6.4.

4 Lube Oil Analysis

Lube oil analysis is a useful tool in trending the wear that occurs within an engine. It
allows for early detection of problems and ensures the lubricating quality of the oil.
Samples must be taken at regular intervals. The most effective way to determine the
condition of the lube oil is by conducting a spectrochemical analysis and a physical
properties test. Asp ectrochemical analysis measures the amount of wear metals and
other contaminants. The physical properties test checks the lube oil quality. Other tests
that should be conducted are oil foaming and optical particle count.
Determining the quality of lube oil is more than the wear metal concentration levels. The
overall trend (increasing, decreasing or stable) of the metals must be considered. The
other factors are the physical properties of the oil and external sources of
contamination.
SPECTROCHEMICAL ANALYSIS
Spectrochemical analysis measures the quantity of various elements in a lube oil
sample.
The elements listed in Table 6.4.3 are identified and measured by the spectrometer.
Wear Metals
Over extended time periods, metal-to-metal contact will result in surface wear and
debris
in the oil. The key to effective oil analysis is tracking the level of wear metals over time.
The
composition and concentration of wear metal debris depends on the equipment
materials
and the volume of oil. Because of the large volume of oil used in turbine engines, the
ratio
of wear debris to oil volume is low. With the start-up of new equipment, a certain level
of wear debris is generated as rotation clearances are established. Iron, lead, copper,
chromium, aluminum, nickel, silver, antimony, and tin are elements that indicate wear.
In monitoring wear metal concentrations, gradual or abrupt increases indicate excessive
wear. Refer to Table 6.4.3 for wear metals sources.
6.4.3. Table Wear Metals and Potential Sources
Wear Metals Potential Sources
Iron Accessory drive gearbox gears and bearings. Generator set reduction
gearboxes. Compressor set speed increasing and decreasing
gearboxes.
Copper Engine bearing and seals, thrust bearings, bearing cases (bronze),
accessory drive gearbox bearings, gas compressor bearings and seals,
Babbit material, reduction gearbox bearings, accessories (pumps), and
oil coolers.
Tin Engine bearings and seals, thrust bearings, reduction gearbox bearings,
speed increasing and decreasing gearboxes, gas compressor bearings
and seals.
Silver Engine bearing overlays and seal overlays.
Antimony Reduction gearbox bearings and radial bearing Babbit material.
Aluminum Present in labyrinth seal of gas compressors and in buffer gas seals.
Lead Engine bearings and seals, thrust bearings, reduction gearbox bearings,
speed increasing and decreasing gearboxes, gas compressor bearings
and seals.
Contaminants
Contamination is associated with substances entering the lube oil system from an
outside
source. The most common probable cause of contaminants is sample contamination or
incorrect oil replenishment procedures. Silicon in the form of silicon dioxide is one of the
most common contaminants and is the element that indicates the presence of dirt, sand,
or dust in the oil. Other sources of silicon include seals, grease, antifoam and coolant
additives. Any silicone level greater than 5 ppm should be considered abnormal. Wear
metals are also a form of abrasive contaminants.
Oil Additives
Oil additives are chemical compounds added to oils to create new fluid properties,
enhance properties already present, and reduce the rate at which undesirable changes
take place in the oil during service life. Zinc, phosphorus, calcium, barium, and
magnesium
are the elements that could be blended into the various lubricants by the manufacturers.
Phosphorus and zinc act as anti wear elements by coating the wetted parts and
reducing
friction. Calcium, barium, and magnesium are dispersants and detergents that flow
through the system, pick up wear and contaminant particles, and carry them to the filter
for removal from the oil. Potassium compounds are used as corrosion inhibitors, but
may
also be found as a mineral salt in sea water. Some anticorrosion additives can have
adverse effects on other oil properties. The additives must be properly formulated.
Zinc
Solar Engineering Specification 9-224 calls for less than 50 ppm in new oil, that is, 50
ppm
as an oil additive (not a contaminant or residue). Typically, oils containing zinc additive
will have as much as 600 ppm zinc. Zinc causes sludge formation and galvanic attack of
silver plating. These oils should not be used.
Coolant Additives
Sodium and boron are used as corrosion inhibitors and anti oxidants in reciprocating
engines and will not generally show up with gas turbines. Sodium, however, may also
enter the system as a contaminant from salt water or sea air.
PHYSICAL PROPERTIES TEST
Physical properties tests consist of a series of related tests to determine the
classification,
contamination, and degradation of a lubricant. The following paragraphs describe what
is
measured by the physical properties test:
Fuel Dilution
Fuel dilution is ameasurement of the amount of unburned liquid fuel present in the
lubricant
and is determined by a distillation or flash test. This test will indicate such problems as
fuel
pump leakage into the accessory gear housing.
Water
Water present in the lube oil system is abnormal. The water test, when run in
conjunction
with other related tests, indicates emulsification of the lubricant from an outside source
of
contamination or condensation. When water is present in concentrations of 2000 ppm or
more, the oil is condemned unless the concentration can be reduced below that limit by
centrifuging or other methods.

Viscosity
Viscosity is the measure of the flow rate of a lubricant at a given temperature in relation
to time. This test is indicative of a lubricant classification by grade, oxidation, and
contamination. Solar Engineering Specification 9-224 lists the viscosity requirements for
new oil. Lube oil must be replaced if the viscosity increases or decreases from the
original
viscosity by more than the percentages shown in Table 6.4.4.
Neutralization Number
Neutralization number is a number expressed in milligrams of a substance required to
neutralize ten grams of lubricant. This test is used to show the relative changes in a
lubricant. The neutralization number is reported as a Total Acid Number (TAN). A high
TAN usually means overheated or oxidized oil. If the TAN test shows a significant
increase
in acidity since the last test, a Rotary Bomb Oxidation Test (RBOT) should be
performed.
Total Base Number (TBN) is a measurement of the reserve alkalinity remaining in the
lubricant and is typically used with engine and hydraulic oils, not with turbine oils.
FOAMING TEST
Foaming is the formation of a layer of bubbles on the surface of the oil. Foaming
becomes
a problem when it is capable of hindering the normal drainage of oil back to the lube oil
reservoir. Oil foaming can be reduced by the addition of antifoam compounds to the
lube
oil, however, all possible mechanical contributions should be investigated and
eliminated
first. The improper addition of antifoamant can cause air entrainment in the oil. The test
used to measure foaming tendencies and the stability of the foam is described in ASTM
D-892.
OPTICAL PARTICLE TEST
The optical particle test determines oil cleanliness. Solar uses a modified ISO
4406:1999
standard to establish the relationship between particle counts and cleanliness. This
standard provides a three part code to specify the number of particles per milliliter of
oil that is greater than or equal to 2 micrometers (μm), 5 μm, and 15 μm respectively.
Each code number correlates to a particle concentration range and can be found in ISO
4406:1999. Solar specifies a cleanliness standard code of 16/14/12.
AIR ENTRAPMENT
Air entrainment (aeration) consists of small bubbles trapped beneath the surface of the
oil. Air trapped within the oil will reduce the film strength of the oil causing problems with
physical contact between the shafts and bearings and the meshing of gear teeth.
Entrained
air in the lube oil can also cause hose vibration

SAMPLING PROCEDURES
Asam ple is collected in a clean sample bottle from a valve located in a flowing bearing
supply line or is drawn from the middle of the oil reservoir (tank) after the oil has been
thoroughly mixed. It is then sent to a laboratory for analysis. Asp ectrochemical analysis
is conducted to measure the amount of various wear metals in the oil, and physical
properties tests are done to monitor oil quality. The key to effective oil analysis lies in
the
determination of changes over time. Samples must be taken at regular periodic intervals
for the program to function properly.
Correct labeling of an oil sample is extremely important. An improperly labeled oil
sample
is useless if its analysis results cannot be matched to a particular package.
The label should show the following information:
• Sampling date
• Name of the company
• Solar package serial number
• Engine hours since last overhaul
• Hours since last oil change
• Amount of oil added since last sampling
• Type of oil used
• Type of fuel used
For generator sets, samples should be taken while the engine is operating and after oil
has
attained normal operating temperature. This will ensure that particle concentrations
have
achieved a uniform distribution throughout oil. It is also preferable to have a load on the
engine during this time to ensure highest equilibrium level of wear-metal concentration.
For compressor and mechanical drive sets, samples must be taken only after engine
shutdown. Prior to shutdown, the engine should attain normal operating temperature,
preferably under loaded conditions.
All gas compressor sets mayco ntain potentially explosive
gas mixture in the lube oil tanks during engine operation and
after shutdown. Strict compliance with Solar Service Bulletin
13.2/101 is required.

NOTE
Do not insert sampling tube so deep as to pick up sediment or
debris from the bottom of reservoir R901. Even small amounts
of sediment will significantly affect analytical results of the
sample.
TEST RESOURCES
Variances in the sampling and measurement techniques used by different labs can yield
different results. Using a consistent sampling method and reliable lab are important if
valid
trends are to be established. For any questions regarding lube oil testing or problems,
contact the closest Solar District Office. Oil testing for other purposes should be
conducted
independently.
OIL REPLACEMENT CRITERIA
Solar Engineering Specification 9-224 establishes the requirements for new oil and lists
specific oil replacement criteria for used oil. The criteria requiring maintenance and/or
oil replacement are listed in Table 6.4.4. Whenever a spectrochemical analysis is done,
the sample should also be tested for color, odor, viscosity, water content, and particle
contamination.
6.4.4. Table Lube Oil In-Service Limits
Property Limits (compared to new oil)
Water Maximum 2,000 ppmw
Viscosity +20% or -10%
Total Acid Number (TAN) Increase of 0.4 mgKOH/g (for all oil types) or:
0.8 mg KOH/g maximum for synthesized
hydrocarbon oils (Class I oils)
0.6 mg KOH/g maximum for petroleum oils (Class II oils)
2.0mg KOH/gmaximum for synthetic ester oils (Class III oils)
0.2 mg KOH/g maximum for phosphate ester oils (Class
IV oils)
Rotary Bomb Oxidation Test
(RBOT)
25% of original (new oil) value
Foaming Characteristics Sequence I - 300/10 Sequence II- 300/10 (Guideline only,
refer to Section 4.3.3 of ES-9-224).
Air Release at 122°F (50°C) 10 minutes maximum
(Guideline only, refer to Section 4.3.4 of ES-9-224).