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Under the microscope

How new marine lubricants are put to the test

On any vessel, seals are exposed to extremely demanding conditions. To ensure they last, it is vital that they are lubricated with the right oil. However, before an oil is approved for use, it must be subjected to thorough testing.

Almost anyone could tell you that there are many different types of oil. But the range of marine lubricants on the market is surprisingly diverse—new products are launched virtually every month. These vary in certain aspects, such as their physical properties, durability, compatibility with other materials, and viscosity.



The USA leading the way

The current trend points towards environmentally acceptable lubricants (EALs). Since 2013, vessels operating within three nautical miles of U.S. coastlines and in the Great Lakes are required to use biodegradable lubricants in all oil-to-sea interfaces, such as sterntubes. This is stated in the Vessel General Permit from the US Environmental Protection Agency. And it is highly likely that other nations will soon follow suit and introduce stricter requirements. 

While a new oil may seem to have excellent properties on paper, what happens if, after months of use, the material of the sterntube seal suddenly becomes porous or warped? What if water seeps in or oil leaks into the ocean? Considering the increasingly strict environmental regulations, this could become very costly.

A list of approval

That is why SKF maintains a list of all lubricants that it has officially approved for use with its Simplex seals. Making it onto this list can play a major part in the commercial success of an oil. Therefore, oil producers and shipping companies apply for tests approximately three times a month. Oils need to pass this test before they can be added to the list.

The two-stage test process

First, in what is known as a static test, the various elastomers used in Simplex components are placed in a container with the oil. The duration of storage and the temperature are varied so the lubricant can be examined under all realistic conditions. After the elastomer is removed, SKF material testers check whether it has changed physically. For the oil to be approved, its physical properties must meet defined criteria and limits. But first, it must pass a second stage of testing.

Most organizations only conduct laboratory testing, which alone is not enough to detect everything. This is why a second phase is recommended.  Ideally, pure oil would be used for testing—but this rarely happens in practice. Therefore, SKF uses a mix of oil and water for the next test. At a defined and constant water content, the oil’s properties deteriorate. Only when this test is passed can the oil be approved.

EALs—more extensive tests for more complex products

The two-stage static test is also used for environmentally friendly oils. However, this alone is not enough. Some EALs begin to emulsify with water over time, and the thickened liquid can block pipes. In a demulsification test, testers prepare an oil-water solution and examine how quickly, and to what extent, the substances separate. Once this test has been passed, there is one final hurdle: the dynamic test. Using a full replica of a sterntube seal, the oil is examined for a longer period of time under real-life conditions.

The wide range of lubricants on the market can make it difficult for ship operators to make a decision. But with an approved oil, owners can rest easy knowing they have a product they can rely on in the long term.

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