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Lubricant Storage Life Limits - Industry Needs a Standard
Drew Troyer and Jenny Kucera
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These days, anything you buy seems to have anexpiration date. You’ll find a “Best if Used By” label on everything from milk to batteries, but you won’t find such a date on greases and oils.
What is the acceptable storage life for a pail of Lithium Complex EP grease, or a drum of R&O 32 Turbine Oil? What difference does the storage environment make? What should you do to guard against storing a lubricant beyond its usable date? What tests should beconducted before using a lubricant that has been stored too long? The answers to these questions are important to achieving lubrication excellence. The editorial staff of Machinery Lubrication magazine polled several lubricant suppliers, large and small, to see what they had to say about the issue of lubricant storage life limits, then reviewed the literature on the subject in efforts to report aconsensus best practice. We found that the stored lubricants degrade for a number of reasons, which are summarized in Table 1. Oxidation occurs in all oils that are in contact with air, including stored lubricants. The base oil and additive combination affects the rate of oxidation, and the presence of the thickener in grease can increase the degradation rate. But the environmental and storageconditions have the greatest influence on the rate at which the lubricant degrades. Increasing the temperature at which the lubricant is stored by 10°C (18°F) doubles the oxidation rate, which cuts the usable life of the oil in half. The presence of water, usually introduced as a result of temperature variations, increases the rate of oxidation. Frequent agitation of the lubricant incorporates airinto the oil. This increases the
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Machinery Lubrication Magazine
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surface area contact between air and the oil, increasing the rate of oxidation. Agitation also serves to emulsify water into the oil, increasing its catalyticeffect on the oxidation process. The storage container itself can affect the rate of oxidation. A poorly prepared steel drum can expose the oil to iron, which catalyzes the oxidation process. Of course, the use of nonreactive (plastic) containers or drum liners eliminates the metal catalyst affect on oxidation. Lubrication book authors George Wills and Dr. A.R. Landsdown suggest that inventory levelsbe set so that lubricants are used within 3 to 12 months, depending upon the lubricant type (Table 2 below). Set inventory levels to stay within targets. If limits are reached, verify quality with oil analysis. Little is said with respect to influence of environment.
Lithium Greases Calcium Complex Greases Lubricating Oils Emulsion Type Fire-Resistant Fluids Soluble Oils Custom BlendedSoluble Oils Wax Emulsions
Maximum Recommended Storage Time
12 months 6 months 12 months 6 months 6 months 3 months 6 months
Table 2. Wills’ Recommended Shelf Life for Select Lubricants The ML editorial staff polled several lubricant suppliers, ranging from large multinational corporations to small independent suppliers, and lubrication consultants to get their recommendations forlubricant storage life. We asked them to recommend storage life limits for numerous lubricant types, ranging from simple R&O 32 turbine oil to EP grease, under varying temperature and humidity conditions. We were attempting to identify a consensus of opinion, or at least a reasonable range, to share with ML readers as a best practice. We found a startling variation in responses and a concerning degree...