The plant experience shows that the oil even after completion of a number of hours of recommended operation has some residual life. It is desirable to maximize its use to conserve this scarce resource but avoid failures. At present, continuation or change of the oil is decided, based on the manufacturer's recommendation and experience in the plant. The suggested oil change period is conservative and results in non‐efficient usage of oil. This practice needs refinement to include all possible properties/attributes of oil and use of appropriate procedure to assess its realistic performance degradation and determine the remaining useful life (RUL) of lube oil.
Analytic hierarchy process (AHP), a multi criteria decision‐making method, in conjunction with vector projection approach is applied to assess the remaining useful life of lube oil.
Physical and chemical properties related to degradation of the lube oil are considered as lubricant attributes and their weights for given application is assigned, using AHP. The value of these attributes from time to time, obtained by testing samples drawn from the system, are analyzed through vector projection approach. In this approach, module, cosine of angle and projection are defined and evaluated at different time intervals. The projection is related to module and cosine of angle and is related to RUL of the lubricant. The suggested procedure is illustrated by means of an example.
The suggested procedure will be helpful for the maintenance personnel in planned oil replacement, with maximum usage of the lube oil but avoiding failures.
