Marine Engineering Study Materials

Procedure for Turbocharger Overhaul

Overhauling is carried out as per planned maintenance of turbochargers. The procedure for overhauling diesel engine turbocharger is explained below.

1. Lock off the engine staring mechanism.
2. Remove the turbocharger air filter.
3. Drain off the oil from both drain plugs.
4. Remove the bearing covers from both sides.
5. Remove the locking wires.
6. Unscrew the hexagon screws and remove oil suction pipes.
7. Tighten again the hexagon screws of the bearing boxes.
8. Check the deflection of the divergent nozzle by using pick tester and magnet stand.
9. Remove the divergent nozzle by screw driver.
10. Measure the K value at the blower side by using depth micrometer or caliper and straight edge.
11. Lock the rotor with special tool.
12. Extract the lubricating disc.
13. Extract the both bearings by bearing extractor.
14. The various parts should be warped in waxed paper to protect them against dirt and moisture.

Checks on Turbocharger while Overhauling

1. Check the deflection of divergent nozzle.
2. Measure the K value at blower side.
3. Change the bearing on both sides with the new one (because bearing service life is same as turbocharger overhauling time).
4. Clean blower and turbine side with chemical and inspect carefully.
5. Check the labyrinth seal.
6. Made clear the labyrinth seal air line
7. Check the casing for crack & wear
8. Blade condition
9. After reassembled, check Static Balance
10. Check Impeller and Casing clearance

 When will you change turbocharger bearing ?

1. As per Running Hour
2. As per clearance
3. When damaged
4. When vibration is heavy

How to check deflection of divergent nozzle ?

1. By using Pick tester &
2. Magnet stand

What is the main purpose of turbocharger water washing ?

• To ensure efficient functioning of turbocharger.
• To protect the compressor and turbine from contamination (Deposits).

Disadvantages of turbocharger water washing to turbine side ?

• Engine speed has to lower.
• Thermal stress and corrosion usually occurred.
• Longer cleaning time.
• Very fine hard deposits and residues cannot be removed easily with water washing.

Advantages of solid (crystal) cleaning or grit washing ?

• Not required to reduce engine rpm, thus not affect on scheduled voyage
• No used of water, so no corrosion and thermal stress.
• Cleaning time is short.
• Not wear turbine blade.
• Effectively remove combustion residues and hard particle.

How will you carry out turbocharger turbine and blower side water washing ?

Blower side water washing

1. It can be done when M/E on full load.
2. Fill up the warm fresh water to hopper and closed the cover.
3. Open the valve and water will flow into the blower casing and mechanically attack the blower blades and clean the deposit.
4. Close the valve, open the cover and check the cleaning water must be empty.

Turbine side water washing procedure

1. Turbine side water washing can be made with hot fresh water.
2. Inform to the bridge
3. Reduce the M/E rpm to recommended speed and hence turbocharger rpm.
4. Check the water washing injection nozzle if fitted. (directly aim to the exhaust grips before entering to the turbocharger)
5. Open turbocharger drain valve.
6. Open the water supply about 1 bar to turbine side.
7. Water washing must be made until the clean water comes out.
8. Close the water supply and remove the nozzle.
9. Exhaust side drain can be closed after all water is drained out and dried.
10. Inform to the bridge and increase the M/E rpm gradually to sea speed.
11. The turbine side water washing is usually at departure after manoeuvring time.
12. For usual practice cleaning is done at every 500 hr, running hour depending on the cleanliness of the turbocharger .

Grit Washing or Dry Cleaning of Turbocharger

1. Turbine side cleaning is superseded by walnut shell, with grain size of 12 to 34 mesh 
2. No speed reduction required and cleaning can be done at full speed, once every day
3. Compressed air of (3 -5 bar) 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 (about 2 minutes only) 

What measurements are taken during auxiliary engine turbocharger overhaul ?

• K value, it is a distance between the rotor shaft end and the flange of bearing cover measure at blower side (axial clearance).
• Check radial clearance (at plane bearing), by placing clock gauge on the shaft from the top and clamp by screw driver from bottom, record the clearance.
• Rotor and Casing clearance (for new casing or new rotor) (L & M values)

How to measure turbocharger axial and radial clearance ?

Axial Clearance

• Push the shaft by screw jack and measure by Depth Gauge (0.2 – 0.3 mm)

Radial Clearance 

• Lift the shaft radially and measure by Dial Gauge (0.15 – .02 mm)

Why turbocharger exhaust outlet lower than inlet temperature ?

• Some exhaust gas heat and pressure energy is transferred to mechanical rotating energy for turbocharger, thus pressure become decrease and temperature lower.

What will occur is oil leak in turbocharger system ?

• If oil is leaked into the air system the cooling surface are covered with oil which are insulated & cooling efficiency will be reduce (ie. Scavenge temperature drop; Exhaust temperature high)
• Also there will be deposits on the blower and blower efficiency will be reduced
• If oil leaked into exhaust side, Carbon deposits on the nozzle & turbine blade. It cause surging, reduces blower efficiency and fire in the exhaust piping (uptake fire)

Turbocharger Over Run

Causes

• Happens in constant pressure turbo charged engine
• Caused due to fire and or detonation of scavenge space
• Exhaust trunk fire due to accumulation of leaked or excess lube oil and unburned fuel

Effects

• Turbocharger bearings, casing damage
• E/R fire

 Prevention

• Scavenge space regular cleaning
• Exhaust gas pipe regular cleaning
• Maintain complete combustion of fuel
• Liner, piston and rings, fuel vales, cylinder lubrication, maintained in good order
• Avoid operating M/E under reduced load for long term

Causes of Turbocharger Vibration

• Unbalancing
• Bearing defects
• Deposits in nozzle ring
• Impingement
• Surging, Scavenge Fire, Overloading

 Reference:

Oral Guide by – MIN ZAR TAR