pwr_april-2024 - 14

O&M
Critical Importance of
Annual Turbine Oil Analysis
Turbines are by far the single most-costly
piece of equipment for many energy
businesses, which highlights the importance
of lubrication for these assets.
Although turbine oil could last for more
than a decade, it can start degrading long
before that. Given this, and because oil is
the lifeblood of turbines, regular testing
is important.
Turbine oils, particularly those used in
steam turbines, are expected to last 10 to
20 years. While monthly oil analysis delivers
a basic view of the oil's condition,
there are additional tests that should be
performed to monitor key performance
characteristics of the oil and help prevent
unexpected downtime.
Annual monitoring of the oil's physical
and chemical properties, together with
common contaminants such as water and
solid particles, is essential for equipment
in the power generation sector (Figure
1). This thorough analysis is also recommended
for new oils that must meet rigorous
performance specifications prior to
selection and use in a new application.
Testing Lubricating Oils
The following tests/test methods should
be included in an annual turbine analysis
(Editor's note: ASTM International, formerly
known as American Society for
Testing and Materials, is an international
standards organization that develops and
publishes voluntary consensus technical
standards for a range of materials,
products, systems, and services. ISO
stands for the International Organization
for Standardization, an independent,
non-governmental international standard
development group.):
Acid Number; ASTM D974. Acid Number
(AN) is an indicator of oil serviceability.
It is useful in monitoring acid buildup
in oils due to depletion of antioxidants.
Oil oxidation causes acidic byproducts to
form. High acid levels can indicate excessive
oil oxidation or depletion of the oil
additives and can lead to corrosion of the
internal components. By monitoring the
acid level, the oil can be changed before
any damage occurs.
Color; ASTM D1500. The ASTM D1500
color scale is used for contamination
monitoring. If the fluid's color is off specification,
this can indicate contamination.
Demulsibility; ASTM D1401. Demulsibility
measures an oil's ability to release
water. Water-shedding characteristics
are important to lube oil systems that
have potential to have direct contact
with water. Demulsibility can be compromised
by excessive water contamination
or the presence of polar contaminants
and impurities.
Foam; ASTM D892. The tendency of
oils to foam can be a serious problem
in systems such as high-speed gearing,
high-volume pumping, and splash lubrication.
Inadequate lubrication, cavitation,
and loss of lubricant due to overflow can
lead to mechanical failure. This test evaluates
oils for such operating conditions.
Fourier-transform infrared (FTIR); Joint
Oil Analysis Program (JOAP) Method,
TestOil Turbine Method. Every compound
has a unique infrared signature.
FTIR spectroscopy monitors key signature
points of a specific lubricant in the
spectrum. These signatures are usually
common contaminants and degradation
byproducts unique for a particular lubricant.
Molecular analysis of lubricants and
hydraulic fluids by FTIR spectroscopy
produces direct information on molecular
species of interest, including additives,
fluid breakdown products, and external
contamination. It compares infrared spectra
of used oil to a baseline spectrum.
Karl Fischer Water; ASTM D6304
procedure C. Low levels of water (0.5%)
are typically the result of condensation.
Higher levels can indicate a source of
water ingress. Water can enter a system
through seals, breathers, hatches,
and fill caps. Internal leaks from heat
exchangers and water jackets are other
potential sources. When free water (nonemulsified)
is present in oil, it poses a
serious threat to the equipment. Water
is a very poor lubricant and promotes
rust and corrosion in the components.
Water in any form will cause accelerated
wear, increased friction, and high operating
temperatures. Non-emulsified water
poses a serious threat to the equipment,
leading to rust and corrosion. Emulsified
water will promote oil oxidation and reduce
its load handling ability.
Membrane Patch Colorimetry; ASTM
D7843. The Membrane Patch Colorimetry
test (Figure 2) 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, and costly downtime can be
avoided. Continued testing once varnish
mitigation has been implemented can be
used to help evaluate the effectiveness
of the technology in use.
Particle Count; ISO 4406. Using the
1. Annual monitoring of a lubricating oil's properties is essential to keep rotating equipment
performing at peak levels. Many types of equipment can benefit from this monitoring, including
diesel generators (shown here), turbines, hydraulic systems, gearboxes, pumps, and compressors.
Courtesy: Eurofins TestOil
14
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Pore Blockage method, the sample is
passed through a calibrated screen.
As particles collect on the screen, the
amount of flow decreases. This decrease
in flow is measured and the particle
count result is obtained. Higher levels of
particulates in the sample may indicate
machine health issues, a high rate of external
particulate ingression, or filter inefficiency.
High levels of particulates can
lead to accelerated machine wear due to
abrasive conditions. Maintaining lower
levels of particulates can increase the
operational life of lubricated equipment.
Rotating Pressure Oxidation;
ASTM D2272. The Rotating Pressure
POWER | April 2024

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