Answer EKM Question 54
Q54. A. A number of main engine cylinder covers have been subjected to cracking during the preceding four months:
i. Explain possible reasons for this cracking;
ii. State with reasons the action you, as Second Engineer, would take in order to reduce the possibility of future cylinder cover cracking.
B. Cylinder liner wear has increased appreciably during the past six months. Write a brief report to the engineering superintendent concerning this matter explaining the possible causes the immediate action taken to deal with the problem and the action you, as Second Engineer, intend to take in order to reduce the risk of future incidents.
Answer: A. (i) Factors that tend to cause distortion of a cylinder heads:
The factor that tend to cause distortion of the cylinder head are:
(a) Compressive and bending stresses due to gas forces.
(b) Undue thermal stresses.
(b) Over tightening.
Small surface cracks sometimes found on the underside of the cylinder cover are due to intense local heating during combustion process, causes of which may be attributed to improper design, material or operating conditions.
A critical region is around the valve seat, air starting valve pocket and fuel injector pocket, which extend in radial direction. These may be caused by improper cooling due to scale deposit on the heat transfer surface.
(ii) Action to be taken to reduce the possibility of future cylinder cover cracking:
(a) Use of proper fuel: The fuel must be used as per the maker recommendations, deviation of which is troublesome. Care should be taken while ordering the fuel. Although a proper grade of fuel is been supplied, it is to be stored in a separate tank and avoid mixing with the old fuel onboard, before using the fuel it must be purified well and any contamination must be removed.
(b) Minimizing thermal stresses: Cooling of the cylinder cover causes a temperature difference on either side of the metal, this causes thermal stress and crack the metal. This problem can be avoided by maintaining the engine cooling water temperature within the allowed range. Engine must be preheated before starting and overloading should be avoided.
(c) Proper torque for tightening the Nuts: While re-tightening the cylinder head holding nuts, the recommended values must be consulted from the manual. Uneven or over tightening of the nuts keep the head stressed and in addition the gas forces will cause it to deform.
B. Brief report:
To
The engineering superintendent
Subject: Possible causes and remedial actions of liner wear down.
Dear sir,
Causes and types of liner and piston ring wear:
1. Corrosive wear:
During combustion any sulphur in fuel burns to form sulphur oxides which normally escape harmlessly with the exhaust gases. However if there is any dew formation or condensation of water, for example due to engine load or over cooling and lowering of liner-wall temperature, the sulphur oxides and water combine to form acids which can attack the liner and piston ring Surfaces causing corrosive wear. Acid formation can be avoided or reduced by maintaining a high jacket cooling water return temperature (80-85 deg cel.) and avoiding running the engine at low load over a prolonged period. Some engine makers recommend special insulation to be applied on liner cooling surface to avoid over-cooling in case it is intended to 'slow steam' the ship for a prolonged period. Cylinder lubricating oil has alkaline additives to neutralize the acids and prevent corrosion.
2 Abrasive wear:
Abrasive wear is due to mechanical rubbing or grinding action between the liner and piston rings in the presence of abrasive substances including carbonaceous deposits formed during combustion and catalytic fines and other impurities in fuel. A good quality fuel oil and efficient filtration and centrifuging of the fuel can remove most of the abrasive substances and reduce abrasive wear to a large extent.
3. Adhesive wear (also called scuffing or micro-seizure):
It takes place when there is metal to metal contact between liner and piston rings due to absence of cylinder lubricating oil film. The rubbing spots are heated to a very high temperature causing momentary fusion, followed immediately by separation leaving tear on surface. Adequate cylinder lubrication with proper viscosity oil and lower liner wall temperature help to maintain proper oil film thickness between the liner and piston rings and reduce adhesive wear.
2nd engineer
MV XYZ
i. Explain possible reasons for this cracking;
ii. State with reasons the action you, as Second Engineer, would take in order to reduce the possibility of future cylinder cover cracking.
B. Cylinder liner wear has increased appreciably during the past six months. Write a brief report to the engineering superintendent concerning this matter explaining the possible causes the immediate action taken to deal with the problem and the action you, as Second Engineer, intend to take in order to reduce the risk of future incidents.
Answer: A. (i) Factors that tend to cause distortion of a cylinder heads:
The factor that tend to cause distortion of the cylinder head are:
(a) Compressive and bending stresses due to gas forces.
(b) Undue thermal stresses.
(b) Over tightening.
Small surface cracks sometimes found on the underside of the cylinder cover are due to intense local heating during combustion process, causes of which may be attributed to improper design, material or operating conditions.
A critical region is around the valve seat, air starting valve pocket and fuel injector pocket, which extend in radial direction. These may be caused by improper cooling due to scale deposit on the heat transfer surface.
(ii) Action to be taken to reduce the possibility of future cylinder cover cracking:
(a) Use of proper fuel: The fuel must be used as per the maker recommendations, deviation of which is troublesome. Care should be taken while ordering the fuel. Although a proper grade of fuel is been supplied, it is to be stored in a separate tank and avoid mixing with the old fuel onboard, before using the fuel it must be purified well and any contamination must be removed.
(b) Minimizing thermal stresses: Cooling of the cylinder cover causes a temperature difference on either side of the metal, this causes thermal stress and crack the metal. This problem can be avoided by maintaining the engine cooling water temperature within the allowed range. Engine must be preheated before starting and overloading should be avoided.
(c) Proper torque for tightening the Nuts: While re-tightening the cylinder head holding nuts, the recommended values must be consulted from the manual. Uneven or over tightening of the nuts keep the head stressed and in addition the gas forces will cause it to deform.
B. Brief report:
To
The engineering superintendent
Subject: Possible causes and remedial actions of liner wear down.
Dear sir,
Causes and types of liner and piston ring wear:
1. Corrosive wear:
During combustion any sulphur in fuel burns to form sulphur oxides which normally escape harmlessly with the exhaust gases. However if there is any dew formation or condensation of water, for example due to engine load or over cooling and lowering of liner-wall temperature, the sulphur oxides and water combine to form acids which can attack the liner and piston ring Surfaces causing corrosive wear. Acid formation can be avoided or reduced by maintaining a high jacket cooling water return temperature (80-85 deg cel.) and avoiding running the engine at low load over a prolonged period. Some engine makers recommend special insulation to be applied on liner cooling surface to avoid over-cooling in case it is intended to 'slow steam' the ship for a prolonged period. Cylinder lubricating oil has alkaline additives to neutralize the acids and prevent corrosion.
2 Abrasive wear:
Abrasive wear is due to mechanical rubbing or grinding action between the liner and piston rings in the presence of abrasive substances including carbonaceous deposits formed during combustion and catalytic fines and other impurities in fuel. A good quality fuel oil and efficient filtration and centrifuging of the fuel can remove most of the abrasive substances and reduce abrasive wear to a large extent.
3. Adhesive wear (also called scuffing or micro-seizure):
It takes place when there is metal to metal contact between liner and piston rings due to absence of cylinder lubricating oil film. The rubbing spots are heated to a very high temperature causing momentary fusion, followed immediately by separation leaving tear on surface. Adequate cylinder lubrication with proper viscosity oil and lower liner wall temperature help to maintain proper oil film thickness between the liner and piston rings and reduce adhesive wear.
2nd engineer
MV XYZ
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