Source: MAN Diesel (MAN-B&W-K98MC)
Cylinder liner wears:
1) Normal frictional wear: Due to metal to metal contact with high surface asperities under
marginal lubrication condition.
2) Abrasive wear: Due to presence of hard foreign particles from fuel, LO, and air.
3) Corrosive wear:Due to H₂SO₄ acid attack owing to sulphur within fuel. Only 0.1% of sulphur content causes corrosive wear, like hot and cold corrosion, and the rest carried away by exhaust gas. Sulphuric acid dew point = 120΄C to 160΄C.
1) Normal frictional wear: Due to metal to metal contact with high surface asperities under
marginal lubrication condition.
2) Abrasive wear: Due to presence of hard foreign particles from fuel, LO, and air.
3) Corrosive wear:Due to H₂SO₄ acid attack owing to sulphur within fuel. Only 0.1% of sulphur content causes corrosive wear, like hot and cold corrosion, and the rest carried away by exhaust gas. Sulphuric acid dew point = 120΄C to 160΄C.
Hot corrosion occurs at 460 – 570΄C.
Due to HCl acid attack, because of salts in air, charge air cooler leakage,
sea water in fuel and LO.
Due to HCl acid attack, because of salts in air, charge air cooler leakage,
sea water in fuel and LO.
Other related causes:
1. Unsuitable liner material.
2. Incorrect ring clearance.
3. Misalignment of piston and liner.
4. Insufficient LO or improper arrangement of cylinder lubrication.
5. Cylinder oil having too low viscosity or alkalinity.
6. Cylinder oil containing abrasive particles.
7. Using of low sulphur fuel, in conjunction with high TBN cylinder oil.
8. Improper grade of fuel, and improper combustion.
9. Improper running-in, without high cylinder oil feed rate.
10. Overloading of engine.
11. Too low scavenge air temperature, leading to dew point corrosion.
1. Unsuitable liner material.
2. Incorrect ring clearance.
3. Misalignment of piston and liner.
4. Insufficient LO or improper arrangement of cylinder lubrication.
5. Cylinder oil having too low viscosity or alkalinity.
6. Cylinder oil containing abrasive particles.
7. Using of low sulphur fuel, in conjunction with high TBN cylinder oil.
8. Improper grade of fuel, and improper combustion.
9. Improper running-in, without high cylinder oil feed rate.
10. Overloading of engine.
11. Too low scavenge air temperature, leading to dew point corrosion.
Types of wear:
Scratching: Develop in the region of ring travel, due to small particles entrapped between the bore and rings.
Scoring: Confined to the region of ring travels and may extend to the region, swept by piston. Origin is similar to scratching.
Scuffing: Develop in ring travel, on thrust side of liner, depending on lubrication efficiency, speed and loading.
Clover Leaf Pattern: Irregular, oval or elliptical pattern of longitudinal corrosive wear, at several points around liner, concentrated between lubrication orifices or the points of LO quills. It is due to incorrect cylinder oil feed rate and acidic effect of combustion products or too low TBN cylinder oil.
– In actual practice, wear never takes place concentrically, and it depends on heel and trim of the ship in service, and effective guide clearance.
– In tankers and bulk carriers, where long ballast passage are made with the trim aft, maximum wear will be in the fore and aft plane, and especially on aft side of the liner.
– In tankers and bulk carriers, where long ballast passage are made with the trim aft, maximum wear will be in the fore and aft plane, and especially on aft side of the liner.
Wear rate:
1. Liner wear rate is high during running-in period, after which it becomes uniform within most of its service life.
2. Finally, wear rate increases rapidly as wear becomes excessive, and due to difficulties in maintaining the rings, gas tight.
3. Wear rate can be high about 0.75 mm / 1000 hrs. in large slow speed engines, using residual fuel containing 1.5% of sulphur, in excess.
4. Wear rate being lower about 0.02 mm / 1000 hrs. in medium speed engines, due to burning low sulphur fuel oil.
5. When Vanadium is added during manufacturing, wear rate significantly reduced to the range, 0.025 mm / 1000 hrs. ~ 0.5 mm / 1000 hrs.
6. Maximum allowable wear: = 0.7 % to 1.0% of original bore, for large output engine.
1. Liner wear rate is high during running-in period, after which it becomes uniform within most of its service life.
2. Finally, wear rate increases rapidly as wear becomes excessive, and due to difficulties in maintaining the rings, gas tight.
3. Wear rate can be high about 0.75 mm / 1000 hrs. in large slow speed engines, using residual fuel containing 1.5% of sulphur, in excess.
4. Wear rate being lower about 0.02 mm / 1000 hrs. in medium speed engines, due to burning low sulphur fuel oil.
5. When Vanadium is added during manufacturing, wear rate significantly reduced to the range, 0.025 mm / 1000 hrs. ~ 0.5 mm / 1000 hrs.
6. Maximum allowable wear: = 0.7 % to 1.0% of original bore, for large output engine.
Wear pattern:
» Maximum wear is at upper limit of top ring travel, at the top of piston stroke.
» This reduces towards the lower end of the stroke, but will increase in way of exhaust and scavenge ports.
» Maximum wear is at upper limit of top ring travel, at the top of piston stroke.
» This reduces towards the lower end of the stroke, but will increase in way of exhaust and scavenge ports.
Reasons of maximum wear at top of the stroke:
1. Maximum gas load behind the top ring.
2. It is a hottest region.
3. Oil film viscosity is low, and liable to breakdown under high load and high temperature.
4. Abrupt change in direction of piston rings, at dead ends of reciprocating motion.
5. More liable to be attacked by acids.
1. Maximum gas load behind the top ring.
2. It is a hottest region.
3. Oil film viscosity is low, and liable to breakdown under high load and high temperature.
4. Abrupt change in direction of piston rings, at dead ends of reciprocating motion.
5. More liable to be attacked by acids.
Reason of maximum wear around the ports:
» Due to leakage of hot gases, past the top ring into the ports, and these gases tend to burn off oil film.
» Due to leakage of hot gases, past the top ring into the ports, and these gases tend to burn off oil film.
Results of proper well-run ship:
– Good liner wear rate: < 0.1 mm / 1000 hrs. after running-in period.
– Good ring wear rate: < 0.4 mm / 1000 hrs.
– Economical level of cylinder oil feed rate: < 1.0 gm/Bhp/hr. after running-in period.
– Good liner wear rate: < 0.1 mm / 1000 hrs. after running-in period.
– Good ring wear rate: < 0.4 mm / 1000 hrs.
– Economical level of cylinder oil feed rate: < 1.0 gm/Bhp/hr. after running-in period.
Timed lubrication:
1. Lubricators of each cylinder are synchronized with engine to provide timed lubrication.
2. Cylinder oil is fed, at the time when top two piston rings pass the oil feed points, in the cylinder during piston upstroke. [4/s and 2/s Uni-flow engines]
3. Loop scavenge Sulzer RND engine use accumulator system of timed lubrication.
4. Accumulator provides constant oil pressure, which is greater than scavenge air pressure, with uniform supply at every period, around TDC and BDC positions.
5. In this way, oil is delivered to quills, only when low pressure and temperature prevails on running surface of cylinder liner.
6. 8 supply points at top, and 1 point for scavenge and 1 point for exhaust ports at bottom.
1. Lubricators of each cylinder are synchronized with engine to provide timed lubrication.
2. Cylinder oil is fed, at the time when top two piston rings pass the oil feed points, in the cylinder during piston upstroke. [4/s and 2/s Uni-flow engines]
3. Loop scavenge Sulzer RND engine use accumulator system of timed lubrication.
4. Accumulator provides constant oil pressure, which is greater than scavenge air pressure, with uniform supply at every period, around TDC and BDC positions.
5. In this way, oil is delivered to quills, only when low pressure and temperature prevails on running surface of cylinder liner.
6. 8 supply points at top, and 1 point for scavenge and 1 point for exhaust ports at bottom.
Timed lubrication has little merits, because:
1. It requires very rapid injection of oil at correct time, with correct amount, and pressure.
2. It is discharging through very small bore, with long pipes to various oil feed points.
3. Having a non-return valve at the top of lubricator, hence it complicates the timed injection.
4. The hot combustion gases tend to carbonize the oil, and block the orifices.
1. It requires very rapid injection of oil at correct time, with correct amount, and pressure.
2. It is discharging through very small bore, with long pipes to various oil feed points.
3. Having a non-return valve at the top of lubricator, hence it complicates the timed injection.
4. The hot combustion gases tend to carbonize the oil, and block the orifices.
Reduced lubrication effects:
1. Promote wear of liner and rings.
2. Over-heating of local area causes micro-seizure, due to lack of boundary lubrication.
3. Consequently, major damage to liner and piston.
1. Promote wear of liner and rings.
2. Over-heating of local area causes micro-seizure, due to lack of boundary lubrication.
3. Consequently, major damage to liner and piston.
Excess lubrication effects:
1. Fouling of ring grooves and resulting ring zone deposits.
2. Leading to breakage of piston rings.
3. Consequently, loss of gas sealing effects and blow-by follows.
4. Scavenge space fouling and scavenge fire follows.
5. Also affecting combustion process.
6. Exhaust system and turbocharger fouling.
1. Fouling of ring grooves and resulting ring zone deposits.
2. Leading to breakage of piston rings.
3. Consequently, loss of gas sealing effects and blow-by follows.
4. Scavenge space fouling and scavenge fire follows.
5. Also affecting combustion process.
6. Exhaust system and turbocharger fouling.
Cracks on cylinder liner: Causes:
1. Over-tightening of cylinder cover nuts.
2. Insufficient cooling.
3. Effects of scavenge fire.
4. High difference of working temperature.
5. Increasing of hoop stress in liner, due to slack tie bolts.
6. Misalignment of worn-out liner and piston.
7. Due to thermal stresses of metal, between exhaust ports and scavenge ports.
8. Improper fitting of liner.
9. Design failure.
1. Over-tightening of cylinder cover nuts.
2. Insufficient cooling.
3. Effects of scavenge fire.
4. High difference of working temperature.
5. Increasing of hoop stress in liner, due to slack tie bolts.
6. Misalignment of worn-out liner and piston.
7. Due to thermal stresses of metal, between exhaust ports and scavenge ports.
8. Improper fitting of liner.
9. Design failure.
Removing and refitting the liner:
Before removing:
1. Immobilization permit taken from port authority.
2. Vessel in upright position.
3. Lifting gears and tools in good working order.
4. All spares are ready.
5. Persons grouped for assigned jobs.
Before removing:
1. Immobilization permit taken from port authority.
2. Vessel in upright position.
3. Lifting gears and tools in good working order.
4. All spares are ready.
5. Persons grouped for assigned jobs.
Removing the liner:
1. Drain CW from cylinder jacket.
2. All lubricator quills removed.
3. Cylinder cover, piston and stuffing box removed in usual way.
4. Cover the piston rod stuffing box seating with special cover.
5. If liner is to be reused, liner wear should be measured and recorded.
6. Position of liner, relative to cylinder jacket, properly marked.
7. CW outlet pieces to cylinder cover removed.
8. Attach the liner-withdrawing tool as per instruction, and tighten the upper nut until liner comes in contact with upper supporting bar [strong back bar].
9. With overhead crane and sling arrangement, liner is drawn out.
1. Drain CW from cylinder jacket.
2. All lubricator quills removed.
3. Cylinder cover, piston and stuffing box removed in usual way.
4. Cover the piston rod stuffing box seating with special cover.
5. If liner is to be reused, liner wear should be measured and recorded.
6. Position of liner, relative to cylinder jacket, properly marked.
7. CW outlet pieces to cylinder cover removed.
8. Attach the liner-withdrawing tool as per instruction, and tighten the upper nut until liner comes in contact with upper supporting bar [strong back bar].
9. With overhead crane and sling arrangement, liner is drawn out.
Before refitting:
1. If old liner is to be reused, clean thoroughly.
2. Landing surface of quills checked for damage and carbon deposits in oil holes cleaned.
3. Rubber sealing ring grooves, cleaned with old round file until to bare metal.
4. Surface inside jacket, coated with anti-corrosive paint, and sitting surfaces cleaned.
5. Sharp edges inside jacket, chamfered slightly to prevent cutting rubber sealing rings.
6. If new liner is to be fitted, gauged before fitting.
7. New liner is to be lowered down into position, without sealing rings fitted, to ensure it is correct size. Liner should not only drop freely by its own weight, but there should be slight radial clearance between liner and jacket to allow for expansion.
8. Radial clearance at lower end, ≮ 0.2 mm for 750 mm bore liner.
9. Radial clearance at top, ≮ 0.001 mm / mm of liner bore.
10. Rubber sealing rings should grip firmly around liner, and a 10% stretch would be adequate.
11. If there is no original reference mark on liner, quills should be fitted and mark the correct position of liner relative to cylinder jacket.
12. Remove the liner again and sealing rings fitted.
1. If old liner is to be reused, clean thoroughly.
2. Landing surface of quills checked for damage and carbon deposits in oil holes cleaned.
3. Rubber sealing ring grooves, cleaned with old round file until to bare metal.
4. Surface inside jacket, coated with anti-corrosive paint, and sitting surfaces cleaned.
5. Sharp edges inside jacket, chamfered slightly to prevent cutting rubber sealing rings.
6. If new liner is to be fitted, gauged before fitting.
7. New liner is to be lowered down into position, without sealing rings fitted, to ensure it is correct size. Liner should not only drop freely by its own weight, but there should be slight radial clearance between liner and jacket to allow for expansion.
8. Radial clearance at lower end, ≮ 0.2 mm for 750 mm bore liner.
9. Radial clearance at top, ≮ 0.001 mm / mm of liner bore.
10. Rubber sealing rings should grip firmly around liner, and a 10% stretch would be adequate.
11. If there is no original reference mark on liner, quills should be fitted and mark the correct position of liner relative to cylinder jacket.
12. Remove the liner again and sealing rings fitted.
Refitting the liner:
1. Soft soap or similar lubricant to be applied to rubber sealing rings for easy fitting.
2. Fit in correct position as per instruction.
3. New liner re-gauged after final landing to check any distortion and recorded.
4. Refit quills and test lubrication. All parts refitted in usual way.
5. Fill cylinder jacket and check water-tightness under pressure.
1. Soft soap or similar lubricant to be applied to rubber sealing rings for easy fitting.
2. Fit in correct position as per instruction.
3. New liner re-gauged after final landing to check any distortion and recorded.
4. Refit quills and test lubrication. All parts refitted in usual way.
5. Fill cylinder jacket and check water-tightness under pressure.
Running-in: During the first 10 ~ 20 hours:
1. Cylinder oil feed rate at maximum.
2. Engine load reduced.
3. Reduce oil feed rate to normal and increase the load stepwise.
4. Liner checked from inspection door and scavenge space, at first opportunity.
1. Cylinder oil feed rate at maximum.
2. Engine load reduced.
3. Reduce oil feed rate to normal and increase the load stepwise.
4. Liner checked from inspection door and scavenge space, at first opportunity.
Safety devices on Cylinder Cover
1. Indicator cock.
2. Cylinder head relief valve. [Setting 20 ~30% above normal working pressure.]
3. Safety Cap.
4. Flame Trap.
5. Exhaust gas thermometer.
1. Indicator cock.
2. Cylinder head relief valve. [Setting 20 ~30% above normal working pressure.]
3. Safety Cap.
4. Flame Trap.
5. Exhaust gas thermometer.
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