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Water in Lube Oil
All modern engine lubricants are designed to remain stable in the presence of small amounts of water. Water contamination cannot realistically be avoided although its effects can be limited by good maintenance policies. It can enter the oil from condensation, leaking coolers and deck vents, blow-by gasses and even via poorly operated centrifuges. Water contamination and even salt contamination without the presence of water are very easy to detect either on board the vessel or in a laboratory.
Some months ago I was discussing the possible effects of water contamination with a colleague from Glacier who showed me the following rather dramatic example of just what can happen. His example was taken from a main engine thrust bearing. It is the partial remains of a large tilting thrust pad. We have all seen spare examples of these pads, greased up and bolted to racks on the bottom flat of many a ships engine room. They are not highly loaded and never seem to cause problems from one inspection to the next. This one did: and with a vengeance!
The lubricant in the thrust block had become contaminated with seawater. If fresh water is damaging, the addition of salts to the mixture greatly magnifies the effect. The type of corrosion in this example is not generally associated with fresh water contamination as it is electrochemical in nature. i.e. it requires an electrolyte and fresh water does not conduct very well, however, salt water fills this requirement admirably. The bearing overlay material is a tin based white metal alloy containing tin, copper and antimony in varying proportions.
The characteristic feature of salt-water corrosion in tin rich bearing materials is the formation of a hard black scale. This scale is not a deposit; rather it is formed from corrosion of the bearing metal itself. The scale has a lower density (greater volume) than the parent metal causing it to expand, fill bearing clearances, flake and spall off into the oil flow only to cause further damage downstream.
Does anyone wish to buy a ship - good condition, one owner, "minor" engine problems?
Some months ago I was discussing the possible effects of water contamination with a colleague from Glacier who showed me the following rather dramatic example of just what can happen. His example was taken from a main engine thrust bearing. It is the partial remains of a large tilting thrust pad. We have all seen spare examples of these pads, greased up and bolted to racks on the bottom flat of many a ships engine room. They are not highly loaded and never seem to cause problems from one inspection to the next. This one did: and with a vengeance!
The lubricant in the thrust block had become contaminated with seawater. If fresh water is damaging, the addition of salts to the mixture greatly magnifies the effect. The type of corrosion in this example is not generally associated with fresh water contamination as it is electrochemical in nature. i.e. it requires an electrolyte and fresh water does not conduct very well, however, salt water fills this requirement admirably. The bearing overlay material is a tin based white metal alloy containing tin, copper and antimony in varying proportions.
The characteristic feature of salt-water corrosion in tin rich bearing materials is the formation of a hard black scale. This scale is not a deposit; rather it is formed from corrosion of the bearing metal itself. The scale has a lower density (greater volume) than the parent metal causing it to expand, fill bearing clearances, flake and spall off into the oil flow only to cause further damage downstream.
Does anyone wish to buy a ship - good condition, one owner, "minor" engine problems?
