Page 217 - Intro Predictive Maintenance

208 An Introduction to Predictive Maintenance

with the objective of detecting large particles should be chosen. In a recirculating
system, samples should be drawn as the lubricant returns to the reservoir and before
any filtration occurs. Do not draw oil from the bottom of a sump where large quanti-
ties of material build up over time. Return lines are preferable to reservoir as the
sample source, but good reservoir samples can be obtained if careful, consistent prac-
tices are used. Even equipment with high levels of filtration can be effectively mon-
itored as long as samples are drawn before oil enters the filters. Sampling techniques
involve taking samples under uniform operating conditions. Samples should not be
taken more than 30 minutes after the equipment has been shut down.

Sample frequency is a function of the mean time to failure from the onset of an abnor-
mal wear mode to catastrophic failure. For machines in critical service, sampling every
25 hours of operation is appropriate; however, for most industrial equipment in con-
tinuous service, monthly sampling is adequate. The exception to monthly sampling is
machines with extreme loads. In this instance, weekly sampling is recommended.

Understanding the meaning of analysis results is perhaps the most serious limiting
factor. Results are usually expressed in terms that are totally foreign to plant engi-
neers or technicians. Therefore, it is difficult for them to understand the true meaning
of results, in terms of oil or machine condition. A good background in quantitative
and qualitative chemistry is beneficial. At a minimum, plant staff will require train-
ing in basic chemistry and specific instruction on interpreting tribology results.

9.2 SETTING UPAN EFFECTIVE PROGRAM
Many plants have implemented oil analysis programs to better manage their equip-
ment and lubricant assets. Although some have received only marginal benefits, a few
have reported substantial savings, cost reductions, and increased productivity. Success
in an oil analysis program requires a dedicated commitment to understanding the
equipment design, the lubricant, the operating environment, and the relationship
between test results and the actions to be performed.

In North America, millions of dollars have been invested in oil analysis programs with
little or no financial return. The analyses performed by original equipment manufac-
turers or lubricant manufacturers are often termed as “free.” In many of these cases,
the results from the testing have little or no effect on the maintenance, planning, and/or
evaluated equipment’s condition. The reason is not because this service is free, or the
ability of the laboratory, or the effort of the lubricant supplier to provide value-added
service. The reason is a lack of knowledge—a failure to understand the value lost
when a sample is not representative of the system, and the inability to turn equipment
and lubricant data into useful information that guides maintenance activities.

More important is the failure to understand the true requirements and operating char-
acteristics of the equipment. This dilemma is not restricted to the companies receiv-
ing “free” analysis. In many cases, unsuccessful or ineffective oil analysis programs
are in the same predicament. Conflicting information from equipment suppliers,