I was recently assisting a plant evaluate their lubricant storage practices. During this trip, I was brought to four drums of the same type of oil. These drums were all stored vertically on a pallet with absolutely no protection from the elements. Dirt and water was pooled on top, and many of the labels had been bleached almost illegible from continuous exposure to sunlight. Only one of these drums had been opened. Upon further inspection we realized that the opened drum was six months old, and the oldest unopened drum was over five years old.
When I pointed out that one of the drums of “new” oil had been sitting there for over five years, the person I was with didn’t understand why this was a problem. “Oil is millions of years old.” they said, “How can 5 years in storage do any damage?” We then examined the drum for a “use by” date and quickly discovered it didn’t have one. This left a big question; how long can oil be stored?
While searching for an answer, I found many conflicting opinions. One thing was consistent; oil does indeed have a shelf life. This shelf life will depend on many factors, the top one being the conditions in which the lubricant is stored.
Outdoor storage of oil drums will contribute to the contamination and degradation of the oil. A sealed drum of oil will still expel and pull in air as the temperature within the drum changes. If water and dirt is allowed to collect on top of the drum, the water and dirt will enter the drum during this venting process.
Gradual ingression of dirt and moisture will have a cumulative effect on the quality of the lubricant. Water content will increase the rate of oxidation and can react with certain additives to form sludge. Exposure to the sun will increase the oil’s temperature, also increasing the rate of oxidation (for every 18°F increase in temperature, the oxidation rate doubles, cutting the usable life of oil in half). The longer the drum is exposed to these conditions, the greater the damage done.
Improving the storage practices will reduce the exposure to contaminants, but extended storage, even in the best conditions, will degrade the quality of lubricant. One of the biggest concerns with long term oil storage is the separation of additives.
Additives are added to base oils to improve the performance of the lubricant. Specific purposes of various lubricant additives are to reduce friction and wear, prevent corrosion, improve oxidation resistance, and stabilize a lubricant’s viscosity over wide range of temperatures. However some additives, such as sulfur, are insoluble to oil. Excessive storage can result in the additives separating, thus rendering the additive unusable. If this occurs, the lubricant may not function properly.
Shelf Life Estimates
The usable shelf life of a lubricant is greatly dependent on the type of lubricant, the method in which it is stored, and the container size it is purchased in. Lubricant manufacturers have differing opinions on how long a lubricant can be safely stored.
Shelf Life & Container Type
ExxonMobil estimates that their oils will last up to 10 years in storage, while their greases will last anywhere from 2 to 6 years. However, the life expectancy of oil changes based on the type of container it is stored in. Oils stored in quart containers have an estimated shelf life of 10 years, while drums only have a 5 year shelf life. Quarts will last longer in storage for two main reasons; plastic containers do not promote oxidation (as do steel drums) and quarts will typically be properly sealed, so they will not be exposed to outside contaminants during storage.
Source: “Aviation Lubricant Shelf Life.” 2015 Exxon Mobil Corporation
Confirm Oil Condition with Analysis
Lubricant manufacturers are adamant that their estimates on shelf life are not absolute, but rather a guideline. Once their estimated shelf lives are reached, it’s suggested that a user should utilize oil analysis to validate if the lubricant is suitable for use.
- Make sure you pay attention to the length of time a lubricant is allowed to sit before being used. Document the date you received and opened any lubricants.
- Try to cycle inventory to use the oldest material first and purchase lubricants in a quantity that will be used in a timely fashion.
- Improve the storage practices of your lubricants. Moving to indoor storage in a climate controlled area will greatly reduce the degradation of your oils and greases.
- If you must store oils outside, do so in a way that prevents water and dirt from freely collecting and entering the bungs.
To learn more about proper storage and handling techniques, take advantage of online resources. The links below are organizations that are dedicated to lubrication fundamentals and best practice:
http://www.lubecouncil.org/ - ICML (International Council for Machinery Lubrication) offers training and certifications for a wide range of lubricating topics.
www.machinerylubrication.com - Noria’s online publication focusing on current best practice. They also offer training courses relevant to lubrication fundamentals.
www.reliabilityweb.com – This online resource offers articles, videos and tips on everything from asset management to condition monitoring.