Maintenance Technology August 2016 - (Page 38)
Practical Oil Analysis:
Why and What For?
Simply hoping your lubricants are operating
within their protective-specification
limits doesn't make it so.
LUBRICANTS ARE DESIGNED and chosen to perform as finite
and perishable, integral components of host machines. Rarely,
if ever, will a lubricant be employed in identical application and
environmental conditions. Enter oil-analysis testing.
Why we test
The uniqueness of lubricants reflects how and when they must
be tested, maintained (filtered and temperature controlled), and
changed out. Stresses and influences such as load-induced shear
stress, thermal degradation, various types of contamination, and
wear-metal-catalyzing alter and prematurely degrade lubricant
Oil is made up of a base oil and an additive package that's
designed to combat ambient and working environmental stresses/
influences and deliver reasonable lubricant life. Outside stresses
produce an array of detrimental effects, including oxidation,
polymerization, cracking hydrolysis, and evaporation that manifest
as thickening or dilution of viscosity, acid buildup, and sludge.
Additionally, when oil loses some of its protective ability, its host
bearings can come into contact with one another and release
metal-wear particles into the lubricant, which then act as a bearingattacking abrasive material (three-body abrasion).
These effects and conditions are why we analyze oil. This testing
is how we ensure lubricants are serviceable and bearing surfaces
What we test for
Oil analysis is analogous to a blood test wherein a single, properly
extracted fluid sample is used for a variety of diagnostics that
indicate machine and lubricant conditions. To ensure an accurate
interpretation of results every time-reliable ones suitable for
trending and historical analysis-samples must be collected in a
consistent manner and sent to the same laboratory for testing on
the same equipment.
The lab will also require a virgin sample of any lubricant to be
tested. This sample is used to document baseline measurements
of base-oil type, additive-package levels (metals and chemicals),
cleanliness level (dirt-contamination level), and viscosity and
acidity. A set of initial samples detailing how and where each was
taken will also be required for each machine.
Good laboratories also document an operational profile for
each machine tested. Based on it, they can recommend additional
beneficial testing, e.g., a Karl Fischer water-contamination test for
MEch Eng (UK)
Standard Elements Tested by Oil Analysis
The table shows elements that are tested in a standard
oil analysis. To establish a baseline, labs require a virgin
sample of any lubricant to be tested.
a food plant with daily machine wash downs; tests for soot and
glycol in mobile equipment and generator engines; or ferrographic
analysis of metal particulates to determine specifically how a
bearing is failing.
Basic oil analysis concentrates primarily on fluid property and
In analyzing fluid properties, laboratories typically look at viscosity,
acidity, and additive elements-the "big three" characteristics that
make oils unique-and which, through their changes in service,
can tell us how to better maintain our lubricants.
Viscosity. The viscosity rating of new oil is typically measured in
centistokes (cSt), i.e., oil's kinematic viscosity depicting measured
resistance to flow and shear by the force of gravity. As oil thickens
or dilutes over time, however, its specific gravity changes, leading
to errors in gravity-based tests. A more consistent measurement is
achieved by checking for the absolute viscosity rating depicting oil's
resistance to flow and shear through measurement of its internal
friction. Because absolute viscosity is measured by multiplying
kinematic viscosity by the actual specific gravity, it's an accurate,
error-free trending method of choice for most laboratories. To
understand which tests your lab used, note the measurement
Table of Contents for the Digital Edition of Maintenance Technology August 2016
On The Floor
Accepting The Challenge
Advanced Software In The Jungle
Put Efficiency in MRO Storerooms
Rethink Overall Vibration Monitoring
Reliable Pumping Supplement
Practical Oil Analysis: Why and What For?
SAP Tips and Tricks
Compressed Air Care
Nurture STEM Learning
Heed Drive-Belt Temps
Internet of Things
Maintenance Technology August 2016