To better understand the aviation industry’s key concerns and pain points related to grease storage, handling, and application best practices, ExxonMobil asked MRO Americas attendees to submit their grease-related questions directly to the ExxonMobil team. Having collected more than 40 questions on topics, including color, formulation, storage, and handling, ExxonMobil has offered to share the answers in a three-part series.
Gary Dudley, Ph.D., Global Grease Product Technical Advisor for ExxonMobil Research & Engineering Lubricants Technology, tackles the below questions on grease shelf life and storage best practices.
Q. Where and how should you store greases?
Grease containers should be stored indoors in dry, cool, and clean environments. Normal storage temperatures should range from 0 C to 40 C (32 F to 104 F). In the event that a stored grease is briefly exposed to severe temperatures or environmental conditions, technicians should consult their suppliers with concerns.
Once a container is opened, the grease should be used as soon as possible to avoid potential contamination or degradation.
Since the rate of grease degradation can be impacted by exposure to contamination and/or storage and handling conditions, the listed shelf life recommendation for a grease is no longer applicable once the container is opened.
For more information on storage and handling best practices, review our technical topic here.
Q. How long does grease actually last?
Shelf life specifications can differ between aviation greases. Typically, aviation grease shelf life is listed as the “use by” date on the container.
The average industry shelf life of aviation greases is about three years, however, ExxonMobil’s Mobilgrease™ 33 and Mobilgrease™ 28 aviation greases offer extended shelf life for up to 10 years.
Q. Why can't you use grease after its expiration date?
While it’s dependent on the product’s history, it’s likely an expired grease has degraded. Using a grease past its expiration date also exposes a user to other risks associated with using an unapproved product.
The shelf life of grease is really a measure of the useful life of the components in the grease to ensure it is still fit for use. As the product exceeds its shelf life, a decrease in the performance additives that provide wear protection, oxidation stability, and grease structural stability may be observed.
As mentioned previously, to maximize shelf life, normal storage temperatures should range from 0 C to 40 C (32 F to 104 F), and containers should be kept indoors in a clean and dry environment. This helps avoid hydrolysis and other environmental factors that may impact the storage life of the product.
Q. Why do some greases have a longer shelf life than others?
While all aviation greases comply with the same specifications, they do differ in their formulations, chemistry, and performance properties. As a result, the shelf life can vary from one supply to the next.
If the grease is not stored properly, it’s also more likely to accelerate deterioration before the expiration date and may no longer be used on an aircraft.
Q. Can grease be recertified to extend the shelf life? Is there any risk?
Although the FAA can approve recertification, the process involves lengthy and rigorous testing, which is conducted by the grease manufacturer. Applying a recertified grease is risk-free. The FAA would not reapprove or recertify a grease if there was an issue with the product.
Coming up in AMT’s October issue, Part 2 will focus largely on grease compatibility, conversions, and contamination.
