In most maintenance organizations, lubricants are classified as consumables: purchased, stored, issued, used, and periodically replaced. It can, however, understate the lubricant’s role in equipment reliability. A more useful maintenance perspective treats lubricant as having a dual identity: a consumable whose quantity is depleted and a maintainable, functionally repairable machine component.
Lubricant consumption is unavoidable. Oil is progressively lost through leakage, evaporation, combustion, and other operating conditions, requiring replenishment. Consumption can therefore be forecast from operating conditions and managed alongside maintenance spares[1] .
However, like a repairable component, lubricant condition deteriorates during service. Oxidation, contamination, additive depletion, viscosity changes, and wear-particle accumulation gradually reduce its ability to perform its intended function. Unlike a conventional consumable that is simply discarded, lubricant condition can be monitored and interventions selected according to its actual state.
These interventions include full-volume or partial oil changes, filtration, centrifuging, accessory changes, and system purging [1]. A full-volume change drains and replaces the entire lubricant charge, when significant oxidation, viscosity change, additive depletion, or contamination has occurred. It restores the lubricant to a baseline but costs more and generates more waste.
A partial oil change replaces only part of the charge, leaving the remainder in service. Where contamination is moderate, this can dilute contaminants and replenish additives without the cost and waste associated with a complete change. It can be useful in large-volume systems such as turbines and hydraulic reservoirs, sometimes between scheduled full changes.
Filtration and centrifuging provide another form of lubricant “repair” by removing contaminants, water, and wear debris while retaining usable oil. Where appropriate, filtered used oil with low metal and water content may also be reused for less-sensitive applications. Reuse decisions must consider the application and oil condition rather than assuming that filtered used oil remains suitable.
Re-refining extends the concept further by treating used oil as a valuable core for recovery. Used oil is collected, dehydrated and separated through processes such as vacuum distillation, then further purified through hydrotreatment. The recovered base oil can subsequently be blended with additives to produce lubricants. In this sense, re-refining resembles liquid remanufacturing, extending the useful life and value of the lubricant’s hydrocarbon base.
The maintenance implication is significant: lubricant should not automatically be replaced simply because it has reached a predetermined interval. Condition monitoring can establish whether oil remains serviceable, requires filtration or partial replenishment, or has reached a condition requiring complete replacement.
The question, therefore, is not whether lubricant is a spare or consumable, but how it should be managed as a machine component whose quantity is consumed, condition deteriorates, and function can sometimes be restored. This approach can reduce unnecessary oil changes, support equipment reliability, control waste, and integrate lubrication effectively into asset-management strategy. .
Reference
[1] J. Wakiru, L. Pintelon, P. N. Muchiri, P. K. Chemweno, and S. Mburu, “Towards an innovative lubricant condition monitoring strategy for maintenance of ageing multi-unit systems,” Reliability Engineering & System Safety, vol. 204, p. 107200, 2020, doi: 10.1016/j.ress.2020.107200.
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SOURCE | SHUTTERSTOCK