Water contamination in oil

All modern engine lubricants are designed to remain stable in the presence of small amounts of water. However, it is inevitable that at some time water contamination will adversely affect the operating performance of the lubricant. In extreme cases this may even result in complete failure of the engine.

Water contamination cannot realistically be avoided, although its effects can be limited by good maintenance policies. Water can enter the oil by various means: as a result of condensation, leaking coolers and deck vents, blow-by gasses and even via poorly operated centrifuges.

Both water contamination and even salt contamination without the presence of water are very easy to detect in the engine lubricant, by regular, routine sampling and testing either on board the vessel or through laboratory

services.

A dramatic example of the possible effects of water contamination can be seen with the main engine thrust bearing shown (below). Spare thrust pads, greased up and bolted to racks on the bottom flat are a common sight in many ships engine rooms. The photograph shows the partial remains of such a large tilting thrust pad. Generally these pads are not highly loaded and seem to cause few if any problems from one inspection to the next. In this case however, a catastrophic failure occurred.

Seawater

The lubricant in the thrust block had become contaminated with seawater. If fresh water is damaging, the addition of salts to the mixture dramatically increases the corrosive effect. The type of corrosion illustrated in this example is not generally associated with fresh water contamination as it is electrochemical in nature i.e. such corrosion requires an electrolyte. Fresh water is not a good conductor, but salt-water fills this requirement admirably.

The bearing overlay material

comprises 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 firstly expand, then to fill bearing clearances, flake and then spall off into the oil flow, only to cause further damage downstream. This hard scale will also score any metal surface that it contacts.

The blackened and scaled

appearance of the bearing illustrates the symptoms classically. The steel thrust collar of this bearing was found to be in a similar condition and the failure was terminal.

A simple testing regime could not have prevented water ingress, but it would have provided an early indication of water contamination. This would enable fast and effective remedial action to be taken before such damage occurred.

Test equipment

The type of equipment required to conduct such testing would, for

example, include the DIGI Test cell. Designed to analyse multiple oil breakdown characteristics, the dual purpose DIGI Test cell can measure both ?Water in Oil? and ?Total Base Number? (TBN) in one unit. This device provides a fast and accurate digital measurement for each parameter, allowing the engineer to effectively monitor and manage the condition of the oil and the equipment in which it is used.

A practical piece of equipment designed for marine use, the DIGI Test cell is machined from a tough

aluminium casing to withstand the rigours of daily use onboard. The cell has non-slip twist grips to ensure that it can be fully sealed when in use and includes a clear, scratch resistant LED display and touch pad controls.

Pre-programmed software built into the cell takes the user through a step-by-step process to analyse the oil sample and deliver an instant result.

Another useful test would be the ECON Salt Water Determination test. This simple and economic test enables the engineer to determine whether the water contamination is either fresh water or salt water, which in turn will help to establish exactly where in the system the water contamination

is occurring.

Together this equipment provides an ideal introduction to regular oil

sampling and testing. It can be used by the crew to monitor the lubrication of a range of onboard machinery,

consequently saving unnecessary equipment downtime, avoiding costly repairs and ensuring the consistent measurement, monitoring and management of their machinery lubrication

systems.