Online Test of Lube Oil Keeps Check on Water Content

By George Backwell at February 20, 2011 21:56
Filed Under: General

"Oil and water don't mix", was oftentimes muttered to explain a certain amount of tension between deck and engine-room personnel in days long past when low-tech ships were manned with far more crew than today.

However, the saying is not entirely true as far as lube oil is concerned, since it contains added chemical emulsifiers and detergent, allowing water to mix, or dissolve in this type of oil: only after saturation point is reached will water content indeed finally become separated and then the familiar saying becomes true. These additives to cylinder lube in slow-speed diesel engines are necessary to neutralize acidic products of combustion and also to keep metal surfaces clean.

The latest generation of marine diesel engines has higher firing pressures and better combustion characteristics to achieve thermal efficiency, fuel economy and reduced carbon emissions even when burning low-end bunkers, but  successful operation depends upon the quality of the lubricant. High moisture content, mostly stemming from the age of the lube, increases the risk of overheating, corrosion, and consequent expensive and time-consuming mechanical failures. Online monitoring helps avoid such pitfalls.

Measurement of Moisture in Lube Oil

Unlike traditional lube oil oil analysis, which meant a wait for sample test results, in-line sampling allows operators to have a continuous record of moisture in lube content, as well as the benefit of protective alarm systems to warn when critical saturation levels are becoming close.

Present-day electronic devices on the market allow continuous monitoring of lube by means of a probe, usually installed in a high-flow feed line, or in the return line to reservoir. One state-of-the-art probe consists of a capacitive-type sensor made up of upper and lower electrodes sandwiching an insulating dielectric which absorbs and desorbs water molecules in the oil flow, a process that changes the dielectric constant and thereby the capacitance of the sensor. Read-outs of moisture in oil content (and temperature) are then transmitted for display online, making the device a key component of any preventive maintenance program.

Lube Oil Monitoring by Sample: USN photo by Photographer's Mate Airman Patrick L. Heil

MAN Diesel & Turbo Acknowledge Benefits of Continuous Lube Oil Monitoring

Following a thorough testing program of a whole range of commercial water-in-oil sensors, innovative Finnish company Vaisala proudly reported on 31, January 2011 that its MMT330 moisture and temperature transmitter had been approved by major engine manufacturer MAN Diesel & Turbo for use in the lubricating oil system of its two-stroke marine diesel engine designs.
Senja Paasimaa, a regional marketing manager at Vaisala, summed up: "The engine is the heart of a ship. Ensuring its operation is a truly business-critical task."

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