Shell: Lubes "Not Only About Matching BN to Sulfur Content"

Shell Marine Products says an imbalance between the acid stress a cylinder oil faces and its BN can lead to scuffing and cylinder liner damage

Shell Marine Products (SMP) says that selecting an effective lubricant for use with low-sulfur fuels, now a more common practice with the existence of Emission Control Areas (ECAs), is not only about matching base number (BN) to the fuel's sulfur content, Marine Link reports.

"It is not only about matching BN to sulphur content. Our intensive research has shown that, in addition to acid stress, the cylinder oil in low-speed, two-stroke engines is exposed to thermal, insolubles and humidity stress,"\u00a0says Jan Toschka, General Manager at SMP.

"An imbalance between the acid stress a cylinder oil faces and its BN can lead to excessive deposits on piston top lands, rings, and ring grooves, leading to scuffing and cylinder liner damage. This means higher maintenance costs and reduced vessel availability."

The BN of a lubricant is the milligrams of Potassium Hydroxide per gram of oil (mg KOH/g), a measure of the alkalinity available to neutralise the sulfurous, acidic by-products of combustion.

For traditional fuels, with a sulfur content of up to 3.5 percent, manufacturers recommend 70BN or 100BN lubes, while low sulfur ECA lubes have called for 40BN or lower lubes.

This is because that while the BN of a lube needs to be high enough to neutralise the acid produced during combustion - a "shortage" of alkalinity can lead to excessive corrosion by the un-neutralised acid - an excess of un-depleted base can form hard deposits leading to wear.

In September 2014, SMP launched 25BN Shell Alexia S3 (SAE50), formulated for use with low-sulfur and distillate fuels up to 0.5 percent sulphur content, and in April said it has been "pleasantly surprised" by demand for the product.

Last year Iain White, field marketing manager at ExxonMobil Marine Fuels & Lubricants, talked to Ship & Bunker to explain the history behind cold corrosion.



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