pwr_april-2024 - 15

FOCUS ON O&M
2. The Membrane Patch Colorimetry test is used to measure the color bodies of insoluble contaminants
in lubricants. By monitoring the level of insolubles present in the lube oil, informed
decisions can be made regarding the implementation of varnish mitigation technology. Courtesy:
Eurofins TestOil
Vessel Oxidation Test (RPVOT) is a test
that determines the oxidation stability
of an oil. RPVOT measures the actual
resistance to oil oxidation, whereas, the
other tests detect oxidation that is already
present in the oil. Oxidation is a
critical mode of lubricant degradation.
As oil oxidizes it forms acids and insoluble
oxidation products, which can lead
to formation of sludge or varnish. These
degradation products can coat bearing
and oil cooler surfaces, preventing adequate
cooling of the bearings. Areas
with tight tolerances such as hydraulic
control valves can also become coated
causing operational issues.
Ruler; ASTM D6971. Linear sweep
voltammetry, more commonly referred
to as the Remaining Useful Life Evaluation
Routine (RULER) test, measures
hindered phenolic and aromatic amine
antioxidant content. This test quantitatively
analyzes the relative concentrations
of antioxidants in new and used oils
in order to monitor the depletion rates
of the antioxidant protection package in
the oil. Hindered phenols and aromatic
amines are primary antioxidants used in
many industrial oil and zinc-free turbine
oil applications. By measuring the depletion
and available reactivity of these antioxidant
compounds while conducting
other routine performance tests, the service
life of used lubricants can be effectively
monitored. The level of antioxidants
present in the lubricating oil gives an indication
of the ability of the fluid to resist
oxidation. Regular monitoring allows the
rate of depletion to be observed and can
be useful in determining remaining useful
life so that informed decisions can be
made regarding oil changes.
April 2024 | POWER
Rust A; ASTM D665 procedure A.
The Rust Preventing Characteristics Test
(ASTM D665) is designed to measure
the ability of industrial oils to prevent
rusting under conditions of water contamination.
The test can be performed
with either distilled water or synthetic
seawater. The test consists of stirring a
mixture of 300 milliliters of the oil being
tested with 30 milliliters of water, either
distilled or seawater, at 140F (60C) for
four hours. A special cylindrical steel test
specimen made of #1018 cold-finished
carbon steel is polished and then completely
immersed in the test fluid. At
the end of the four-hour test period, the
specimen is removed, washed with solvent,
and rated for rust. A lubricant's ability
to prevent rust is crucial for systems
that have significant risk of water contamination.
Testing a lubricant to determine
if it has the capabilities to protect
against rust is vital for maintaining the
health of ferrous components within the
equipment. In addition, rust particles can
act as oxidation catalysts and can cause
abrasive wear in journal bearings.
Spectroscopic Analysis; ASTM D5185.
The Elemental Spectroscopy test uses
a spectrometer to measure the levels of
specific chemical elements present in an
oil. Monitoring the concentration of metallic
elements can provide important information
regarding machine and lubricant
condition. By monitoring wear metals
such as iron, copper, tin, and lead, rates of
wear can be observed and abnormal wear
modes can be detected. Many contaminants
have metallic components that can
be monitored as well. Increases in contaminant
metals such as silicon, aluminum,
and potassium can indicate ingression of
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dirt, coolant, or process contaminants.
Some additives also have metallic components.
Monitoring additive metals can help
indicate when a system has been topped
off with the incorrect lubricant.
Viscosity; ASTM D445. The single
most important property of a lubricant is
its viscosity. It is the measure of the oil's
resistance to flow (shear stress) under
certain conditions. It is an important criterion
in the selection of a fluid. At low temperature,
excessive viscosity may result
in poor mechanical efficiency, difficulty
in starting, and wear. As oil temperature
increases, viscosity decreases, resulting
in lower volumetric efficiency, overheating,
and wear. Selection of the optimum
fluid viscosity grade will provide the most
efficient machine performance at standard
operating temperatures, therefore
minimizing lost time, and energy and fuel
costs for the operator.
Understanding Results
The resulting annual turbine analysis
report should be a complete rundown of
each of the tests performed, along with
a detailed explanation of each test result.
The report should also contain a summary
of findings, as well as recommended
actions specified by analysts. Critical indicators
commonly uncovered in an annual
analysis include a failing foam test, a
failing demulsibility test, low RPVOT, and
high varnish potential.
Ideally,
turbine oils should also be
monitored monthly with routine oil analysis.
The test slate might include:
■ Acid number
■ Elemental spectroscopy
■ FTIR spectroscopy
■ Viscosity
■ Particle count
■ Water content
Inherent in the power generation industry
are distinct fluid challenges that
ultimately decide the operational reliability
of plant equipment. Whether the plant
is powered by fossil fuel, nuclear energy,
gas, hydro, or wind, turbine maintenance
requires expertise to determine the condition
of the turbine's fluid and overall
health. No turbine can perform optimally
with degraded oil. With regular testing,
that's one issue plant managers can take
off their plate. ■
-Mary Messuti is president of Eurofins
TestOil. The Strongsville, Ohio-based
company offers lubrication testing, as
well as fuel, coolant, grease, and
associated tribology services.
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