In addition to selecting the appropriate grease for the application, do not overlook the product’s shelf life. Shelf life represents the time period during which a stored product can continue to be used without quality-control checks to verify performance attributes.
Shelf life is provided as guidance and applies to lubricants that have been stored in their original sealed containers under proper conditions, say officials with ExxonMobil, one of the world’s largest integrated refiners, marketers of petroleum products and chemical manufacturers (www.exxonmobil.com). In general, the recommended shelf life for oils and greases is typically five years.
At the end of the shelf life period, they recommend laboratory testing (recertification) to ensure that the product will continue to provide the promised performance in the intended application.
SIGNS OF DETERIORATION
The officials say greases may show deterioration in one or more of the following ways:
- Excessive oil separation. (Some “bleed” is normal and required.)
- Significant change (greater than 25 percent) in the grease consistency as measured by worked or unworked penetration.
- Significant change in color or odor.
SERVICE LIFE
“There is a fundamental difference between product life in storage and product life in service,” point out ExxonMobil officials.
“During storage, the packaged product generally remains motionless for extended periods and can be exposed to cyclic variation in temperature and other environmental conditions, such as vibration,” they explain. “This can impact the components of the formulation or potentially allow ingress of contaminants from the environment – both of which have the potential to affect the product’s performance characteristics.
“However, when the lubricant is in service, it is exposed to the dynamic conditions of the lubricated system (e.g., circulation, splashing, churning, etc.). Once a product has been placed in service, its suitability for continued use becomes a function of other factors.”
These factors include:
- The procedure for lubricant replacement.
- OEM recommendation for re-lubrication or change interval.
- Recommendations from a lubricant engineer.
- End-user company policy.
- Condition-monitoring information from equipment- and oil condition monitoring programs.
- Lubricant contamination with process materials, water, dust, wear debris, other lubricants, etc.
- The equipment for which the lubricant was originally recommended may have been replaced or modified.
- A better product may have been developed
“In each case,” counsel the officials, “the lubricant product should be evaluated both for quality and for suitability in the equipment in which it will be employed.”
