand ND testing has to be carried out at the suspected areas. At some time after the initialstart of the corrosion, this manifests as a whitish highly alkaline deposits or sparklingmagnetite.

COUNTER MEASURES:a. Applying heat treatment process to relieve stresses after fabrication/repairs (welding

etc)b. Correct and accurate boiler water treatmentc. Avoid DNBd. Avoid accumulation of the depositse. Prevent leakage of corrodentsf. Prevent carryoverg. Use of rifling in the water tubes

129. A shell & tube type cooler tubes are leaking, what is the procedure to rectifythe leaks?

Before jumping to any conclusions it is prudent to check where the leaks are from. It couldbe from the breach on the tube (a hole etc) or from the origination of small gaps betweenthe tube plate and the expanded portion of the tube. The procedure should to be based onthe findings.A holed tube should be plugged from both the sides; the plugs can be of cork, wood, rubber,brass, or copper as supplied by the manufacturer. Care should be taken when plugging withthe metal plugs, not to damage the tube plate.If the leaks are from the gaps between the tube plate and the tubes, slight flaring of the tubemay help preventing the leaks however this flaring, if excessive will damage the tube plateand also the tube itself. Alternative methods are available by carrying out surfacepreparation and applying metal repair putty, like Devcon’s brush able ceramic repair putty.

In the above process, if the plugging of the tubes is about 10% the tubes have to berenewed.

130 . Explain a tube renewal process

To remove the tube, first remove the flare on the tube by chiseling off the flare flush with thetube plate and then split the tube taking care not to damage the tube plate. The tube canthen be cut by a tube cutter to drop the tube inside the shell. Fitting of a new tube is carriedout by first positioning the tube in place between the end tube plates and flaring to thecorrect amount by a flaring tool after fixing the other end by a brass wedge. It could byeither hand operated, pneumatic or motor operated. The tube should have a protruding partabout 1/4”~1/8” and the flaring should be to about 1/8” + tube diameter at the tip.

131. What is a phosphate reserve? Why is it important in high-pressure boilers?

A reserve of phosphate should be present in the boiler water to neutralize any hardnesssalts, which may enter. These salts would deposit as a scale on the heating surface if reservewere too low while, too high a reserve leads to foaming and possible excess production ofsludge. It also gives alkalinity.


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[email protected]. The tell tale hole between the lap welding seams of the doubler plate / ring to be

checked for leaks in service to ensure that the internal welding is intactg. Face of the man hole is to be checked for pitting marksh. Drain should be cleari. All points of high stress and corrosion are to be thoroughly checked viz. welds,

supports braces, the bottom of the bottle where water/oil is collected. Pay attention

to the zone of water line. j. Check for leaks at the mounted valve glands/flanges, carry out inspection of the valve

face and seat for wire drawing effectk. A timing check with the air bottle completely charged and isolated will give a good

idea of the intactness of the pressure vessell. The safety/relief valve setting to be inspected as per the class requirementm. Regularly check the alarms and monitoring equipment for proper functioning

137. Explain the air bottle entry procedure

a. Inspection is to be carried out when the receiver capacity is not required formaneuvering

b. Receiver properly isolated, depressurized and notice pastedc. The internal pressure is to be checked by the pressure gauge and by opening the

drain valved. Open the manhole door carefully and ventilate the air bottlee. Obtain an enclosed space permit and comply with itf. Ventilation is to be maintained during the entire time of enclosed space entry

138. What action should be taken in case of corrosion/wasting observed on airbottle?

MINOR: clean the site of corrosion, observe the varnish manufacturer instructions for surfacefinishing prior applying the coat. Apply new coat of the varnish.MAJOR: The site has to be cleaned and revarnished as above. The air bottle has to be

derated.Incase of excessive the entire bottle has to be replaced.The derating procedure should be carried out as follows:

a. The extent of the derating is determined by the class surveyor to a value whichensures the safe limit of the hoop stress at this reduced thickness of the shell plating

b. The derating should not violate the starting air requirements for consecutive starts ofthe main propulsion engine

c. The setting of the safety/relief valve, should be set not exceeding 10% of themaximum working pressure after derating

d. The cut in and cut out pressure switches for compressor automation should bereadjusted

For these reasons the air pressure vessels on board ship are fabricated to allow for deratingin future still complying with the consecutive start requirements of the propulsion engine

139. What is a PV breaker? Why is it fitted?

This is a U tube manometer filled with an ethylene glycol solution (as a measure againstfreezing). The height of the manometer is manipulated such that the pressure on either sidemay displace the solution, into tanks incase of vacuum inside cargo tanks and outside on tothe deck incase of over pressurization inside cargo tanks. Usual set values of PV breaker are+1800mmHg on high pressure and -700mmHg on vacuum side.


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[email protected] breaker is fitted to the IG main line on the deck to protect cargo tanksfrom the following:

a. Abnormal rise of pressure in the cargo tanks which occurs when cargo is loaded withspecified rate and that all gas outlets are closed

b. Abnormal drop of pressure in cargo tanks which occurs when cargo is unloaded withthe rated capacity of the cargo pumps and the inert gas blower fails

c. Abnormal rise or drop of pressure in cargo tanks which occurs, when the breathervalves fails to operate properly for the fluctuation of the pressure in cargo tanks, dueto variation in atmospheric and sea water temperatures, altering the vapor pressureinside tanks

140. What is the routine maintenance, checks on the PV breaker?

CHECKS:a. Check the seal liquid periodically and replenish the liquid in case

• Liquid levels of inner and outer pipes do not coincide• “0” points of inner and outer pipes do not coincide when the pressure inside

the cargo tanks is atmospheric pressureb. Clean the flame screen in the cover at the top when the ships makes a dock-in

CHECKING PROCEDURE:a. Checking the liquid level of the inner pipe (open the vent cock located at most top of

the gauge, close the upper gauge cock and open the lower gauge cock) this is alsotermed as “bigger range”

b. Checking the liquid level of the outer pipe (close the vent cock, open the upper gaugecock also open the lower gauge cock) this is also termed as “smaller range”

Two distinct scales are provided for the liquid gauge one “higher” and other “lower” therespective readings (as in ‘a’ and ‘b’) should match numericallyMAINTENANCE & INSPECTION IN DRYDOCK:Disconnect and remove top cover with attached internal stand pipe. Disconnect and removeFlame Arrestor Assembly. Remove flame screen. Thoroughly clean internal of flame arrestor.Renew flame screen with shipyard supplied equivalent type mesh. Drain breaker liquid,

thoroughly clean internal breaker body, and stand pipe. Apply two coats of shipyard suppliedtar epoxy by hand brushing to all internal surfaces. Level gauges, cocks and protectivehousing to be removed and transported to workshop for cleaning and overhaul. Dismantlesight glass tubes and cocks for overhauling and cleaning. Upon completion, re-assemble andre-install onboard with new shipyard supplied approved type jointings, studs, and nuts.Prove filling and level cocks clear and free. Disconnect and remove PV Breaker valve.Dismantle and clean surfaces. Lap valve and disc. Set valve to +0.21kg/cm2 and0.07kg/cm2 in the presence of the attending superintendent. Record and submit calibrationof valve settings. Close on completion with new shipyard supplied approved type jointingsand sealing compound and bolts and nuts.

141. Explain the mounting arrangement of boiler feet

The alignment of boiler should incorporate provisions for thermal expansion at the boiler feet(saddles) when the boiler is in hot operating condition. Expansion may be in the order of10mm. Assuming a four-point support; one foot will be bolted down hard to the foundation,while the other three feet will be bolted down so as to permit the feet to slide.Holes for the fixed bolts will be reamed in place. The foundation bolts in way of the slidingfeet must be accurately located with respect to the elongated holes in the boiler feet toenable the feet to slide clear of the bolts. The pipe sleeves prevent the bolts from tighteningdown on the sliding feet. A brass liner or a lubricant such as molybdenum disulfide is


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[email protected] used to facilitate the sliding action. In some cases, the pipe sleeves are not used.Instead, the bolts are tightened only slightly so that the boiler foot can slide.

BOLT

ELONGATEDHOLE INBOILER FEET

FIXED FOOT

SLIDING FEETOUTLINE OF

BOILER

Interference body bolt or fitted bolt

FIXED FOOT

Lock Nut

Boiler Feet

Steel Liner

Foundation Bolt


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[email protected]

142. What is a fitted bolt?

The answer lies above. This is a closely fitted bolt. The holes are initially drilled to undersizeand are reamed in the assembling place before the bolts are tightened in place. Accuracy isrequired in the machining. These bolts could be of two types one having a slight taper ofabout 1:100 on diameter and the other having a large taper of about 1:15 on diameter.However, the holes in either case are reamed in final place.Some times an oversized bolt is stretched hydraulically reducing the bolt diameter. Whentightened down and the hydraulic pressure is released the final exact fit in the bolt hole isachieved, like a pilgrim nut on coupling shafts.These bolts find place in engine / boiler mountings, coupling shafts etc. and form a rigidfixture. On main engine mounting these are situated aft of the engine in the way of thrustblock. The foundation bolts towards the fore end (either side of the engine ‘P’ ‘S’) aregenerally simple foundation bolts which are not fitted bolts. This system of foundation boltsoffers the rigid seating with provision for thermal expansion towards fore end.

143. What is the material of main steam piping and explain how it is supported?

Main steam piping is usually made of seamless low alloy steel. Where temperatures areabove 455

˚

C, the most widely used alloy contains 0.5% molybdenum, 1.25% chromium.Gaskets between the flanges are made of thin stainless steel strips spiral wound withinsulating filler between successive layers.There are three types of supporting to carry the weight of main steam piping.

a. Rod hangersb. Variable spring hangersc. Constant force spring hangers

Horizontal sway braces are often used to resist dynamic forces applied to the piping due torolling and pitching or due to vibrations transmitted to pipe anchor points. Sway braces couldbe of the turnbuckle-rod type, the preloaded spring type or the hydraulically damped type.At fixed anchor points, the pipe anchor brackets are separated from the anchor foundationby insulating material to reduce the heat transfer from the steam piping to the hull structure.

144. Soon after complete overhauling a generator engine, its lube oil consumptionincreases. What checks do you carry out in this regard?

a. Check that the lube oil system valves are set back to normal, and that the concernedvalves are correctly holding

b. Verify dip stick bottom for any blockage which can give erroneous results


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[email protected]. Check for normal operation of the purifierd. Ensure that the piston scraper ring is set correctly, if this ring is boxed back upside

down, the oil scraping action of the ring is lost and uncontrolled lube oil enters thecombustion chamber. This presents a significant oil loss

e. Ensure that the cylinder head valves are correctly boxed back. Misalignment of thevalve spindle with their guide also causes lube oil to enter the combustion chamber

causing oil loss

145. Generator lube oil sump level increases, what are the checks you wouldcarry out?

a. Check that the generator lube oil systems valves are correctly positioned and that thesump filling valve is holding

b. Ask the personnel for if they have carried out any transfers just before, related to thesump oil of the generator

c. Check the purifier for correct operation and that no water is being discharged with thepurified oil

d. Change over the generator concerned, isolate it and check the sump for anycontamination like water. Basing on the findings further inspections can be carriedout, like checking the cylinder liner jacket cooling water sealing O-ring etc.,

146. How do you prepare a boiler for survey?

Before a survey, the boiler must be prepared. The preparation process involves:I. Water side preparation prior entry into the steam drum for internal inspectionII. Gas side preparation for external tubes inspection also the refractory condition can

be inspectedIII. Electrical isolation

Electrical side isolation:The power supply to the boiler control panel should be isolated. The power supply breakers

for the FD fan; burner pilot fuel oil pump should be switched off and caution tags put.Gas side/Exhaust side:a. If the boiler is an exhaust gas boiler, then the main engine should be isolated from

starting positively. The composite boiler should be isolated on the fuel side in additionby manual isolation of the fuel line by a shut off valve and isolating the power of theboiler control panel.

b. Oil fired boiler should be isolated on the fuel side by a manual shut off valve andisolating the power of the boiler control panel

Waterside isolation:a. The boiler should be taken out of service. With the boiler shut, isolate the boiler on

fuel/exhaust side electrical side and water side by isolating valves, power supplybreakers as the case may be

b. Empty the boiler of water by blowing down, after allowing sufficient time for the boilerto cool gradually to prevent excessive thermal shock

c. When blowing down to sea, open the overboard valve first then the boiler valve to beopened gradually. The nearing completion of the blowing down operation can be feltby falling noise, pressure. At this point, care must be taken not to let the coldseawater into the boiler. Start closing the boiler blow down valve when the boilerpressure is low enough, and when it is down to the desired value, the valve must beclosed down tightly and the ships side cock closed. This is to be done to keep out theseawater ingress positively even though the valves are usually of non-return type.


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[email protected]. Allow the boiler to cool down further and loose all its pressure, and when the boiler

pressure is at atmospheric pressure open the air cock and gauge glass drains toensure the pressure is atmospheric inside the boiler

e. Either the top door or the bottom door can be opened at this stage but not both,while removing bottom door care must be taken against any hot water if present cancause injury to the personnel near it

After the boiler has sufficiently cooled the access points can be opened, the spaces wellventilated, enclosed space entry/steam drum entry procedures should be followed.The fire/exhaust side should be cleaned after initial examination

a. Open access doors in way of the uptake and front and rear walls and the burnerregister and all hand holes

b. Hydro-jet all soot deposits on tubes. Allow for collection and disposal of fresh waterc. Mop up the fireside to dry. Neutralizing chemical can be added in order to avoid

corrosion. Heating lamps can be used to dry out the furnaced. Scrape hard deposits on all generating and water wall tubes, sweep and remove all

carbon, soot and debris on the furnace floor

The waterside requires a similar approach for cleaninga. Remove for access to steam drum and water drum manholes and headersb. Allow for header blanks for water side surveyc. Remove all steam baffle plates in the steam drumd. Hydro-jet cleaning of the internals of drums and tubes may be required to remove

mill scale and sediments

147. What are oxygen scavengers?

Oxygen scavengers are chemical compounds, which are added to the boiler feed water toeliminate oxygen residuals and to assist in the passivation of metal surfaces.There are a number of these chemicals available, and a selection is a function of the amountof oxygen present, risk, feed system design, economics and any particular limitations

required by the process using the steam.Some widely used oxygen scavengers are:a. Sodium sulfite (Na 2SO 3 )

Method of dosage : Dose the feed water continuously to maintain a desiredconcentration. Where corrosion in the feed system is experienced, it is used as acatalyzed form of sodium sulfite. The catalyst (usually a salt of cobalt) is to speed upthe following reaction, so that this is complete before the water gets into the boiler.How is O 2 Scavenged? : 2Na 2SO 3 + O 2 --------- 2Na 2SO 4Limitations : The speed of the reaction is influenced by the pH of the feed waterwhich should be between 8.0~9.5. Sodium sulfite adds some solids to the feed water,so it should not be overdosed or applied to the cold feed water. Otherwise, this maylead to increased blow down requirement.Sodium sulfite can be used in the boilers of pressures up to 62 bars. Above thesepressures, decomposition products such as H 2S and SO 2 can affect steam purity

b. Hydrazine (N 2H4)Method of dosage: Liquid hydrazine is injected at the earliest possible point in thefeed water system.How is O 2 Scavenged? : N 2 H4 + O 2 -------- N 2 + 2H 2OLimitations: Excess hydrazine should be controlled to avoid an undue rise in theammonia level in the steam; there is a danger of copper corrosion in the condensingplant. (Ammonia is produced by the decomposition of excess of hydrazine can providea suitable alkaline condition in the steam and in the condensate system,


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[email protected] 2 H4 -------- 4NH 3 + N 2 ). Hydrazine is not permitted in the systems where steamis in contact with the foodstuffs.

c. Carbohydrazide (Eliminox) (N 2 H3 ) 2CO)Carbohydrazide is a combined form of hydrazine. It is superior in performance and isdesigned to minimize exposure to hydrazine vapors during handling. Carbohydrazidereaction products will add no dissolved solids to water. This can be used as an oxygen

scavenger and a metal passivator at both high (230oC) and low (60

oC) temperatures.

Carbohydrazide can be applied to boilers up to 170 bars.How is O 2 Scavenged? : (N 2H3 ) 2 CO + 2O 2 -------- 2N 2 + 3H 2 O + CO 2Limitations: in boiler, Carbohydrazide decomposes to hydrazine as one of theproducts, so it cannot be used in systems where the steam is used for humidification.(FDA rules)

d. TanninsCertain alkaline tannin solutions have good oxygen absorbing capability. A 6ppm ofcertain tannins extracts can remove 1ppm of oxygen at a pH of 12. The oxygenscavenging efficiency is better than that of sodium sulfite.

e. Erythorbic Acid (Sur-Gard) (R 1-C(OH)=C(OH)-R 2) This is an effective oxygen scavenger and a metal passivator. This is the only non-volatile scavenger, which can be used for spray attemperation. This does not addmeasurable solids to the boiler water; is non-volatile and will not hamper the steampurity. Erythorbic acid can be used in boilers up to 122 bars. This is considered as asafe substance by FDA.How is O 2 Scavenged? : R 1-C(OH)=C(OH)-R 2 + ½O 2 -------- R 1-(C=O) 2-R 2 + H 2 OLimitations: Ammonia is produced in the boiler as a by-product. This is notrecommended for use for boiler lay-up. Good corrosion control requires a high boilerwater pH value since the magnetite film is at its most stable condition when the pH is10.5~11.5.

147. What are the various control actions?

The basic controller actions can be grouped as

a. Two position or on-off controllersb. Proportional controllers: It is also called corresponding control. The corrective actionof controller, C, bears a constant ratio to the error θ = ± (Measured Value – DesiredValue), Thus C = -K θ (where K= constant of proportionality)

c. Integral controllers: It is also called the reset action control. The rate of change ofcorrective action is proportional to the error. Mathematically, dC/dt = -K θ orC= -K ∫θ dt + k (where K= constant of proportionality, k= constant of integration, C=control action)

d. Derivative controllers: It is also called the rate action control. The amount ofcorrective action is proportional to the rate of change of error. It is never used aloneand is always used in conjunction with the integral and or proportional controllers. Aswith a constant error, the control action being derivate becomes zero. C = -K d θ /dt,(K= constant, C= control action)

e. Proportional-plus-Integral controllers f. Proportional-plus-Derivative controllers g. Proportional-plus-Integral-pus-Derivative controllers

148. How is the chain drive of a main engine inspected?Chain inspection is to be carried out as follows:

a. Make a general inspection for loose screws and boltsb. Inspect lube oil pipes for damage, and check oil jet nozzles for possible stoppages or

deformations


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[email protected]. Examine the rubber track of the guideways for cracks or other damage, replace the

guideway bits if they have started to be plucked out of the rubber stackd. Check the teeth of the chain wheels. If abnormal wear is found, take a measurement

by placing a straight edge over the wear edges and measure the length of the wearalong the straight edge and the gap between the straight edge and the wear trough

e. Check the chains for cracks on possibly defective rollers and side plates

f. Check that for each chain link, chain rollers can run freely and that the chain links canfreely move on the pin and bushing

g. Check the chain wear by measuring the length of 10 chain links and compare theresult with the value in the data provided by the maker. If the parameter showsabnormality then adjust the chain tightener

149. Explain the procedure of chain tightening[ Courtesy MANBW ]

a. Loosen the nuts A, B, C and D to free thechain tightener bolt b. Turn the engine so that the slack part of the

chain is on the same side as the tightenerwheel. If balance weights are mounted, turnthe engine so that the weights hang verticallydownwards

c. With the balance weights in this position,tighten the nut B on the chain tightener boltuntil there is a clearance of 0.1mm betweenthe shaft and the nut . then tighten the nut Bto a tightening angle of about 720 o

d. Tighten the nut C hard against the contact face of the shaft. Tighten the nut D, locknuts A and B with the tab washer

e. Measure the distance X, if the chain is worn (i.e. X>165mm) repeat the procedurefrom ‘a’, but tighten the nut B only to a reduced tightening angle 600 o .

f. If the distance exceeds the maximum distance 265mm, find and eliminate the causeof this abnormal chain elongation, like a defective chain, damaged chain wheels orbearings etc., repeat the procedure from ‘a’.

g. Repeated tightening of the chain will gradually alter the cam angle in relation to thecrankshaft. It is therefore necessary to readjust the camshaft to its initial angular


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[email protected] after the lead angle has been increased by 2 o . The camshaft is adjusted byturning both halves at the coupling joint with the chain wheel

150. Why is a copper gasket annealed?

The essential qualities of a copper gasket are softness and toughness (provision for cold

working without fracture). In its place the copper gasket is subjected to considerablemechanical stress, resulting from elastic strains internally balanced. These elastic strains aredue to jamming of dislocations, which occurred during cold deformation (during service). Ifthis cold worked gasket is heated to a sufficiently high temperature the total energy availableto the distorted regions will make possible the movement of atoms into positions ofequilibrium so that the elastic strains diminish and the locked-up energy associated withthem ‘escapes’. Tensile strength and hardness will fall to approximately their original valuesand capacity for cold work will have returned.

151. What is the difference between a safety valve and a relief valve?

A safety valve is a pressure relief valve actuated by inlet static pressure and characterized byrapid opening or pop action.A relief valve is a pressure-relieving valve actuated by inlet static pressure and opens inproportion to the increase in pressure over the opening pressure.The terms ‘safety’ and ‘relief’ are synonymous; the safety valve is generally applied to valvesprotecting any vessel, which could explode and endanger life whereas the relief valve is moreappropriate to the valve protecting system containing non-expansible liquid a burst causingno violent explosion.Another notable difference between these valves is that the vent of a safety valve is led to a

‘safe’ place (harmless to the working personnel) whereas a relief valve vents just outside thevalve.

152. What are the parameters of a lube oil analysis?

The parameters of a two stroke, heavy fuel oil engine circulating/system lube oil area. Specific gravity: Range 0.90~0.98. This is used for identification of the oil. Limits: 5%of initial value

b. Viscosity: Viscosity increases with oxidation, contamination with cylinder oil, heavyfuel or water. Diesel fuel contamination decreases viscosity. Limits: Max 40%, Min -15% of initial value

c. Flash point: Gives an indication of possible dilution with diesel oil. Limits: Minimum:180

˚

Cd. TAN (total acid number): Expresses the total content of organic and inorganic acids in

the oil. Organic acids are due to oxidation products. TAN = SAN + weak acid number.Limits: TAN 2

e. SAN (strong acid number): This expresses the amount of inorganic acids in the lubeoil. Inorganic acids are usually sulfuric acid from the combustion chamber orhydrochloric acid arising from seawater. This will be stated. SAN makes lube oilcorrosive (especially together with water) and should be zero. Limits: SAN = 0

f. Alkalinity/TBN (total base number): Gives the alkalinity levels in the lube oilcontaining acid neutralizing additives. Limits: High = 100%, Low = -30

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