Friday, April 24, 2020

Capacity control operation

 Loaded operation : 
A rise in suction pressure causes needle valve to close. Oil pressure in the power element increase as the oil enters capacity control circuit from the oil pump. Power  element piston is forced upwards , pivoting lifting fork downwards .  Lifter pins drop  allowing suction valve to  seat & load control the cylinder.

Unloaded operation  : 
A drop in suction pressure causes the needle valve to open. Oil bleeds through the valve to the crank case decrease the oil pressure in the power  element, hence the piston moves downwards. lifting fork is pivoted upwards moving the lifting pin upwards. Suction valve is raised from its seat & controlled cylinder is unloaded. 

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Criteria for re use or replacement of Aux engine connecting rod

The power generated by the piston in the combustion chamber of marine engine is transferred to the crankshaft using the connecting rod. While transferring this tremendous power, the connecting rod itself is subjected to different stresses, which makes is vulnerable to damage. For this reason connecting rod bolts are used to join the connecting rod and con-rod bearing cover under the tremendous stresses generated by the running engine.
The most common type of connecting rod that is used in the ship’s auxiliary engine is oblique or cross-cut connecting rod which is made of two parts.
The connecting rod of the engine must be inspected at regular intervals of time to ensure there is no defect or problem to avoid any future accidents/emergency. It’s the knowledge and skills of the engineer that decides whether to use the same connecting rod or to renew it with the spare one.
Following points must be considered when checking the connecting rod for re-use or replacement:
1. Check the ovality of the connecting rod: Check the ovality of the connecting rod by tightening both parts at its rated torque. Inside micrometer is used to determine the correct and current ovality of the connecting rod. If the ovality is out of limits, the connecting rod is not to be reused.



2. Check connecting rod for fretting and corrosion: Connecting rod to be checked for fretting and corrosion. If fretting is small, it can be removed by using oilstone. Never use grinder or scrapper for this purpose. Con-rod with severe fretting and racks must be discarded.
3. If connecting rod with fretting is to be used, check for cracks: Minute fretting can be tolerated over the connecting for reuse only if the surface does not have any cracks. If the fretting is in small area and oil stone is used to treat the same, the complete area must be checked again by using magnaflux which detects small hairline cracks which are not visible to the naked human eye.
4. Check cracks between connecting rod and bearing cover: The serration and bore between connecting rod and bearing cover to be checked for cracks by using die penetrating
5. Renew connecting rod and connecting rod bearing cover together:Connecting rod and connecting rod bearing cover to be renewed as a whole. Never renew single part of the connecting- rod in case of damage as the serrations are machined in pair to locate the two halves relative to one another.
6. Re-machining of serrations should not be done: Re-machining of serrations of connecting rod /bearing cap or bore should not be done even if there is minute damage or indentation
crack detection test. Rod to be used only when there are no cracks detected. If there are small cracks in the connecting rod bearing cap serration, renew it with new spare one.

7. Bearing shell with fretting at its back should not be used: Bearing shell with fretting at it’s back side must not be used with connecting rod and it is to be renewed in set.
8. Ensure bolts and bearings are of same type during replacement: If the connecting rod is replaced, it should be of same type and same con-rod bolts and bearings to be used. Ensure to read the older generator data to confirm the bearing size (undersize or oversize) to be fitted while renewing the shell.
9. Replace Connecting Rod Bolts in Sets: Connecting rod bolts to be used and replaced in sets. If the connecting rod is renewed with the spare one, the con-rod bolts from the old con-rod must not be used with the new spare connecting rod.
10. Correct sequence and tightening torque: Once it is decided to reuse or replace the connecting rod, the engineer office must ensure that he knows the correct assembling sequence
(front/ back side, pair of con-rod and bearing cap etc. ) and rated tightening torque is applied on the con-rod bolt with step- by-step tightening procedure as listed in the manual.
The assessment of connecting rod for reusing/ discarding is a critical decision to make for the ship’s engineer officer. A slight mistake in making the correct choice may lead to major generator damages and sometimes even causality.
The above mentioned are some of the important basic checks which should be performed by the engineer to upkeep the generator’s long life and efficient performance

Rudder wear down

This refers to the measurements taken generally during a docking period to indicate excessive wear in the steering gear system particularly the rudder carrier. The significance of this is that for ram systems excessive wear can lead to bending moments on the rams. For rotary vane systems it can lead to vane edge loading.The readings taken are offered for recording by the classification society.
TrammelThis takes the form of an 'L' shape bar of suitable construction. When the vessel is built a distinct centrepunch mark is placed onto the ruder stock and onto a suitable location on the vessels structure, here given as a girder which is typical. The trammel is manufactured to suit these marks As the carrier wears the upper pointer will fall below the centrepunch mark by an amount equal to the wear down.




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Babbitt metal

Babbitt metal, is an antifriction metal alloy first produced by Isaac Babbitt in 1839. In present-day usage the term is applied to a whole class of silver-white bearing metals, or “white metals.” These alloys usually consist of relatively hard crystals embedded in a softer matrix, a structure important for machine bearings. They are composed primarily of tin, copper, and antimony, with traces of other metals added in some cases and lead substituted for tin in others.
Bearings used in large marine diesel engines are tin based babbitt metals. Lead content is a minimum. Tin based white metals have 4 times the load bearing characteristics and two and a half times the maximum surface speed of lead based white metals.

Tin-based white metal is an alloy with minimum 88% tin (Sn), the rest of the alloy composition is antimony (Sb), copper (Cu), cadmium (Cd) and small amounts of other elements that are added to improve the fineness of the grain structure and homogeneity during the solidification process. This is important for the load carrying and sliding properties of the alloy. Lead (Pb) content in this alloy composition is an impurity, as the fatigue strength deteriorates with increasing lead content, which should not exceed 0.2 % of the cast alloy composition. Tin based white metal is used in the main bearings, crankpin bearings, crosshead bearings, guide shoes, camshaft bearings and thrust bearings because of its excellent load carrying and sliding properties.

Babbitt metal is soft and easily damaged, and seems at first sight an unlikely candidate for a bearing surface, but this appearance is deceptive. The structure of the alloy is made up of small hard crystals dispersed in a matrix of softer alloy. As the bearing wears the harder crystal is exposed, with the matrix eroding somewhat to provide a path for the lubricant between the high spots that provide the actual bearing surface.

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Interpretation of ignition quality of fuel from fuel oil analysis report

Interpretion of ignition quality of fuel from the fuel analysis report.

CCAI is an empirical attempt to estimate how long the fuel will take from injection to ignition and by implication the likelihood of engine damage. Knowing the CCAI, the operator must then judge the acceptability of that fuel for effective operation in the engine. Ignition quality can to some extent be
predicted by calculations based on viscosity and density, using formulas or graphs issued by the oil industry (CCAI by Shell or CII by BP).


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Fire prevention in drydock / port

    ➢    Machinery spaces are particularly vulnerable to fire hazards and casualties when large number of shore workers and their equipment are on board.
    ➢    Temporary electric connections ( like, lighting and power cable ) if not in proper order ( say, improperly connected or fused, having deteriorated insulation or being subjected to chafing from port holes or doorways ) can cause hazards.
    ➢    Air hoses passing through port holes and doors prevent them closing incase of emergency.
    ➢    Carelessness during welding or gas cutting operations may cause shower of sparks, resulting ignition of oily waste and oil.
    ➢    Minor or serious fires originate in oily rags and waste, rope and rubbish, lagging etc. in insulated spaces which may have smouldered for hours following ignition from cigarette end or sparks from electrodes or burning operations.
    ➢    The consequence of machinery space fire in port are severe because of large number of persons in the machinery space, their unfamiliarity with the ship and the probable inadequacy of the escape. It is essential that entrances are not restricted.
    ➢    On arrival dry dock, fire hoses from shore main should be connected fore and aft to the ship’s fire main through shore coupling.
    ➢    Smoking is permitted only in controlled stations.
    ➢    Arrangements such as blanking off or locking the operating mechanism of the C02 system, must be made to prevent the inadvertent release of smothering gas into machinery spaces.
    ➢    Communications and liaison arrangements should be made between ship & shore side officials.
    ➢    Ensure that precautions are compiled with –

            ▪    Temporary wiring is protected against chafing and is not overloaded,
            ▪    Adequate fire appliances are available,
            ▪    Access for shore fire fighters are adequate,
            ▪    Control center for external communications is established as a focal point for patrol man and the siting of breathing apparatus, axes and keys to locked spaces.

 When a fire occurs on board ship in port, the fire brigade must be called immediately no matter how small the out break. They will wish to be met at the gangway by a responsible officer who can act as a guide and provide as much as possible of the following information :
    a)    Where about of the fire,
    b)    Means of access,
    c)    Details of cargo together with stowage plan,
    d)    Ventilation arrangements,
    e)    Stability data,
    f)    Any person missing,
    g)    What fire fighting steps have been taken,
    h)    Condition of ship’s service,
    i)    Details of fixed installation, fire zones and general arrangements.

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Relief valve blow down ring

The difference between the set pressure at which relief valve starts lifting and at the pressure it reseats is known as blown down of relief valve . Suppose relief valve set pressure is 30 bar
At 30 bar it starts opening as pressure increases valve opening increases . When it drops to 28 bar valve reseats so blowdown is 2 bar.
The blowdown ring on a relief valve is adjusted to set te reseat pressure of the valve
The spring pressure determines the pressure at which valve coil lift , where as blowdown ring determines when it will reseats.

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Engine is running and how will take control from bridge to local

In MAN B&W there is a forced take over button in the local control panek where you can take direct control to local panel form any control position
How control is taken from Bridge to ECR
    •    Adjust (match) the telegraph to same speed
    •    Start increasing fuel lever (At this moment we can see deviation is coming down)
    •    When the deviation is zero then change the control to ECR .Bridge also have to accept the same time

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Virtual Tappet

 Like Aux engines which have a manual tappet to adjust , there must be a tappet clearance for the main engine as well. But with the absence of a rocker arm and spring – adjusting is not possible
In other words there is no real tappet for main engine
The exhaust valve is actuated hydraulically by oil from a hydraulic pump and is shut by spring air , when the spring air pressure exceeds the hydraulic oil pressure , This happens when the roller ( of the pump that is actuating the hydraulic valve ) is resting on the base circle of the cam
There is a valve called a throttle valve that is fitted on the hydraulic pump unit ( which actuated the opening of the exhaust valve)
When the system is just put into use the oil is relatively cold . After some time of operation the oil heats up and expands .This additional oil can make the exhaust valve stay open – leading to reduced Pcomp ,Pmax , reduced power and burning of the valve seat.
In order to prevent the valve being open due to the expansion of the hot oil , the throttle valve bleeds  off a small quantity of oil each time it closes.
If the throttle valve bleeds off too much the valve can bounce shut, thus damaging it . This adjustment of the throttle valve bleeds off the quantity if called “ VIRTUAL TAPPET “
Correcting setting of the Virtual Tappet ensures positive closing of the valve in a smooth manner without bouncing.

THROTTLE VALVE: It is a needle valve , at bottom of the cylinder . This is compensation for leakages which can occur in system . It is usually set by builders and adjusted at a trials .Tightening the throttle screw reduces the leakage amount and vice versa.
If leakage is small . then the amount of pressure generated within the high pressure line will be more .This will cause the exhaust valve to open earlier and close later , then intended .To certain degree it will increase SFOC  and thermal load on valve seats will also cause deterioration of the dead slow performance .To compensate for this the throttle valve will be opened and bleed oil from the system
If the leakage increases (If the total leakage amount coming from the throttle valve and hydraulic system exceeds a certain quantity ) the pressure in the high pressure line falls too quickly the valve will knock while closing .Pressure impact can also appear in hydraulic system when the valve is opening  .This increase in the impact can increase seat indentation damage . In this case throttle valve should be closed to prevent this noise and damage
The optimum setting of throttle valve , is when the exhaust valve just begins to knock and then closed in further 30 degree adjustments should be made with engine at 75 % load plus . If the exhaust valve does not  knock , with the fully open throttle valve , this means that hydraulic system is  completely sealed ( no leaks at all) the throttle valve in this case should be turned to 150 degree open

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Tuesday, April 21, 2020

Causes of overheated piston

  • Inadequate or failure of coolant supply and excessive deposit in cooling gallery.  
  • Continued overload operation  
  • Unbalanced cylinder load 
  • Incomplete combustion owing to loss of compression, faulty fuel timing, unstable fuel and insufficient charge air.  
  • High friction on liner owing to failure of lubrication, faulty rings conditions, long skirt touching the liner due Misalignment of piston and distorted liner 
  • Late ignition faulty fuel timing  
  • Excessive water content in fuel.  
  • Faulty rings conditions causing blow-by  
  • Long skirt touching the liner due Misalignment of piston and distorted liner  
  • Excessive deposit in cooling gallary

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Causes and signs of liner crack

Sign of liner crack
  • Fluctuation of pressure and temperature of jacket C.W system  
  • F.W coming out from the scavenge drains  
  • Overload at that particular unit (high in exht: temp: and Jacket temp)  
  • Expansion tank foaming
 
CAUSES
  • Due to rapid contraction of metal  
  • High difference in Jacket water (working) temperature  
  • Insufficient cooling  
  • Over tightening of cylinder head bolts 
  • Design failure 
  • After effect of immense Scavenge fire  
  • Due to loosened out foundation chocks resulting tie bolt slackening and Hoop Stresses on Cylinder liner increases  
  • Due to very high injection viscosity

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Reason for max linear wear on top and near scavenge ports


Reasons for maximum wear at top of the stroke being:
  • The gas load behind the ring is maximum  
  • It is the hottest region  
  • Viscosity of oil film is low and liable to breakdown under heavy load and high temperature  
  • Abrupt Change in direction of piston rings, at dead ends of reciprocating motion. 
  • Corrosive wear  
  • More liable to be attacked by acids.

 
Reason of maximum wear around the ports.
  • Due to leakage of hot gases past the top ring into the ports and these hot gases will tend to burn off the oil film.

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If no TDC mark on flywheel, How will you check pump timing?

IN MAIN ENGINE

  • Make a marking between cross head and guide Shoe while they are before TDC and also mark at the flywheel.  
  • Turn the crank shaft in the same direction until the crosshead and guide shoe are at the previous mark (coincide) 
  • Make the second marking on the fly wheel. We got two marks on the flywheel mid point between the two points is TDC.  
  • I will divide 360C around the flywheel.

  IN AUX ENGINE
  •  Remove the fuel valve  
  • Insert the rod onto the piston (mark on rod and flywheel)  
  • Turn crank until the rod previous mark  
  • Make the second marking on the fly wheel  
  • Mid point between the two points is TDC

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Sunday, April 19, 2020

Exhaust tunning

Exhaust tunning means by arranging the exhaust pipes with suitable length and suitable
valve timing to exhaust into the same pipe without disturbance.
When the exhaust valve of a diesel engine opens, the cylinder rapidly expands, and gain
velocity and kinetic energy as they pass into the exhaust pipe.
The kinetic energy of the mass of exhaust gas carries it along the exhaust pipe, and causes
a pressure build up ahead of the mass of gas and a partial vacuum behind it. This principle is  used in a tuned exhaust system. The partial vacuum created by exhaust from one cylinder is used to help exhaust expulsion from the following cylinder.
Grouping of exhaust pipes depends upon the firing order, length & diameter of exhaust pipe.

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Under piston pressure

  • Is a type of constant pressure charging system  
  • Air charged by T/C is passed through CAC into first stage manifold, and then through non return valves into second stage and under piston space  
  • In down stroke, piston under side compress further the scavenge air  
  • Differential pressure shuts the inlet non-return valves as scavenge ports are uncovered, and a pulse effect is given to cylinder  

Advantages
  • Assist tangential swirl and ensure complete evacuation of remaining exhaust gas  
  • No auxiliary blower may be required, during manoeuvring

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Pilgrim nut

  • The pilgrim nut provides a predetermined grip between the propeller and its shaft.  
  • The propeller boss is fitted with a S.G cast iron internally tapered sleeve, which is secured (fixed firmly in position) into the boss. This sleeve is bedded to the shaft cone before mounting in the  boss so that better fit is achieved which, combined with the pilgrim nut push up, ensure a good  friction grip. No key is required.  
  • The pilgrim nut is a threaded hydraulic jack, which screwed on to the tailshaft. A steel ring  receives thrust from a hydraulically pressurised nitrile rubber tyre. This thrust is applied to the  propeller to force it onto the taper sleeve.  
  • Propeller removal is achieved by reversing the pilgrim nut and using a withdrawal plate, which is fastened to the propeller boss by studs. When the tyre is pressurised the propeller is drawn off the taper.  

Advantages
1. The sleeve has a similar thermal expansion to the steel shaft, thus reducing the risk of
slackness in hot water.
2. An extension to 5 years survey period is allowed by classification societies.
3. The boss stress are reduced.
4. The cast iron/ steel contact has a higher friction coefficient than bronze/ steel.

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Action to be taken if OMD alarm gets activated

  • Inform to C/E  
  • Inform to bridge, take the permission to stop the engine  
  • Gradually reduce the engine and then stop.  
  • Cooldown the engine.  
  • Check the inside parts of the crankcase inspection.  
  • Made necessary repaired.  
  • Reset O.M.D and start engine  

Actions after receiving alarm from OMD
  • Note the position of the crankcase chamber having hot spot pointed by the sampling knob.  
  • Operate the selector button; turn the sampling valve knob to zero position or zero check, alarm should stop. 
  • Operate the check button the meter should swing on the scale and alarm should sound / operate  
  • Release the selector button, if the alarm comes from the same crankcase channel then it is confirmed that the alarm is not false.

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Oil mist detector maintance

  • By check zero adjusting or Send to shore 
  • Dailycheck alarm system
  • Clean measuring tube & reference tube  
  • Adjust the mirror  
  •  Check the lamp  
  •  Check the blower fan efficiency
  • Check rotating selector v/v performance
  • Clean sampling pipes.

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Need for breather pipe in crankcase


  • It is fitted to prevent crankcase explosion and to reduce pressure build up in it. 
  •  It maintains the pressure level in the crankcase about 25mm of water below the atmospheric  

FO settling /service gas freeing procedure

  • Drain down the entire charge into the double bottom tank through the dumping valve. 
  • When the tank is empty, open the manhole door which located one on top and other on side.  
  • Make force ventilation by blower fan through the manhole door at least 24 hrs.  
  • Then check the tank atmosphere by Davy’s safety lamp.  
  • If the flame burns clearly, the tank atmosphere is free from explosive or fatal gas.  
  • Enter into the tank and clear the sludge and wipe out with cotton rags. During entering the  tank ventilation must be provided continuously.  
  • One competent person must stand near the entrance to keep on wa
  • Use spark proof torch and lamp. Naked light and smoking not allowed in the vicinity

Davy's safety lamp

  • To detect the tank atmospheres, whether it is explosive gas or fatal gas.
  • It can get verify roughly the tank is gas free or not.  
  • It is required to apply directly into the required tank.  
  • Based on the ordinary fire process.  
  • No need to highly skill.  
  • But it required careful handling.

Extinguishing engine control room small fire

In E/R control room electrical fire breaks out, we must use CO2 portable fire
extinguisher, because CO2 is electrical nonconductor.
01) First give the fire alarm signal.
02) Check the condition of fire and cut out the power if is possible.
03) Shut off E/R ventilator and close the E/R entrance door but one exit door must be opened behind me.
04) Take CO2 portable extinguisher and fight the fire by staying up steam of air and the
distance about 3-4 ft from fire.
05) Move back to the exit door.
06) Leave the extinguisher and close the exit door.

Air bottle pressure test

  • Gag the relief valve  
  • Close all openings  
  • Fit test pressure gauge  
  • Remove filling valve and fill F.W completely  
  • Air purge and connect hydraulic pump at filling line.  
  • Apply pressure 1.5 times of working pressure and maintain at least 30 min  
  • Check leaking points.

Manually starting of Main Air compressor

  • Change the switch to manual position on the switch board.  
  • Check the L.O sump level and condition
  • Open the moisture drain valve. 
  • Open the compressor discharge valve & charging valve of air bottle.  
  • Open cooling water system valves.
  • Turn the compressor flywheel by hand (one turn).  
  • Start the motor, after draining the moisture shut the drain valve.  
  • Check the motor ampere consumed.  
  • Check the pressure gauge readings.  
  • Frequently drain the moisture.  
  • When charging full, open drain valve and stop the compressor

Liquid coagulant

It is more molecular wt colorless solution, such sodium aluminates, starch, terming, and resin.
Once being dose into the boiler water floating solid parti

Marking on safety valve

  • Manufacturer’s name  
  • Serial number  
  • Inlet diameter  
  • Operating pressure  
  • Discharge capacity  
  • Safe working pressure  
  • Blow off pressure

Boiler safety valve setting

  • Take standard pressure gauge (approved by surveyor) for accuracy.  
  •  Fill up water up to ¼ of gauge glass level, and shut main steam stop valve, feed check valve. 
  •  Without compression rings, hoods and easing gears, reassembled the safety valves with  spring compression less than previous setting.  
  • Raise the boiler pressure to desired blow off pressure.  
  • Screw-down spring compression nuts of any lifting valves, until all are quite.  
  • Arrange to have the desired steam pressure  
  • Adjust each valve in turn: 
a. Slacken compression nut until the valve lifts. 
b. Screw-down compression nut sufficiently enough, so that when the valve spindle is
lightly tapped, valve return to its seat and remain seated
c. Measure gap between compression nut and spring casing. 
d. Make a compression ring equal to this gap, and insert under compression nut. 
e. Gag the spindle of this safety valve, to prevent opening, while remaining valve is being
set. 
  • Remaining valve is again set and insert compression ring.  
  • Remove gag and retest both valve to lift and close together.  
  • Cap, cotter and easing gear to be refitted  
  • Caps and cotter pins padlocked to prevent accidentally altering the setting.  
  • When the surveyor satisfied the setting pressure, easing gear should be tested. 
All safety valves set to lift at not greater than 3% above approved working pressure (design
pressure)

What happens if no test and treatment is done to boiler water

  • Reduction in boiler efficiency due to poor heat transfer
  • Reduction in tensile strength  
  • Reduction in factor of safety 
  • Overheating of metal resulting distortion and eventual failure  
  • Increase in fuel consumption  
  • Excess concentration of NaOH (caustic soda) may cause caustic embrittlement on boiler metal  and tend to failure of boiler metal
  •   Corrosion  
  • Scale formation 
  •  Foaming, Priming, carried over (due to increase T.D.S level, foaming is present and tend to carried over and priming)

Action to be taken if intermediate bearing temperature increases

Overheating of plumber block bearing can be reduce by following ways 
  • By applying maximum lubrication  
  •  By applying maximum cooling  
  • By reducing to suitable engine speed.  
  • By applying the air
  •  By removing the cooling outlet pipe  
  • By filling the L.O into the sump at the same time open th

Cavitation erosion

  • Severe damage to complete bearing area.  
  • Cavities are usually around at low pressure areas i.e. oil groove or oil holes.  
  • Caused by an implosion of gas or air bubbles released from a lubricating oil film under particular  conditions  
  • The pressure set up locally during theses implosions are very high , possibly 220 bar & may cause  a pitting / cavitation
  •   Prevention – May be reduced by viscous oil because of damping effect high viscous oil &  viscosity must be in limit.

Bearing clearance methods

Bearing Clearance Methods: 
It is important that regular checking of bearing clearance is carried out, as the clearance
determines the effectiveness of lubrication. 

Lead wire
 Traditional method, but requires that bearing are tightened just to obtain
clearance. Accurate as long as load is not over squeezed. Lead is not to squeeze blow 1/3rd of  original diameter. 

  • Turn the crank shaft and set the crank at TDC position.  
  •  Remove locking arrangements, mark the nut position. 
  • Slacken the nut and lower the bottom half with bolts.  
  • Then three lengths of lead wires would be laid circumferentially in the bottom half at three  places
  • Place the bottom half into position and tighten the nut to its tightening torque.  
  • Lower down the bottom half again.  
  • Remove the lead wires and take the measurement.  
  • It must have within the limit, if out of limit, the bearing shell must be replaced with new ones or  readjust the clearance by adjusting shims.   

Feeler gauge
Quick method, but more difficult to be accurate when using the long feelers 
as measuring point may not be the minimum point.
  • Turn the crank shaft and set the crank at BDC.  
  •  Insert the feeler gauge between lower half and crank pin.  
  • Take the measurement readings. 

Plastigauge
Relies on the width of a plastic strip after compression. More accurate than
leads.

Bridge gauge
Depends on bedplate condition and crankshaft rigidity
Bridge gauge is an instrument for main bearing wears down measuring. 
  • Remove the lube oil supply pipe.  
  •  Remove upper bearing half and fit the bridge gauge.  
  • Then take the measurement by inserting feeler gauge.

Micrometer
More accurate

Crosshead Bearing Construction Features. 
  •  Thin shell bearings are used and bearing on either end of crosshead pin. 
  •  No shim used with thin shell bearing 
  •  Oil grooves or gutter used on bottom half to distribute oil. 
  •  Grooves do not extend to end and grooves are small because of loaded half. 
  •  Grooves to be limited otherwise reduce bearing surface. 
  •  Lubricating oil is directly supplied to crosshead bearing 
  •  Bearing material usually Sn-Al with Pb-Sn overlay.  

Crosshead Bearing Working Condition 
 High sudden load – Effect of combustion is directly on bearing
High bearing pressure – Bearing is placed high in engine. - Space limitations. – Assembly  reciprocating.
Diameter & length – Diameter & length of bearing are low. – Bearing area limitations. –High  specific loading
Possibility of bearing distortion – Bending moment & deflection are maximum at center. Pin  bored at center (earlier model engines). Less stiffness & high stress concentration. – Bearing
surface deflection. – Alignment difficulty.
Lubrication – Unsatisfactory or difficult oscillating moment. – Con rod swings over 25° -30°. 
Oil supply disturbed – Difficult smooth & uninterrupted oil flow.
 2 stroke engine – Unidirectional load.

Nip

The external circumference of a pair of bearing shell is slightly larger than the bore of housing.  The difference is called nip.

Cylinder lubricator quills O/H

01) Remove nut on lubricator quill (L.O connector) 
02) Take out lubricator quill fitted directly to the cylinder without passing through the jacket cooling  space.
03) Remove lubricator quill (L.O outlet side) 
04) Take out spring and non return ball valve. 
05) Clean all parts in diesel oil.
06) Check non return valve for occur. 
07) Check spring tension. 
08) Place the non return valve and spring into the lubricator quill then tighten out. 
09) Fit the lubricator quill to the cylinder tighten the nut. 
10) After fitting the lubricator quill, It is operated by hand at the same time check the cylinder liner wall  for sufficient oil come out.

Types of lubrication

Hydrodynamic lubrication (full fluid film) 

(1) Moving surfaces are separated completely by the pressure of a continuous unbroken film or a  layer of lubricant, generated by the movement of the two surfaces relative to each other. 
(2) Essential requirement is formation of a wedge of lubricants between surfaces. 
(3) Thickness of film 0.025 – 0.10 mm. 
(4) Lubrication for Journal Bearing, Bottom End Bearing, Tilting Pad Thrust Bearing

Boundary lubrication 

(1) It exists when a full-fluid film lubrication is not possible. 
(2) The sliding surfaces are separated by only a thin film of lubricant. 
(3) High friction between the surfaces and some degree of metal to metal contact occurs 
(4) Lubricant oil film decreases, until asperities of mating surfaces touch 

Hydrostatic lubrication 

(1) A form of thick film lubrication, but instead of being self- generated, it is supplied from an  external source by oil under pressure from a pump. 
(2) Lubrication for Crosshead Bearings, with attached pump. 

Elasto-hydrodynamic lubrication

(1) Applies to line contact or nominal point between rolling or sliding surfaces, such as rolling  contact bearings and meshing gear teeth. 
(2) Thin film or squeeze film lubrication limits metal to metal contact. 
(3) Elastic deformation of the metals occurs, and there is effect of high pressure on the lubricant.

Action to be taken if lub oil sump level of M/E decrease

Check rate of decreasing if slowly decrease, fill up L.O and find the leakage without stopping  engine
If rapidly decrease, inform to bridge and stop the engine. Find the leakage and repair.

Possible leakage points: 
     Bed plate crack (check engine room bilge) 
     Piston cooling L.O system (check scavenge space & under piston space {entablature}) 
     L.O cooler & L.O purifier 
     All pipes and connection 
Check L.O return valve from crankcase to sump tank close or not 
Check oil scraper rings & stuffing box

Actions to be taken if M/E temp: goes high during operation

(01) Inform bridge & reduce engine speed
(02) Check engine overload or not (Exhaust temp:, fuel rack,..) 
(03) Check L.O sump & L.O cooler & L.O purifier temperature (set value)
(04) Check L.O sump tank heating valve. 
(05) Shut L.O cooler by-pass totally after stopping (or) too high temperature not fall 
(06) Clean L.O cooler 
(07) Check sump tank heating coil leakage 
(08) Make L.O onboard test (esp Viscosity) 
(09) Check L.O piping system leakage or blockage 
 (10) Make (inspection & check bearing clearance & loosing attachment 
 (11) Check ampere (or) load when turn the turning gear

Factors effecting the establishment of hydrodynamic lubrication

Viscosity of oil 
Load acting on the bearing
Surface smoothness of moving parts
Speed of rotating 
Continuous LO supply 
Bearing clearance, bearing length and pin diameter. 
There must be convergence between fixed end and moving surface.

TAN and TBN

It is the neutralization value of used engine lube oil. 
The ability of an oil to react with a base reagent which indicates the acidity expressed as TAN. 
The ability of an oil to react with acidic reagent which indicate the alkalinity expressed as TBN.
The results are expressed intern of milligrams of potassium hydroxide (KOH) required to
neutralise one gram of sample oil for both TAN and TBN. 
 TBN for an oil used for 
 
Crosshead type diesel engine crankcase is 8mg KOH/gram of oil. 
For trunk type engine using heavy oil is 30mg KOH/gram of oil.

Sunday, April 12, 2020

Procedure for adjusting and checking the timing of M/E fuel injection pump

Jerk type fuel pump::

With a jerk type fuel pump , the fuel pressure starts to rise when the tip edge of the plunger cutt off the spill ports as the plunger ismoving upward on the delivery stroke. To check the accurancy of the start of injection , the engine crank angle for the start of injection must correspond to the manufacturer setting when the plunger is at this point

Method I ::
On some pump it is possible after isolating the fuel and draining the pump , to remove erosion plug and sight through the spill port while turning the engine. At the point where the edge of the plunger is seen to cover the top of thr spill port , the crank angle for that particular unit is noted and compared with the manufacturer recommendation.

Method II::
On some pumps i may be necessary to remove the top cover of the pump and delivery valve and measure the distance from thr top of the barrel to the top of the plubger.The manufacturer will give the correct distance at which the plunger has covered the spill ports


Adjusting ::
Timing can be adjusted by altering the position of fuel cam on the camshaft . This is done by hydraullically expanding the cam on the cam shaft . 
On some other pumps , small adjustment can be made by adjusting relative height of the plunger and barrel by placing the shims under thr foot of the plunger or under the fuel pump body in which the plunger is located.
On pumps fitted with VIT start of injection can be adjusted using ViT rack for individual pumps

Why 3 fuel injectors are used instead of single injectors

  • Modern crosshead engine fitted with a centrally mounter exhaust valve utilize uniflow scavenging
  • Because of this , 3 injectors are placed circumferentially around the cylinder head.
  • The atmosing holes , which are of different design to those of centrally placed injectors are designed to inject the fuel into the air swirl without contacting the liner surface.
  • A single injector could not be used because because it would result in poor air/fuel mixing with poor combustion and localized high temperature, although some ebgine utilizes 2 injectors per cylinder.
  • Due to tangential design of the scavenge ports ,chatge air rotates around the cylinder acts in swirl action which promotes better mixing of fuel from 3 injectors and the air.
  • This overall result in uniform temp distribution , more efficient combustion and lower exhaust temperature

Friday, April 10, 2020

Scavenge efficiency

The scavenge efficiency (Se) is the ratio of the trapped fresh air to the total mass trapped in the cylinder.
Others define scavenge efficiency as the ratio of trapped fresh air to the maximum theoretical amount of fresh air that could be retained in the cylinder

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Thursday, April 9, 2020

Ammendments to Fuel standars ISO 8217-2017compared to previous edition

Changes with respect to ISO 8217:2012
This sixth edition reflects important and significant changes. These include substantial amendments to the scope (Clause 1) and to the general requirements (Clause 5).

Changes to the distillate fuels include the following:
— additional grades, DFA, DFZ and DFB have been added with a maximum fatty acid methyl ester(s) (FAME) content of 7,0 volume %;
— the sulfur content of DMA and DMZ has been reduced to a maximum of 1,00 mass %;
— the sulfur content of DMB has been reduced to a maximum of 1,50 mass %;
— requirements for the following characteristics have been added to winter grades of DMA and DMZ: cloud point and cold filter plugging point.

The following annexes, previously included, have been deleted, but the key information is included in the body of this document or is available in referenced industry publications:
— Sulfur content;
— Flash point;
— Catalyst fines;
— Precision and interpretation of test results.

Checking of 15 ppm meter

15 ppm meter is checked by putting a soft plastic bruss inside the sampling box from the top that deflect the passing optical wave and ppm intensity vary and hence checked.
But calibration part is done by shore team and afterward calibration report is made by him..

Main engine stuffing box leak how to know from outside

Stuffing box leakage can be found out from outside.
One drain pipe from stuffing box connected yostuffing box drain through funnel.
If air is coming out-sealing rings are leaking
If drop by drop oil coming- stuffing box working good.
If too much oil coming-scrapper ring leaking or drain from crankcase is choked

Material of connecting rod bolt ,importance of elongation, nature of stresses in this component and why should these bolts be replaced after some time in service

The connecting rod bolt in service is subjected to: 
a. A dynamic tension loading due to centrifugal force of the mass of connecting rod 
rotating with the crank pin 
b. A dynamic tension loading owing to inertial forces of the reciprocating mass of the 
piston which is fluctuating with angular displacement of the crank and having the 
peak value at an instant of 360˚ after the firing TDC in a cycle of operation 
c. A dynamic shear stress at the parting of the two halves of the bearing housing 
Dowel pins with fitted bolts or serrations at the face or both are used to reduce shear loading  on bolts and possibility of fretting. 
Bolts should be constructed of materials having high resilience and should not be stiffer w.r.t  bearing housing. 

Pretension of the bolts should be regarded as the single most important factor which 
contributes towards the fatigue life of the material of the bolt. Pretension must be kept high 
enough, so that the increase in stress owing to dynamic loading remains within the range of 
stress already given by pretension. 

Some routine checks on this part are (rejection criteria of the bolt) 
a. Check for corrosion by acidic lube oil, discard if any present on shanks 
b. Check the length of the bolt against a new or bolt tolerances. If longer, yielding of 
the material should have taken place. Renew the bolt in this circumstance 
c. Check for mechanical damage, especially on shanks 
d. Check for fractures by NDT 
e. Check the landing faces for uneven tightening 
f. Discard the bolt when either designated life, over speed failure or piston seizure has 
occurred

Difference between an over speed governor and a constant speed governor?

If within a governor, an over speed detection/actuation mechanism is provided to trip the 
engine in case of over speeding and or rapid increase of speed then the governor is called an  over speed governor. These were the obsolete governors and commonly had fly or bob 
weights restrained by spring. When the engine exceeds a predetermined speed, the weight 
moves out to strike some form of fuel cutoff. 
Governors designed to maintain the engine speed at the set point are called constant speed 
governors. These are also referred to as isochronous governors like the ones usually installed  on COPT and main engine

P-Alkalinity and T-Alkalinity

P-Alkalinity:
Phenolphthalein is less alkaline than hydroxides or carbonates, and when it is 
added to a sample containing hydroxides and or carbonates it will first neutralize the 
hydroxides forming salts, it will turn pink in color. The acid used after this coloration will first  neutralize the hydroxides forming salts, it will then react with the carbonate molecules 
present forming bicarbonate molecules. Bicarbonate molecules are less alkaline than 
phenolphthalein, hence, the pink coloration disappears once all the hydroxides and 
carbonates have been dealt with by the acid. One bicarbonate molecule is formed from two 
carbonate molecules, hence in the test the quantity of acid used is a measure of the 
alkalinity due to the hydroxides (caustic) present and half the carbonates. 

T-Alkalinity:
Methyl-orange indicator is less alkaline than phenolphthalein and bicarbonates. 
It can be used initially in place of phenolphthalein or in continuation after the alkalinity to 
phenolphthalein test. If no yellow coloration results when the methyl-orange is added to the 
alkalinity to phenolphthalein sample no bicarbonates are present. Hence no carbonates are 
present. Therefore, the alkalinity as determined in the alkalinity to phenolphthalein test has 
been due to hydroxides alone.

Procedure of plugging boiler of boiler tubes

Procedure of plugging water tubes 
a. Clean the face of leaky tube remove all the scales and dirt both in steam and water 
drum 
b. Plug with steel plug, hammer tight and weld 
c. Cover this tube on the furnace side with heat resisting material

Procedure of plugging smoke tubes 
a. Steel plug with stud and tightened by nut at both the ends

What are the reasons for a lot of deposits in the scavenge space of a marine engine?

The usual reasons for a lot deposits in the scavenge space of a marine engine are 
a. Chocking of the scavenge drains 
b. Blow-by due to broken or sticking piston rings
c. Excessive liner wear 
d. Faulty injection due to altered timing, bad fuel or incorrect atomization 
e. Blow back of exhaust due to increased exhaust back pressure 
f. Leaking piston stuffing box 
g. Excessive cylinder liner lubrication

Microbial infestation of lub oil

Microbial infestation of lube oil is the undesirable growth of bacteria, yeasts and/or moulds in  the oil. 
Infestation of the oil can be due to contaminated seawater, hydrocarbon source already 
onboard or due to poor housekeeping practices. 
The problems are like tank washing with contaminated seawater, water ingress from leaks of  seals (as in a stern tube, CPP etc.,), leaking cooling water, microbe infested fuel oil 
contamination, onboard contamination due badly maintained or stagnant tanks (long lay off),  bilge water etc., 

The effects of such microbial infestation can be
a. Slimy appearance of the oil; the slime tends to cling to the crankcase doors 
b. Rust films 
c. Honey-colored films on the journals, later associated with corrosion pitting 
d. Black stains on white metal bearings, pins and journals 
e. Brown or grey/black deposits on metallic parts 
f. Corrosion of the purifier bowl and newly machined surface 
g. Sludge accumulation in crankcase and excessive sludge at the purifier discharge 
h. Paint stripping in the crankcase 
i. Additive depletion 
j. Rancid or sulfitic smells 
k. Increase in oil acidity or sudden loss of alkalinity. (BN) 
l. Stable water content in the oil, which is not resolved by the purifier 
m. Filter plugging in heavy weather 
n. Persistent demulsification problems 
o. Reduction of heat transfer in coolers
 
To counter the problems of the microbial infestation, it is necessary to take steps to prevent 
such infestation. 
The microbial infestation is not possible without the presence of water. Some water in the oil  in inevitable due to leaks, condensation, etc., so it is necessary to constantly purify the oil. 
Tanks should be provided with drain cocks at the bottom most part to regularly drain the 
tank of water. The tanks should be designed to prevent any pockets where the flow is 
minimal or stagnant. The oil should be stored outside the 15~35˚C range. This temperature 
zone is very conducive for bacterial growth. Preferably, the tank should be kept at a higher 
temperature to facilitate sterilization. Lube oils have a maximum risk of infestation in the 
water-cooled pistons engine. Therefore, care must be taken not to allow any scope for water  leakage from the cooling system and the coolers should be kept leak free. 
Once the oil is infested, it is necessary to kill the bacteria by physical, chemical or other 
means. 

PHYSICAL MEANS: 
a. Settling: microbes settle the as they have a higher specific gravity (Sp.gr. 1.05) 
b. Centrifuges: they can be separated by centrifuging 
c. Filtration: microbes can be filtered by suitably staging filters 
d. Heat: This is a function of both temperature and time at that temperature. A 
temperature of over 70'C for 20 minutes is effective in killing the microbes. However 
this is difficult to achieve at the plate surfaces and it may be necessary to sterilize the 
tank first say by the use of steam lances before filling with oil for heat treatment 

CHEMICAL MEANS: 
Killing microbes using microbes is easy and effective, however the selection of chemicals 
appropriate for the system application and should be done with care. Such things as 
compatibility and hazards should be taken into account. However, if the infestation is acute,
 higher concentration of dosage of the chemical is required. This may render the oil unusable and has to be discharged to shore facilities. 

Other means of combating the microbes are available like 
a. Irradiation (UV Rays, Gamma Rays or X Rays)
b. By ultrasonic treatment of the infested oil
c. Using microwaves
d. Continuous pasteurization of the infested oil and heat control

Bore relief in a bearing

The bearing sliding surface is machined at the mating faces of the upper and the lower shells  to create bore reliefs. Their main objective is to compensate for the misalignments, which  could result in a protruding edge (step) of the lower shell’s mating face to that of the upper  shell. Such a protruding edge can act as an oil scraper and cause oil starvation

What is the difference between coagulation and coalescing?

A Coalescer filter element consists of some pre-filter for particulate removal followed by 
compressed inorganic fiber coalescing unit in which water is collected into larger globules 
Coalescing action is relatively complex and simply it can be said to be due to the molecular 
attraction between the water droplets and the inorganic fibers is greater than that between 
the oil and the fibers. When the water globules are large, enough they will move with the
stream out of the coalescing unit. 
Coagulation is the process of agglomeration of smaller particles into larger particle due to
intermolecular attraction between similar molecules in preference

Why copper gaskets are 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 considerable 
mechanical stress, resulting from elastic strains internally balanced. These elastic strains are  due to jamming of dislocations, which occurred during cold deformation (during service).
If  this cold worked gasket is heated to a sufficiently high temperature the total energy available  to the distorted regions will make possible the movement of atoms into positions of  equilibrium so that the elastic strains diminish and the locked-up energy associated with  them ‘escapes’. Tensile strength and hardness will fall to approximately their original values  and capacity for cold work will have returned.

Wednesday, April 8, 2020

Generator lube oil sump level increases, what are the checks you would carry out?

a. Check that the generator lube oil systems valves are correctly positioned and that the 
sump filling valve is holding 
b. Ask the personnel for if they have carried out any transfers just before, related to the 
sump oil of the generator 
c. Check the purifier for correct operation and that no water is being discharged with the 
purified oil 
d. Change over the generator concerned, isolate it and check the sump for any 
contamination like water. Basing on the findings further inspections can be carried 
out, like checking the cylinder liner jacket cooling water sealing O-ring etc.,

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 pressure 
b. 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 also 
termed as “bigger range” 
b. Checking the liquid level of the outer pipe (close the vent cock, open the upper gauge 
cock 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” the 
respective readings (as in ‘a’ and ‘b’) should match numerically 

MAINTENANCE & INSPECTION IN DRYDOCK: 
Disconnect and remove top cover with attached internal stand pipe. Disconnect and remove 
Flame 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 supplied  tar epoxy by hand brushing to all internal surfaces. Level gauges, cocks and protective  housing to be removed and transported to workshop for cleaning and overhaul. Dismantle  sight glass tubes and cocks for overhauling and cleaning. Upon completion, re-assemble and  re-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 and 
0.07kg/cm2 in the presence of the attending superintendent. Record and submit calibration 
of valve settings. Close on completion with new shipyard supplied approved type jointings 
and sealing compound and bolts and nuts.

What is a PV breaker? Why is it fitted?

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

Pressure-Vacuum breaker is fitted to the IG main line on the deck to protect cargo tanks 
from the following: 
a. Abnormal rise of pressure in the cargo tanks which occurs when cargo is loaded with 
specified rate and that all gas outlets are closed 
b. Abnormal drop of pressure in cargo tanks which occurs when cargo is unloaded with 
the 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 breather 
valves fails to operate properly for the fluctuation of the pressure in cargo tanks, due 
to variation in atmospheric and sea water temperatures, altering the vapor pressure 
inside tanks

What is the routine anchor windlass maintenance?

a. Brake drum should be free of oil, grease and other deposits. The brake drum should 
be cleaned periodically with a solvent prescribed by the maker 
b. The brake drum and the disk should be checked for wearing out or damage 
c. Gear oil should be checked for contaminants and level 
d. The direction of tensioning should correspond to the correct operation of the brake. As 
the reverse direction for tensioning would render the brake ineffective, check should 
be carried out to ensure the same 
e. Brake test of the windlass is to be carried out to the pressure mentioned by the 
maker on the jack tool. If necessary, the spring tension adjusted. It should be done in
guidance of the instructions and in the tensioning direction. The number of turns on
the drum should also be checked and should be same as to the makers quote 
f. The securing device of the tension spring adjust should be checked periodically for 
any tamper
g. Anchor windlass testing should be carried out to check the efficiency of the windlass. 
The windlass should raise the anchor with chain from 82.5m to 27.5m at a mean 
speed of 9m/min 
h. The foundation of the windlass should be checked 
i. Other routines of the prime mover should also be carried out like for the windlass 
electric motor or the hydraulic motor as the case may be

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 hardness 
salts, which may enter. These salts would deposit as a scale on the heating surface if reserve  were too low while, too high a reserve leads to foaming and possible excess production of  sludge. It also gives alkalinity.
At high pressure and temperature, reaction from left to right will be more. Therefore, it is
very important in high pressure boilers to keep the reserve level up to required concentration
to avoid excessive caustic alkalinity and thus caustic cracking.

In high pressure boilers where there is a risk of caustic concentration and subsequent caustic  Attack it is common to apply a coordinated or congruent phosphate control programme.
These control methods are based on the hydrolysis of tri-sodium phosphate (TSP) and
disodium Phosphate (DSP) in the boiler water.

The objective is to maintain a desirable pH without the presence of free OH alkalinity. The
desired conditions are obtained by maintaining the relationship of the pH to phosphate
concentration in the boiler water at less than that of the equivalent stochiometric solution of
Na3PO4 (<3:1). This is achieved by the equilibrium reaction above. The congruent phosphate
approach utilizes mixtures of TSP and DSP to further ensure the absence of free OH alkalinity
and usually run with a Na:PO4 ratio of <2.8.

What is caustic cracking or embrittlement? What is its cause? Suggest remedy This is

This is a form of intercrystalline/intergrannular cracking and occurs when a specific corrodent  and sufficient tensile stress exists. Iron consists of ferritic granules bonded by iron carbide so  this gives a scope of the intergrannular corrosion. This can be found in water tubes, super  heater, reheat tubes, and in stressed components of the water drum. The stress may be due  to thermal, bending or residual stress (due to welding). This usually occurs as a localized  attack in the combination of NaOH, some soluble silica and a tensile stress. The mechanism  begins with the accumulation of the corrodent NaOH due to – 
a. DNB (departure from nucleate boiling) 
b. Deposition 
c. Evaporation at the water line 
d. Small leakage 
e. High heat flux (rapid evaporation) 
f. High pressure

This corrosion below 149˚C or with NaOH concentration below 5% is rare. Increased 
susceptibility occurs at about 20~40%. This corrosion is difficult to identify in the beginning 
and ND testing has to be carried out at the suspected areas. At some time after the initial 
start of the corrosion, this manifests as a whitish highly alkaline deposits or sparkling 
magnetite. 

COUNTER MEASURES: 
a. Applying heat treatment process to relieve stresses after fabrication/repairs (welding 
etc) 
b. Correct and accurate boiler water treatment 
c. Avoid DNB 
d. Avoid accumulation of the deposits 
e. Prevent leakage of corrodents 
f. Prevent carryover 
g. Use of rifling in the water tubes

Explain the various rudder inspections and testing in the dry dock

a. Visual examination of the rudder plating for cracks and distortion 
b. 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 breached 
rudder and the breach to be located by air pressure testing and applying soap 
solution, 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 checked 
e. Check the rudder stock for corrosion, erosion and any damage 
f. 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 water 
h. After draining and re oiling the internals, plug the drain and check the effectiveness 
by a vacuum check and cement the plug 
i. The rudder stock gland packing has to be checked and renewed

What is the course of action after finding that a bottom end bolt is slackened?

a. Check the length of the bolt 
b. Check whether it is within the limits 
c. Check for cracks / surface finish. Check the threads 
d. 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 along 
the twisted plane 
e. If found alright, tighten the bolt and check the remaining bolts

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 rod 
from 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 vibration 
amplitude, thereby preventing its fracture due to vibrations. These can be arranged as a 
group of three screws positioned equilaterally at the antinodal point. Each screw consists of a  stud, which is hand tightened by screwing the outer sleeve and held in place by a lock nut 
which is tightened to a torque specified by the manufacturer.

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Explain the purpose of the hunting gear

a. To put the pump on stroke gradually 
b. To stop the pump at the end of the stroke gradually 
c. To lock the rudder at desired position till further movement is given at helm 
d. To transmit movement of telemotor to pump 
e. Spring in the hunting gear store extra control movement to ensure that the pump 
operates at the maximum capacity for major part of the turning operation

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 bronze 
Copper: 58%, Iron: 1%, Aluminium: 1%, Manganese: 1%, Nickel: 0.5%, Zinc: 
38%, Tin: 0.5%

What is the material of the ship side valve?

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

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 hole 
is lesser in size than the corresponding circular hole. More over it is prime concern to have a  smoothed generous radius at the corners to eliminate stress concentration. Hence other 
geometrical 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 be 
provided around the opening. The thickness of the ring depends on the axis length along the  dirrection in which the stresses are maximum and the thickness of the shell. It is important to  align the minor axis along the length of the vessel, as the stress in this direction is  maximum.

Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= 
thickness of the shell plating 

Circumferential stress: Pd/4t 
More over a considerable material and weight saving is achieved as minor is along the 
direction of maximum stress.

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 thrust 
housing. This is achieved by forming white metal rings on the sides of one main bearing shell 
that allows the shaft to run with a small clearance between running faces on the two 
adjacent webs. 
In some engines a small collar may be provided at one side of the bearing. It is important to 
appreciate that only one such locating bearing should be fitted to any one shaft, otherwise 
the differential thermal expansions of frame and the crankshaft may cause problems.

What are the problems in cast iron welding?

a. Brittleness (cracks easily) 
b. High carbon content in the form of graphite 
c. Close grain structure 
d. Poor thermal conductivity and differential cooling 
e. Possibility of stresses and distortion

What are the advantages of a thin shell bearing?

a. Increased fatigue resistant properties 
b. High load carrying capacities 
c. Embed ability 
d. Conformability 
e. Bedding not required 
f. Easy storage, easy fitting, light in weight 
g. Increased (enhanced) mechanical properties 
h. Better heat transfer due to reduced thickness and uniformity of the contact with the 
bearing housing

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 the 
refrigerant and the oil is difficult 
b. To condition the lube oil, by maintaining the viscosity so that the lubrication is 
effectively carried out. 
c. This prevents the lube oil achieving its floc point which may cause narrowing or 
chocking of the passages (flocculation)

Why a crankcase relief door is not fitted in the refrigeration compressor crankcase?

a. Possibility of the contamination of the refrigeration system by air by leaks 
b. Oxygen is not available in the compressor crankcase 
c. The incoming refrigerant temperature is low and chances of hot spots is low 
d. Crankcase forms the suction chamber of the compressor and chances exist that the 
compressor may draw in air and moisture

What is a second order moment?

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

What is 1st order moment?

These moments acts in both vertical and horizontal directions. For engines with 5 cylinders 
or more, the 1st order moments are of rare significance to the ship but it could be of a idisturbing magnitude in the 4 cylinder engines. Resonance with a 1st order moment may 
occur for hull vibrations with two and/or three nodes. 1st order compensator can be 
introduced in the chain tightener wheel. It comprises of two counter rotating masses 
rotating at the same speed as the crankshaft.

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

a. Poor combustion due to faulty injection system 
b. Low compression 
c. Insufficient scavenging air 
d. Fouled exhaust system 
e. Broken piston rings 
f. Ineffective lube oil seal 
g. After burning, bad fuel and other fuel assisted faults 
h. Faulty cylinder lubrication 
i. 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 combustion 
chamber, low fuel injection pressure etc., each compounding the cause for black 
smoke

What are the causes of cylinder head cracking?

a. Scale deposits 
b. Inefficient cooling water 
c. Uneven tightening of bolts and fuel valves 
d. Fluctuating cooling water temperature (excessive temperature gradient) 
e. Overloading or racing of engine 
f. Faulty relief valve 
g. Mechanical failure due to gas corrosion, acidic corrosion due to leaky exhaust valves 
h. Water side corrosion

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

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

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 the 
camshaft speed, then the spring may vibrate axially and are said to surge. Surge can be 
avoided by modifying the sizes of springs by arranging the springs in pairs and fitting one 
inside 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 a 
concentric springs arrangement. The net stiffness is equal to the sum of individual stiffness.

Tuesday, April 7, 2020

Engine not reversing or starting in only one direction. Reasons

  • Start air valve for that unit may be sticking . The remedy is to give a kick in the opposite direction . Now a different unit will recieve start air due to the change in the crank position
  • The reverse control valve is jammed.
  • The reversing servo motor of the fuel or start air distributer is jammed or gets stuck befor reaching a new end position due to insufficient oil pressure . Therefore the enfine turns on air but no fuel is released as the rotation direction safegaurd block it
  • If the engine is running in one direction and reversed , propellor continues to turn in that direction. Therfore more air and fuel is required for starting against the propelllor force . If the engine still doesnt start , the propellor may tend to turn the engine in the orginal direction ie opposite to the given movement . Therefore the rotational direction safegaurd blocks the fuel
  • Reversing interlock malfunctioning
  • The coil of the solinoid valve for thr desired direction or rotation doesnot get voltage
  • Control air signal for desired direction of rotation doesnot reach the engine . Loosen piping and check the air route or the defective valve.
  • Proximity sensor faulty ( of air distributer or fuek pump servo motor)

Engine fail to start on air. Reasons

  • Low air bottle pressure or air line valves may be shut
  • Air bottle isolating valve or automatic valve or distributor malfunction
  • Control air valves faulty or less control air pressure 
  • Start air valve jammed.
  • Turning gear engaged or limit switch faulty.
  • Bursting diaphram on start air line damaged.
  • Fuel lever on manoeuvring stand not on remote mode.
  • Not sufficient spring air pressure to shut the exhaust valve , there by causing loss of compression.
  • Auxiliary blower not running or not on auto mode.
  • No oil pressurr due to the exhaust valve being open or insufficient spring air pressure
  • Start air distributer has not activated itz end stop valve
  • Start air distributer piston is sticking.
  • Start air distributer is wrongly adjusted
  • Start air distributer control valve is sticking
  • Cylinder air start valbe are defective or sticky
  • Othet interlock - Aux blower , LO low pressure, CW low pressure

Dezincification

  • Dezincification of brass is a particular type of corrosion occurs in th presence of sea water.
  • The attack remives zibc from the alloy , leaving porous copper which is soft.  The problem is marked by a patch of copper color on the brass.
  • Dezincification is inhibited in brass which are intended for sea water contact, by additives of a very small amount of arsenic or other element.

Brinelling

It is the phenomenon observed in ball and roller bearing which leads to premature failure of bearings

There are two types of bearings

True brinelling

It happens due to faulty assembly of bearing , that is while fitting excessive hammering is carried out which deformates the ball and raw

False brinelling

It is due to vibration caused by machinery itself or by vibration transmitted by other machinery thus brinell may occur during machine standstill or in operation

To avoid brinelling

  • Reduce vibration 
  • Top bearing of purifier is mounted on spring casing
  • Machine not to be kept in standstill for long term at regular intervals
  • After overhauling and trying out purifier it is advisablento remive bowl and keep outside to avoid damage to bearing.
  • Avoid excessive hammering while fitting

Stresses in crankshaft

  • Bending stress- combustion load , inertia force , static weight
  • Axial bending- propellor axial thrist
  • Torsional stress - transmission of variable torque
  • Shear stress
  • Rapid compressive stress- shrinkage of journals on webs
  • High tensile hoop stress

Tie rod persistently becoming slack . Reasons

  • Uneven tightening procedure
  • Uneven tightening torque
  • Over tightening
  • Overloading of main engine
  • Threads - not machined properly or cleaned
  • VIT not adjusted -Pmax too high
  • Improper power balance
  • Rough weather- fluctuation
  • Scavenge fire
  • Loose foundation bolts
  • Loose pinching screw
  • Engine is new - no proper matching and bedding is done
  • External vibration - Hull fouling , propellor tip clearance is less

Identifying slack tie rod

  • Check tensioning
  • Adjacent cylinder head seen lifting.
  • Pressing thumb in contact with cylinder jacket and nail in contact with tie bolt nut - small movement
  • Fretting wear
  • Visually - the cylinder head at adjacent of the slacknor broken tie rod can be seen lifting up during end of compression stroke or at firing stroke
  • By dial gauge - Put dial gauge between cylinder head bolt and tie rod nut. See the deflection in the gauge.
  • Washer -If washer fitted between the tir rod bolt and nut , then it can be seen twisted during the firing stroke or at the end of compression stroke

Co-oefficient of performance ( COP)

  • It is the ratio of the useful output of the cycle to the work input .
  • In cooling cycles this becomes the ratio of refrigeration effect to the heat of compression

COP=Refrigeration effect/heat of compression

A/E unable to take load and hunting too much . Reasons

  • Governer malfunctioning
  • Governer oil dirty
  • Droop setting not proper
  • Sticky linkages
  • Water in fuel and air lock in fuel line
  • Fuel oil filter chocked and fuel quality poor
  • Viscosity not maintained.
  • Scavenge air pressure low- fouling of T/C , suction filter dirty , air cooler chocked
  • Improper tappet clearance
  • Overdue for decarb
  • Slippage of cam and cam shaft- thus alteration in fuel pump timing, inlet and exhaust valve timing
  • Fuel pump overhauling due

Checks after decarb -Main engine

  • Open JCW inlet and outlet, purge the unit , check for leak.
  • Check pump pressure
  • Expansion tank needs to.top up
  • Confirm nothing left inside crankcase
  • Open spring air , control air , check for leak
  • Start LO pump , check LO flow and check for any leak
  • Inspect crankcase for any rags or tool
  • Confirm bolts are secured with locking wire.
  • Turn engine few revolutions and check amperage
  • Open fuel inlet valve , check for recirculation and leak
  • Check for cylinder lubrication  ( press prelube on HMI in case of Alpha lubrication  or manual cranking )
  • Open indicator cock , check starting air valve for any leak.
  • Increase cylinder lubrication for that unit.
  • Carry out long blowthrough.
  • Try out main engine on ahead and astern direction
  • Check exhaust valve operation
  • Check exhaust gas temp and leakage.
  • Check piston cooling oil temp
  • Check scav temp:

Checks after decarb before starting Aux engine

  • Confirm all fitting has been closed properly
  • Adjust tappet clearance. Take crankshaft deflection if bearings renewed.
  • Open cooling water check for leak (through cylinder head , crankcase)
  • Purge the cooling water line ,check pressure. Open warming up line
  • Start LO priming pump , check flow , check pressure , purge LO cooler and filter
  • Check play of connecting rod and measure clearances
  • Engage turning gear and turn few revolution
  • All ok , carryput blow through
  • Check pressure of bearings
  • Check temp of all bearings
  • Start engine at reduced speed.
  • Check all parameter ( LO pressure , FO pressure, scav pressure , CW pressure, exhaust temp)
  • Check for any leakage
  • Stop engine and carry out crank case inspection
  • Adjust tappet if required
  • If all OK run engine in Off load condition and check parameters
  • Run engine on partial load and slowly increase load.

Monday, April 6, 2020

How to change rudder carrier bearing

  • Lock steering gear in mid position
  • Remove the earth wire
  • Measure clearances ( rudder drop and jumping clearances )
  • Fix eye bolt to rudder stock and take load with the help of chain block at strong point provided
  • Remove the bolts of gand housing and remove gland packing.
  • Remove the locking ring
  • Remove grease plug
  • Remove the moving cone which is in 2 pieces( boted with each other). Put eye bolt diametrically opposite.
  • Remove the bottom half which is also in 2 pieces and attached to ahip structure via chocks
  • **Note - The bearing is conical shaped to locate the rudder stock . The bearing top and bottom half is on 2 halves
  • Material - Cast iron (CI has self lubricating property and greater shock absorber)

Advantages of CROS piston

  • Multibored cooled piston
  • High top land
  • Improved combustion
  • Approx. 100 degree lower temp on top ie, reduction in piston temp
  • Avoid impingement on piston
  • Less carbon deposition
  • Injector gets more space for penetration
  • TBO increases

Purpose of orifice in scavenge drain tank vent

  • To prevent loss of air.
  • To restrict the moisture drain flow , so that in case of excessive condensation pre warning alarm shlould intiate
  • If no orifice , then there is a loss of pressure along with scavenge drain , sludge will come to deck and make it dirty and lead to pollution
  • The orifice of size about 10 mm is fitted in the vent , to release the pressure in controlled way so that there will be a continuity of drain maintain to scavenge drain tank and scavenge pressure also maintained

Boiler emergency operation

  • Make sure FO circulating pump is running, or else start pp
  • Take sufficient water in boiler , ensure from gauge glass.
  • Change over boiler control from auto to emergency mode.
  • Start FD fan and open damper to max position . Run sufficient time ie, 3 minute ( pre purge) .After purging adjust the damper to minimum.
  • Start pilot burner DO pump.
  • Put ignition switch ON , spark will generate.
  • Manually operate the solinoid valve to open DO to pilot burner
  • Once pilot burner ignited , manually operate solinoid valve to open FO toain burner.
  • After 10 second of main burner fired , put off ignitor and pilot burner.
  • Adjust air fuel ratio manually by observing smoke
  • Keep close watch on boiler
  • Once boiler pressure reached to required pressure close the solenoid valve for main burner manually.
  • Keep damper to max position for 1 minute
  • Stop FD fan

Chattering and Simmering

Chattering

Rapid opening and closing of the valve is known as Chattering

Causes:

  • Insufficient blow down
  • More back pressure due to under size discharge piping
  • Insufficient steam flow to the valve
  • Lifting with water

Simmering

The valve is just about to open and has indifinite contact. An audible sound or visible escape of fluid between seat and disc at an inlet static pressure below the popping pressure and at no measurable capacity.
It is the pressure zone between the valve set pressure and the popping pressure . In this pressure zone the valve is only slightly open and therefore discharging a small percentage of its rated capacity.
Simmering can damage a valve because it will leak some fluid that can accumulate in the valve and start corroding it. If a safety valve simmers a lot , consider increasing the valve set point , or if simmering below setpoint , it may need to get repaired.
 

Purifier not reaching full rpm .Reasons

  • Improper touching of friction clutch
  • Touching with brake
  • Excessive sludge in bowl
  • Bearing failure
  • Motor running at overload
  • One phase power failure
  • Sump oil level too high
  • Vertical shaft and horizontal shaft out of alignment
  • Improper bowl assembly

Tribology

Tribology is the science and engineering of interacting surface in relative motion.. it includes the study and application of the principles of friction lubrication and wear
Tribology is the branch of mechanical engineering and material science

Equalising line on TEV

  • It is used in large evaporators , where pressure drop take place  at the end of evaporator ie, more than 0.3 bar
  • The pressure acting outsode the bellow from heat sensing bulb and capillary tube is total of the saturation pressure plus superheat . This pressure is trying to open the valve , overcoming the spring pressure.
  • The equilizing line has saturation pressure at the end of an evaporator coil acting from the bottom of the bellow ( diaphram ) . Hence the saturation pressure from equalizing line and capilliary tube is balancing each other.
  • The additional pressure from outside of bellow due to superheat is now reaponsible to open the expansion valve. By this arrangement , we are getting actual degree of superheat . Correct degree of superheat ensure that refrigerant is used efficiently and no liquid reaches to compressor  suction . Also evaporator shoulf not starved of  refrigerant.

How to remove broken stud ?

  • Clean the surface before trying to remove the broken stud.
  • Flatten the broken end.
  • Punch with centering punch at the centre of broken stud.
  • Use a small drill to make a hole on the broken stud , ensure no damage to threads.
  • Again drill a little bigger hole and ensure no damage to threads
  • Use the stud extractor to remove the broken stud by rotating in anti clockwise direction
  • Note-- stud extractor has a left handed thread. We can also remive the broken stud by using WD 40 and turning the stud with the help of screw driver or chiesel

what is SAE 20W40

  • SAE- Society of automotive engineers
  • 20   -at cold temperature it will act as SAE 20 & when heated to 100degree it will behave  like SAE 40
  • W - winter grade
  • 40 - grade at 100 degree

Sunday, April 5, 2020

Alcap system important feature

It can purify high density residual fuel.

 It reduces the loss of oil during desludge operation.

It acts in dual mode (either clarifier mode or purifier mode).

It adjusts automatically according to the nature of oil.

It’s fully automatic. It operates in auto mode.

It has flexible and easy installation design.

It has eliminated gravity disc and introduced flow control disc.

Procedure for cutting off cylinder unit

The following sequence would be carried out for ships which use the MAN B&W slow speed engine:

Stop engine, isolate systems and allow to cool

Ensure a procedure is written that minimises the risk to personnel during the operation.

Discuss the task and written procedure with the engine room personnel to ensure they are familiar with the risks, and the methods to be used to minimise these risks.

Ensure the fuel pump is de-activated by lifting roller and locking.

Lift exhaust valve actuators so exhaust valve remains closed during running. (Note: the air spring supply to be left open)

Dismantle air start supply line, and blank with suitable steel plates, the main and control air pipes

Dismantle bottom end bearing, and turn engine to suspend piston, crosshead and connecting rod from supplied crosshead supports.

Secure big end of connecting rod in crankcase.

Blank off main lube oil inlet to crosshead within the crankcase with a blanking plate.

Isolate the cylinder lubricator for that cylinder by placing all lubricators on no stroke.

Advantages and disadvantages of Rotary vane Steering gear

Advantages
  • Can be fitter without a rudder carrier
  • Steering gear applies a pure torque to the stock , eliminating any transverse Loading on the rudder bearings.
  • Compact hence are useful with twin rudder application
  • Saving in weight and intial cost
Disadvantages
  • Efficient seal is difficult ot achieve , this with small movements over much of the operating life can lead to problm
ie, 1.Mechanical advantage is low
     2.Has a leakage path from high to low pressure side. Usually limited to ships requiring low rudder torque
 

Advantage and Disadvantages of controllable pitch propeller

 Advantages of CPP

Improved Maneuverability.
Full ahead to astern un 12 seconds.
Lower ship speed can be obtained.
Crash stop feature.
Improved water flow into the rudder.
Full engine power available for astern movements.
Fewer engine starts.
Low thermal.load on engine.
Less engine wear.
Less stern tube bearing wear.
Lower starting air comsumption.
No requirement for reversing gear.
Higher engine efficiency
Pitch adjustable for hull fouling and different sea conditions
Engine power and speeds can be altered to stay clear of T/C surging zones


Disadvantages of CPP
Propellor heavier which will increase stress on tail shaft and stern tube bearings
Survey period reduced by 1 year
Additional cost during survey
Lower propellor efficiency due to large dia hub versus propeller diameter
Drop in efficiency range from 2 to 3 percent.
Increased risk of breakdown due to system dependence and greater chance of cavitation damage on propellor blades