This article will discuss the importance of crankcase inspection. It will cover safety precautions to be carried out before inspection, the procedure to carry out the inspection as well as explain the need for shaft grounding system.
A consult with chief engineer informs the master the crankcase inspection has been carried out at regular intervals. Normally this inspection is also carried out at every port when the vessel is set to sail for a long voyage, to ensure that the moving gears are in proper condition. By carrying out the crankcase inspection we can conclude the condition of the main bearing, lubrication points, and the crankshaft deflection.
Many operating faults arise when the lubrication is not perfect and the lubrication points are being chocked, improper lubrication can even cause a crankcase explosion due to the formation of hot spots. The bearing failure will also cause static and dynamic imbalance, and finally result in crank shaft deflection. Slackened connecting rod bolts will result in high stress concentration at the joints, continuous tension, and compression stress act while the engine is running and finally result in the failure of the bolts. It may cause severe damage to the engine parts as the connecting rod tries to fly inside the engine.
So to avoid these problems, the crankcase inspection is carried out to make sure that the engine is safe to run for a longer period of time.
Safety Precautions carried Out before Crankcase Inspection:
- Shutoff of main air staring valve and air bottle main valve.
- Open indicator cocks and engage turning gear.
- Ensure engine has been tuned for at least half an hour before stopping lube oil pump and cross head lubrication pump.
- Stop lube oil pumps and cross head oil pump and place the circuit breakers in off position.
- Post notice “Don’t start - Men at work”.
- Inform duty officer for propeller clearance.
- Open crankcase door and ventilate properly.
- Wear safety gear; e.g. helmet, boots, raincoat, gloves etc.
- Use safety lamps, torches and tools.
- All pockets should be emptied of contents and all tools taken inside must to be accounted for.
- One responsible person must stand outside.
Procedure to be carried out during Crankcase Inspection:
- Firstly check oil condition for any smell, discoloration or degradation.
- Turn the engine to BDC and start checking from under stuffing box area for any sign of black oil, an indication of stuffing box leaking.
- Check the piston rod surface for scoring marks and roughness.
- Check piston palm bolts and locking device for slackness and fretting.
- Check the guide and guide shoe bearing general condition and the area around frame where guide is attached for any visible cracks.
- Check that the guide shoe end cover bolts are in place and not slack.
- Check cross head bearing general condition.
- Evaluate top and bottom end of connecting rod bolt, nut and locking device for slackness, signs of fretting, etc.
- Check for sliding of bottom end bearing (axial movement) or floating of connecting rod.
- Check for slip of web and journal by checking the reference mark.
- Check web in the area of stress concentration and check tie bolt (bottom side).
- Check cross grider, area around main bearing and bearing keep for sign of cracks and check around main bearing.
- All bearings must be checked for silvery color (indicates bearing wiping).
- Check the surroundings of the oil pan area of all units for any sludge deposits, bearing metal pieces, etc.
- Check crank case relief door- wire mesh (should be wet), spring tension, sealing ring condition, etc.
- Check the teeth of transmission gear for sign of wear.
- Check chain drive for tightness.
- Use oil mist detector on sampling pipe to check for clear passage.
- Clear all the foreign materials from the crank case, and make sure all tools are accounted for.
- Start lube oil pump and cross head lubricating pump and check for the oil flow and distribution.
- Check crankcase door sealing condition and close the crankcase door.
- Inform chief engineer (for satisfactory checking of crank case) and duty officer.
Shaft Grounding System:
Shaft grounding is also one of the important factors to be checked along with the crankcase inspection, because it may result in spark erosion.
- Spark Erosion is caused by the voltage discharged between the main bearing and journal.
- The causes of this potential are the development of a galvanic element between the ship’s hull (from sea water) and the propeller shaft/ crank shaft.
- The voltage produced should be grounded; spark erosion occurs if it is not grounded.
- The oil film acts as a dielectric, so the puncture voltage in the bearing depends on the thickness of oil film.
- If the load increases, oil film thickness decreases.
- In early stages, the roughened areas can reasonable cause pitting erosion, but later as roughness increases, the small craters will scrape off and pick up the white metal, hence the silvery white appearance.
- Keep shaft voltage below 50mV.
- High voltage means shaft grounding has not been done properly
- Spark erosion only occurs between main bearing and journal.