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A Baker's Analogy: Why Top-Treating Wind Turbine Oils with Additives Won't Deliver Optimal Performance

By Gary Hennigan, ExxonMobil

Over the years, much has been written about lubricant formulation and its impact on in-service performance.

Recently, however, there has been increasing talk about another lubricant performance strategy—top-treating wind turbine gearbox oils with additives to mitigate lubricant degradation and extend oil life.

But relying on additive top-treating as part of your primary lubrication strategy is not a recommended long-term solution, as it may introduce potential complications.

Instead, the key to long-term lubrication performance is to select an oil that is formulated with the right mix of advanced base oils and additives to deliver the required performance over many years, without the need for additive top-treating.

To better understand why formulation tops additive top-treating, consider a baking analogy.

If you want to bake the best cake possible, you need to follow two simple guidelines: use high quality ingredients, and ensure that all the needed ingredients are included in the cake mix before it is baked.

When it comes to the ingredients themselves, you'll be able to taste their quality in the final product—and poor quality ingredients will not result in a tasty cake.

Similarly, once the cake is baked, you cannot go back and add ingredients without further ruining the cake. Say, for example, that you forgot to include vanilla extract. Trying to add vanilla flavoring to an already baked cake would not be possible, and even if you tried to douse the cake in extract, it would result in an uneven distribution of flavor.

These same principles apply to an oil's formulation. Inserting additives once the oil is already in service isn't the same as using an oil formulated with the right "ingredients" to begin with. In fact, it could lead to greater challenges.

Let's start with a quick overview of additive top-treating.

With this approach, operators use condition monitoring to identify when an oil's additives start to deplete and then re-additize that oil with the addition of after-market additive packages.

While all oils will eventually start to deplete additives when in service, relying on top-treating to extend oil life is not a recommended best practice, as expressed in the baking analogy above.

For example, additive top-treating may actually introduce new components, or contaminants, that could impact the performance of your wind turbine equipment by generating an unbalanced formulation.

Surface active additives like anti-wear additives and rust inhibitors both compete for space on the metal surfaces in a gear box. Formulating an oil so that both of these types of additives are present in the correct amounts, to properly protect the machine elements from both wear and rust, is a delicate balance. Topping up with different ratios or different types of these additives could disturb the balance, creating more potential harm than good.


Further, top-treating oils with additives increases how often you have to interact with your equipment. While top-treating may not be as invasive as flushing and replacing an oil, regular additive top-treating requires more frequent equipment interaction, which in turn increases the potential for safety issues.

Instead of relying on additive top-treating to extend lubricant life, prudent operators should focus on selecting an oil that is formulated with the right mix of advanced base oils and additives to deliver long-lasting performance, without the need for additional additive top-treatment.

The best formulated oils will last longer—in some cases years longer—than poorly formulated oils, resulting in less frequent interaction with equipment and minimized risk of accidentally introducing insoluble contaminants into your lubricants.

The following spider chart compares the performance of various wind turbine gearbox oils. The red line represents the performance characteristics of a high quality synthetic oil that has a balanced formulation. You can see that this oil delivers significant performance benefits over other oil formulations, particularly for key areas such as oxidative stability and filterability, while maintaining a balanced overall performance profile.

As you can see, the best formulated lubricant can deliver exceptional performance and test results show how it has the potential to better withstand degradation than oils with a less robust formulation. That's why lubricant companies that understand the importance of an oil's initial formulation stand behind their products. For example, some of ExxonMobil's synthetic wind turbine oils are warrantied for up to seven years, demonstrating the capability for the fluid to protect the machine even after 60,000 hours in service.

When it comes to wind turbine equipment, the first—and most important—consideration should be lubricant formulation to make sure your equipment will be better protected in the long run, and that you won't need to take risks with additive top-treating.

To learn more, check with your lubricant supplier to ensure you are using the right oils for your equipment.

Gary Hennigan is a national account sales executive, supporting the wind, cement, and food processing industries for ExxonMobil Fuels & Lubricants. With more than 18 years of experience in the lubricants industry, Gary has held a variety of sales and marketing positions with ExxonMobil.