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Cylinder liner low temperature corrosion

2022-11-03

Low-temperature corrosion is the sulfur dioxide and sulfur trioxide generated by the sulfur in the fuel during the combustion process in the cylinder, both of which are gases, which combine with water to generate hyposulfuric acid and sulfuric acid (when the cylinder wall temperature is lower than their dew point), thereby forming low-temperature corrosion. .
 
When the total base number of the cylinder oil is too low, paint-like deposits will appear on the surface of the cylinder liner between each oil injection point, and the surface of the cylinder liner under the paint-like substance will be darkened by corrosion. When chrome-plated cylinder liners are used, white spots (chromium sulfate) will appear in the corroded areas.
 
The factors that affect the low temperature corrosion are the sulfur content in the fuel oil, the alkali value and the oil injection rate in the cylinder oil, and the water content of the scavenging gas. The moisture content of the scavenging air is related to the humidity of the air and the scavenging air temperature.
 
When the ship sails in the high-humidity sea area, pay attention to check the discharge of the condensed water of the air cooler.
The setting of the pumping temperature has duality. The lower temperature can play the role of "dry cooling" scavenging, the relative humidity of the scavenging air will decrease, and the power of the main engine will increase; however, the low scavenging air temperature will affect the temperature of the cylinder wall. Once the temperature of the cylinder wall is lower than the dew point , low temperature corrosion will occur when the base value of the cylinder oil film on the cylinder wall is insufficient.
It is mentioned in the main engine service circular that when the main engine is running at low load, it is recommended to appropriately increase the scavenging temperature to avoid low temperature corrosion.
 
To increase the temperature of the main engine cylinder liner cooling water to reduce low temperature corrosion, MAN has used the LCDL system to increase the main engine cylinder liner cooling water to 120 °C to prevent low temperature corrosion.