Marine Engineering Study Materials

Crankcase Explosion on Ships – Marine Engineering

What is crankcase explosion ?

What are the causes of crankcase explosion ?

What is hot spot and why it occur ?

How will you know whether hot spot is there or not ?

  1. By hand feel to crankcase door
  2. Abnormal noise in crankcase.
  3. Irregular running of engine
  4. Bearing L.O temperature increase
  5. Alarm will operate when it reach at oil mist concentration 2.5 – 5% LEL
  6. Smelling & appearance of the dense oil mist when open breather pipe, drain cock.

How to prevent the crankcase explosion ?

 Preventive measure of crankcase explosion

  1. There should be adequate cooling of the engine.
  2. Proper purification and analysis of lube oil.
  3. Lube oil filter to be changed over & cleaned as per schedule.
  4. Ensure proper cylinder lubrication by checking the condition of piston, piston rings and liner through scavenge ports.
  5. Clean scavenge space as per schedule & drain scavenges space regularly.
  6. Maintain the stuffing box gland sealing in good condition.
  7. All running gears maintenance & checks to be carried out as per PMS.
  8. Be alert & rectify for any abnormal noise in crankcase.
  9. All safety trips & alarms fitted on M/E to be tried out for satisfactory.
  10. Proper watch on all running gears temperature & pressure to be maintained.
  11. Blow through all sampling tubes of Oil Mist Detector (OMD) regularly.
  12. Zero adjustment & sensitivity of OMD to be checked regularly.
  13. Check for oil leakage at crankcase explosion relief doors & check for the operation by hand.
  14. Check flame trap for cleanliness and intact condition.

What will be your action after detecting a hot spot ?

  1. Inform chief engineer & bridge
  2. Reduce the engine speed to reduce the heat generation
  3. Increase lubrication to the running surfaces
  4. Keep clear off crankcase relief door to prevent personnel injury, keep fire extinguisher ready and open skylight.
  5. Inform bridge, stop engine, open indicator cocks, engage turning gear and turn engine with lube oil circulation continuing to prevent engine seizure.
  6. After about 30 minutes when the engine is sufficiently cooled down, stop lube oil pumps and open crankcase door.
  7. Try to locate the hot spot by hand feeling over and by observation like change in colour.
  8. If the hot spot is located, prevent re-occurrence by making permanent repair.
  9. Make thorough inspection of crankcase.
  10. Pay particular attention to hot bearings, piston, bottom end bolts, guides and piston rod around stuffing box.
  11. Start lube oil pumps and check for proper flow of oil from every lubrication point.
  12. If everything is found normal, inform bridge, start the engine and gradually increase speed.
  13. Outside feel over sequence to be carried out for satisfactory operation.

What are crankcase safety devices ?

  1. Breather pipe with flame trap
  2. Crankcase exhaust fan
  3. Oil mist detector
  4. Crankcase relief doors
  5. Bearing temperature sensor
  6. L.O return temperature sensor
  7. Routine test on used L.O for viscosity, flash point and contamination.

Why is breather pipe fitted in the crankcase ?

Why crank case relief valve is fitted ?

What are the requirements of crankcase relief valves ?

  1. The internal combustion engine of cylinder diameter of 200 mm or a crankcase volume of 0.6 m3 and above shall be provide with crankcase relief valve of a suitable type with sufficient relief area.
  2. In small engine, cylinder diameter not more than 300mm, crankcase door of which are usually very strong. It may have relief valve or valves at its end.
  3. In large engine, cylinder diameter more than 300mm, require one relief valve to be placed on each crankcase door.
  4. Its free area should not be smaller than 45cm2 and there shall be minimum of 115cm2 /m3 of the gross crankcase volume.
  5. Spring setting for opening pressure is 0.07 bar at an internal pressure and will close when the pressure has been relieved.
  6. The valves open smartly and close positively and rapidly.

How would you test crankcase relief valve ?

What are the causes of bearing high temperature ?

  1. Improper viscosity of oil
  2. Insufficient lubrication
  3. Misalignment of shaft or bearings
  4. Foreign matters in oil
  5. Score in journal
  6. Poorly fitted bearing
  7. Improper oil clearance
  8. Whenever the bearing begins to heat up, check the lubrication whether it is clear, correct temperature and flow sufficient or not.

What is the blow past / blow by ?

What are the source of oil coming into air bottle ?

What point to be checked during crankcase inspection ?

Why oil mist detector is fitted ?

What are oil mist detector maintenance ?

How will you take action when oil mist detector alarm is on ?

Reference:

Oral Guide by – MIN ZAR TAR

Exit mobile version