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Class 2 and Class 4 Favourite MMD Oral Questions Asked By Every Surveyor in MEP and MOTOR Part-2
admin
#1 Posted : Saturday, June 1, 2019 11:05:07 AM(UTC)
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Turbocharger cutting-off procedures:

When it is necessary to cut-off T/C due to heavy vibration, bearing failure, etc. cutting procedure should be done as per engine maker’s instruction.
Cutting-off operation depends on number of T/C installed and number of T/C damaged.
Following procedures are in accordance with Sulzer RT engine practice:
Case I: Failure of one T/C, with Exhaust by-pass piping:
1. Lock rotor as per T/C manual.
2. Remove blank flange in by-pass exhaust piping.
3. Open covers of scavenge air trunk.
4. Auxiliary blowers must be running during operation.
5. If casing is cracked, stop T/C cooling.
6. If T/C is supplied with external lubrication, shut L.O. supply.
Output 25%: RPM 60% at MCR.

Case II: Failure of one T/C, of two T/C engine:
1. Lock rotor of damaged T/C.
2. Remove expansion joints of both exhaust inlet and air outlet of damaged T/C, and put blank flanges.
3. If casing is cracked, stop T/C cooling.
4. If T/C is supplied with external lubrication shut L.O. supply.
Output 50%: RPM 80% : Running T/C rpm must not exceed normal rpm:

Case III: Failure of all T/C of an engine, without Exhaust by-pass piping:
1. Lock rotors of all T/Cs.
2. Open all covers of scavenge air trunk.
3. Auxiliary blowers must be running during operation.
4. If casing is cracked, stop T/C cooling.
5. If T/C is supplied with external lubrication shut L.O. supply.
Output 15%: RPM 50%:

Turbocharger Washing:

1. In Slow Speed Large Output Engines, running on HFO, only Turbine Side Cleaning is necessary, owing to poor quality fuel (but some engines use Compressor cleaning.)
2. In Medium Speed Engines, running on Distillate Fuel, Turbine Side Cleaning is not essential but Compressor Side Cleaning must be done daily, under full steaming condition.
Purpose:
1. To ensure efficient running of TC.
2. To prevent Compressor and Turbine from deposits.
3. Carried out periodically at 250 ~ 1000 Running Hours, depending on running condition.

Blower side Washing:
1. Cleaning effects by mechanical breakaway of deposits, when small drops of water strike the surface.
2. ME at normal full load speed.
3. Fixed quantity of FW is injected into air stream by compressed air, before compressor.
4. Fixed quantity used depends upon blower size, to prevent water ingress into engine.
5. Open air cooler drain and scavenge drains.

Turbine side Washing:
1. Cleaning effects by mechanical breakaway of deposits, when small drops of water strike the surface.
2. Normally carried out when the sea is calm.
3. ME speed to be reduced, with permission from Bridge.
4. Reduce ME speed avoiding critical speed.
5. Exhaust gas temperature at turbine inlet < 300°C: TC speed ≈ 2000 rpm.
6. Warm FW is supplied slowly, and pressure depends on exhaust gas temperature and volume, not to vaporise all the water.
7. Open TC casing drain and can be stopped, when clean water comes out.
8. After washing TC kept running at same reduced speed for 3 ~ 5 minutes until all parts are dry.
9. Then increase ME rpm slowly, to normal rpm.

Cereal Grains or Activated Charcoal Particles Cleaning of Turbine: [Dry Cleaning]
1. Turbine side cleaning is superseded by Coconut Charcoal particles, with grain size
of 12 to 34 mesh.
2. No speed reduction required and cleaning can be done at full speed, once every 240 hours
3. Compressed air of (3 – 5 bars) is used to help the grains strike the deposited Turbine Blades and Nozzles, giving effective cleaning of hard particles.
4. Air supply pipe is fitted to solid grain container, and grains are injected into Exhaust System by air pressure, at the same point (as in Water washing) just after Exhaust Grids.
5. Turbine casing drain kept open during cleaning time of (about 2 minutes only), until drains become clear.

Advantages of Solid Cleaning:
1. No reduction in RPM, thus no effect on scheduled voyage.
2. No water required, thus no corrosion and thermal stresses.
3. Cleaning time, shortened to about 2 minutes only.
4. Charcoal does not wear down the Turbine Blades.
5. Combustion residues and hard particles, effectively removed.

Turbocharger surging:
1. Pumping of air back to compressor, due to sudden pressure drop in compressor, below delivery pressure.
2. Prolonged surging may cause damage to compressor, thus engine speed should be lowered down until surging vanished.
3. Then faults corrected before running again full speed.
Causes:
1. One or two cylinders stop firing.
2. Faulty fuel pump or fuel valve.
3. Scavenge fire or exhaust trunk fire.
4. Sudden load change, when pitching in bad weather.
5. Dirty nozzle rings, turbine blades, impeller blades.
6. Weight loss of turbine blades due to impingement attack by Catfines.
7. Dirty blower air suction filter.
8. Incorrect matching of T/C to engine.

TC Over-run:

Causes:
1. Happened in constant pressure turbo-charged engine.
2. Caused due to fire and/or detonation of scavenge space.
3. Exhaust trunk fire due to accumulation of leaked or excess LO and unburned fuel.
Effects:
1. TC bearings, casing damaged.
2. ER fire.
Prevention:
1. Scavenge space regular cleaning.
2. Exhaust gas pipe regular cleaning.
3. Maintain complete combustion of fuel.
4. Liner, piston and rings, fuel valves, cylinder lubrication, maintained in good order.
5. Avoid operating ME under reduced load for long term.

Turbocharger Overhauling: [VTR 161, 201, 251, 321]

1. Drain bearing LO.
2. Remove bearing cover, oil suction pipe, as per Maker’s Instruction.
3. Take ‘K’ value, and compare the value with stamped one on bearing cover.
4. Take out locknuts (hexagonal screws), lubricating disc, and bearings from both sides.
After removing Rotor shaft:
1. Decarbonize Turbine and Blower blades, and check the blade condition.
2. Check Labyrinth seals.
3. Check bearing clearances: 0.2 ~ 0.3 mm for Axial: 0.15 ~ 0.2 mm for Radial:
4. Check Nozzle Ring condition.
After refitting Rotor assembly:
1. Push Rotor from Turbine side to Blower side, and measure ‘K₁’ at Blower side.
[‘L’ = 0, at this time]
2. Push Rotor from Blower side to Turbine side, and measure ‘K₂’ at Blower side.
[‘M’ = 0, at this time]
After adjusting Rotor’s smooth optimum rotation:
1. Secure the locknut (hexagonal screw) of Blower side bearing.
2. Measure ‘K’ value at Blower end. [By Depth Micrometer or Calliper and Straight Edge].
3. Calculate ‘L’ and ‘M’ values.
[L = K – K₁] and [M = K₂ – K] and compare them with actual values.
Safety Devices in Machinery Space:

Safety devices on ME:
1. Crosshead bearing temperature sensor and alarm. (Slow down)
2. Main bearing temperature sensor and alarm. (Slow down)
3. LO return line temperature sensor and alarm. (Slow down)
4. Oil mist detector, for crankcase. (ME stopped)
5. Scavenge air temperature sensor and alarm. (Slow down)
6. High exhaust temperature sensor and alarm. (Slow down)
7. High FW temperature sensor and alarm. ( Slow down / ME stopped)
8. Low LO pressure alarm. (Slow down)
9. Low FW pressure alarm. (Slow down)
10. Turning Gear interlock.
11. Overspeed trip.
12. Emergency Manual Stop.
13. Micro computerised Safety Panel for Auto Slow down and Shut down arrangements.
14. Relief Valves on:
a) Cylinder head.
b) Scavenge trunk
c) Crankcase
d) Fuel pump and system
e) Start air line
15. Cylinder Lubricator failure alarm and Cylinder oil no-flow alarm.

Safety devices on Electrical Heaters: FO, LO.
1. HT cut-out switch, which switch off the supply.
2. Temperature sensor and auto switching device.

Safety devices on AC Main Switchboard:
1. Over current relay.
2. Reverse power relay
3. Short circuit relay
4. Preferential trip.

Windlass safety devices:
1. Overload [thermal switch]
2. Over speed trip
3. Slipping clutch.

Winches brake adjustment: Adjust the distance between friction plate and pressure plate.

Lifeboat safety devices:
1. Limit Switch [while lifting]
2. Centrifugal Brake [while lowering]

Safety devices on Steering Gear:
1. Low oil level alarms on each power unit reservoir tanks.
2. Overload alarm.
3. Power failure alarm.
4. Relief Valves in power unit hydraulic system and telemotor unit hydraulic system.
(Set pressure 20 – 30% above Normal Working Pressure.)
5. Double shock valves. (Set to lift at about 100 bar, 10% above NWP: allowed rudder to give way when subjected to severe shock from heavy sea.)
6. Suitable working access to Steering Gear Room and Control, with guardrails and non-slip surface.
7. Quick response in 30 sec. from hard over to hard over, at full speed.
8. A fixed oil storage system.

Safety devices on Main Air Compressor:
1. Bursting Disc on Intercooler: (At waterside)
2. Bursting Disc and Fusible Plug (121°C) on Aftercooler
3. Automatic Moisture Drain Valve.
4. Relief valves on LP and HP stages. (Set to lift at 10% rise above normal stage pressure.)
5. Cooling water supply failure alarm.
6. Low LO pressure alarm.
7. Relief valve on crankcase LO pump.
8. Delivery air HT alarm on Aftercooler outlet. (Max. 93°C)
{LP discharge pressure 4 bars: HP discharge pressure 30 bars:
Intercooler inlet air 130°C: Intercooler outlet air 35°C:
Aftercooler inlet air 130°C: Aftercooler outlet air 35°C:
Intercooler is single pass type: Aftercooler, double pass U-tube type:}

Safety devices on Main Air Bottle:
1. Fusible plug.
2. Pressure Relief Valve
3. Low Air Pressure alarm.
4. Atmospheric Relief Valve.
5. Automatic or remote control Moisture Drain Valve.

Safety devices on Boiler:
1. Two nos. of Safety Valves.
2. Low and high Water Level alarms with transmitter.
3. Low and high FO Temperature alarms.
4. Low FO Pressure alarm.
5. Low Steam Pressure alarm.
6. Easing Gears on Safety Valves.
7. Fusible Plugs.
8. 2 Water Level Gauge Glasses.
9. Remote Water Level Indicators.
10. Flame Failure alarm.
11. Smoke Density alarm.
12. Air/fuel Ratio alarm.

Safety devices on Fridge Plant and Compressor:
1. Liquid Shock Valve on Cylinder Head.
2. Busting Disc on Cylinder Head, between Suction and Discharge manifold.
3. Gas LP cut-out.
4. Gas HP cut-out.
5. LO LP cut-out.
6. CW LP cut-out.
7. Relief Valve on Condenser.
8. Bursting Disc on Condenser. (if fitted)
9. Non-return Check Valves on each gas return line to Compressor.

Miscellaneous Calculations:

Specific Fuel Oil Consumption, SFOC.

SGc = Corrected specific gravity of fuel at measuring point temperature;

SGb = Specific gravity of bunker;
(Should be taken from lab report, if not taken from bunker note at 15°C )

T = Fuel oil temperature at measuring point.

SGc = SGb – [ 0.00064 (T– 15) ]

kW = Output of engine in kW.

Let daily fuel consumption is = C litres/day (obtained from Flow Meter reading)
= C/10³ m³/day
= C/10³ x SGc MT/day
= C/10³ x SGc x 10³ kg/day
= C x SGc x 10³ gm/day

C x SGc x 10 ³
SFOC = gm / kW hr
24 x kW

C x SGc x 10 ³
SFOC = gm / bhp hr
24 x BHP

This initial specific fuel consumption should be corrected for 3 factors:
i. Difference between actual scavenge air temperature and system standard of 45°C.
ii. Difference between actual turbo blower air inlet temperature and
system standard of 27°C.
iii. The net specific energy of fuel .

If daily fuel consumption is = C MT/day

C x SGc x 10⁶
SFOC = gm / kW hr
24 x kW
Specific Cylinder Lubricating Oil Consumption:

qa = Actual feed rate, gm / kW-hr.
Q = Measured value, litre / day
r = SGc, Corrected specific gravity of oil at measuring point temperature.
Le = Engine output, in kW

Q x 1000 x r
qa = gm / bhp hr
24 x Le

Slip Calculation:

P = Pitch in meter
N = Total revolutions/ day ( N = 60 x 24 x r.p.m. )
Theoretical distance = ( P x N ) / 1852 Nautical miles per day.

Theoretical Distance  Actual Distance (Noon to Noon)
Slip % = x 100
Theoretical Distance

What is API scale of measurement? [FPS system]

Bunker Specific Gravity my be converted to degree API by the formula:

141.5
Degree API = – 131.5
Sp.Gr.

Degree API may be converted to Specific Gravity by:

141.5
Sp.Gr. =
at 15°C(59°F) 131.5 + degree API

Use Volume Correction Factor as per API gravity with exact oil temperature
at bunkering time.
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Gottiflava on 1/20/2020(UTC)
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