Situation:

On board a PCC an accident has been reported in Main Engine, a fire/Explosion took place in exhaust manifold and smoke emitting around scavenge and exhaust manifold area.

Summary of the incident:

Main Engine: MITSUBISHI 8 UEC 37 LA & Turbo-Charger: MET 42 SC

The vessel underway, Bridge control operation, an alarm sounded “Imperfect bridge control condition” followed by fire alarm. Engine stopped and engineers confirmed, after inspection, scavenge fire. On carrying out the required preventive measures for scavenge fire the engine re-started. The engine found to be unstable when increasing revolutions.

The only other observation prior failure noted to be the increase in lube oil consumption is little excessive than normal and investigations for loss of lube oil at under piston spaces, scavenge spaces, Lube oil purifier spaces or any external losses proved satisfactory operation.

The engine stopped and thorough inspection realized that turbocharger suffered from multiple damages on nozzle ring, rotor blades, and bearings and to some considerable extent the guide inlet casing.

The vessel dry docked about a month back and repairs carried out on main engine turbocharger, Inspections and cleaning done on exhaust manifold and scavenge spaces respectively.

The temporary repairs carried out on leaky piston crown o-rings of units 2 and 5, turbochargers, lube oil supply to turbocharger blanked and continued at 40% NCR.

Cause of Incident:

The destructive damages of complete turbocharger breakdown analysis ascribed to the following:

1) Primarily, due to Turbo charger over run, because of abnormal combustion on engine side and exhaust manifold explosion ( Excessive fire), and categorized further to:
- abnormal combustion
- Scavenge fire
- Lube oil leakage from piston crown
- Fuel valve defects
- Blow–by (worn cylinder liners, broken piston rings, Disabled maintenance schedules etc.,)
- Poor handling in continuous very low load operation.

2) As secondary, accident of contact between the moving and static part like ‘Thrust bearing’. Turbocharger damage due to thrust bearing, where the lube oil leaked and flowed into the exhaust passage and caught fire, resulting in total break down. The experiences are explained as:
- Thrust bearing- white metal on the main thrust bearing can becomes prematurely worn in a relatively short period of time.
- Thrust collar-this thrust collar bearing against thrust bearing can develop circular surface scars resembling the grooves of the record disk and worn excessively.

Counter Measures:

The Important remedial action is to review the engine operation and maintenance management.

1) Turbo-charger over running due to fire or explosion in Exhaust manifold. –Poor or abnormal combustion is the result of lack of identification of the defective engine Running parameters and implementation of the corrective actions required.

2) The following are some counter measures to prevent turbocharger over run, due to fire or Explosion in the exhaust manifold

  • a) Fire due to start failure – Limit the number of repeated continuous starts should be three.

b) Identify the start failure and rectify before the next successive starts – when repeated starts, temperature level in combustion chamber lowered, disabling the injected fuel ignition-ability, un-burnt fuel accumulated inside the exhaust pipe.

c) When engine is under continuous operation, poor combustion resulting in exhaust gas temperature deviation alarm, un-burnt fuel stagnant inside the exhaust pipe can cause the fire. At such important alarm sounded, a necessary remedial action to be implemented immediately.

d) Any speed increase of engine is disabled, due to poor combustion, It can be attributed to piston crown o-ring and cooling oil on top of piston crown top was then be carried to exhaust manifold, an immediate inspection of piston O-rings leak to be done and rectified.

e) Sequential fire in scavenge spaces can lead to fire in exhaust space, when load lowered, auxiliary blower cut-in automatically lead to secondary fire in exhaust manifold and further scavenge fire remedial action, restart and load increase operation another fire occurrence can lead to another fire or explosion can cause serious damage. A complete action is to be implemented for prevention of scavenge room fire.

3) The thrust bearing failure may be attributed to inadequate machining or assembly done on Thrust collar. However, the following are some remedial actions to prevent the risk of failure.

  • a) Strict observance of lube oil quality and management. When system oil is in use of turbocharger lubrication, Pay strict attention to deterioration of the oil characteristics. Attention required to maintain Lube oil purifiers ( through put and temperature), Filters (torn, holed, enlarged or deformed), Thoroughly examine the white metal condition and impurities.

b) Check lube oil inlet lines, Lube oil head tank internal surfaces for fouling and keep them in clean condition.

c) Stuffing box leaked lube oil, it is recommended that the oil drained to be disposed or incinerated and not to be re-used. For economical reasons to re-use, to be followed by strict thorough purification, CJC fine filtering and test the quality of purified oil for reuse, before shifting to sump.

d) Check the sealing air passage for fouling and keep them clean.

e) Adequate maintenance of major parts of turbo charger, strictly renew with new spares, since extremely precise finishing of surface on the thrust collar is required and the allowable limit of surface tilt on it is 10 micron.

f) Periodic inspection of clearance of thrust bearing. The thrust bearing wear down should be measured at every 7000 hours running schedule.

posted 18 Jun '17, 08:13

June 18, 2017, 8:13 a.m.
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