Efficient Plant September 2021 - 21

feature | lubrication solutions
Failure Mode Vibration
analysis
Looseness
Machine
resonance
Alignment
Unbalance
Fluid
analysis Comments
Strength Weakness
Strength Weakness
Strength Weakness
Strength Weakness
Structural looseness, incorrect tightening, and poor component fi t can all be detected through vibration analysis,
coupled with motion-amplifi cation techniques.
By looking at the amplitude and phase of vibration during start-up and slow down, resonance can be detected as a large
increase in amplitude as the machine transitions through the speed that corresponds to a natural resonance frequency
of the machine.
While the eff ects of long-term misalignment will be seen as an increase in internal wear due to the impact on internal
clearances, vibration analysis provides a very early indication of parallel and angular misalignment.
Like misalignment, vibration analysis is an early indicator of unbalance conditions, compared to oil analysis which will
only show the long-term eff ects of unbalanced rotors.
Wrong lubricant Weakness
Degraded
lubricant
Under/over
lubrication
Water
contamination
Particle
contamination
Active wear-
rolling element
bearings
Active wear-
journal bearings
Active wear-
gears
Greased
lubricated
bearings
Weakness
Strength
Weakness
Strength
Strength
Strength
Strength
Weakness
Strength
Depending on the time the wrong lubricant is in use, vibration may show evidence of loss of fi lm strength in the highfrequency
(>20 KHz) range. By comparing in-service oil samples with a new-oil reference sample, incorrect lubricant
usage can be detected through routine oil analysis as a change in viscosity and/or additive composition.
By comparing the physical and chemical properties of in-service oil samples with a new-oil reference, oil analysis can
provide a very early warning of lubricant degradation.
Incorrect oil level-particularly too little oil-can be detected as a loss of fi lm thickness through high-frequency
vibration analysis. While active machine wear due to incorrect oil level can be detected using oil analysis, under or
over lubrication is best detected through visual oil analysis (checking oil level in the sight glass), in conjunction with
thermographic analysis.
While loss of oil fi lm and subsequent bearing/gear wear due to water ingress can be observed using vibration analysis, oil
analysis can provide an early, proactive warning of moisture ingression, provided the correct test for water is used.
Particle contamination can lead to a multitude of wear modes, including three-body abrasion, erosion, and particleinduced
contact fatigue. Establishing proper target cleanliness levels and using oil analysis to monitor and control
particle contamination is a proactive strategy that mitigates the impact of particle contamination.
Strength
Strength
Vibration and oil analyses will pick up active rolling-element bearing wear. Provided samples are taken from the right
location, oil analysis will typically show a problem earlier while vibration analysis does a much better job of identifying
the source of the wear (inner race, outer race). The effi cacy of oil analysis is strongly influenced by sump capacity since a
large oil volume can dilute wear debris below detectable limits.
Strength Variable
While vibration analysis can detect certain problem conditions, such as oil whirl, leading to possible oil whip failure,
oil analysis is far better at detecting plain bearing wear from small amounts of wear debris formed due to two-body
abrasion (rubbing) from loss of hydrodynamic oil fi lm. Oil analysis is best suited to small- and medium-sized assets
versus large turbomachinery where proximity probes provide an earlier warning of oil instability.
Strength
Strength
While oil analysis and vibration analysis will both detect gear wear, some failure modes, such as broken or cracked gear
teeth, are best detected with vibration analysis. Other failure modes usually show up fi rst in oil analysis. Typically, oil
analysis is the earliest indicator while vibration analysis provides far greater localization/specifi city of the nature of the
failure.
Strength
Strength
Issues such as under and over lubrication can be detected through high-frequency vibration analysis, as well as
ultrasound. Periodic analysis of in-service grease can be used to trend grease degradation rates and contamination
issues. Grease and vibration analyses will show signs of active wear, though vibration analysis will provide better
localization of the problem.
Including vibration and fluid analyses in your condition-monitoring program will provide vital predictive and proactive data sources.
approach-two of the more tried and
trusted methods for rotating equipment are
vibration and oil analysis. In the hands of a
trained, skilled practitioner, these two methods
serve as vital predictive (aſt er a failure
has started) and proactive (prior to failure
initiation) data sources. Which one is better?
Should you invest time, eff ort, and money in
one versus the other? Th e answer is both.
SEPTEMBER 2021
Th e table provides a critical look at the
benefi ts and effi cacy of vibration analysis
and fl uid analysis when addressing common
rotating failure modes. In the past 20 years,
several tools, technologies, and strategies
have merged, all focused on increasing asset
reliability. Two of the oldest-oil analysis
and vibration analysis-are still as relevant
today as they were when they were fi rst
invented. When combined, they off er a comprehensive
and unparalleled source of data
to drive condition-based decisions. EP
Mark Barnes, CMRP, is Senior Vice President
at Des-Case Corp., Goodlettsville, TN
(descase.com). He has 21 years of experience
in lubrication management, oil analysis, and
contamination control.
EFFICIENTPLANTMAG.COM | 21

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Efficient Plant September 2021

Table of Contents for the Digital Edition of Efficient Plant September 2021