5/16/2015
Outline
 Introduction to Water Contamination Testing in Turbines and Industrial Lubricants
 Water Determination by Infrared Spectroscopy and its Limitations
 Building A New “Total Water” Calibration by Infrared Spectroscopy
 Results and Conclusion
Accurate Total Water
Measurement for On-Site
Analysis of Turbine Oils
by Infrared Spectroscopy
Randi Price
STLE, May 19, 2015
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Turbine Oils
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Water Measurement by Karl Fischer Titration
 Turbine oils are typically formulated to
have
 The most widely accepted method for
detecting water in oil is by Karl Fischer
titration (KF, ASTM D6304).
 High thermal stability
 Oxidation resistance
 Excellent water separation
 Can be very accurate
 Detects all phases of water in a sample:
dissolved, free, or emulsified
 Severe water contamination in a lubricant
is a major problem.
 Turbine manufacturers generally
recommend very low limits of water,
alarms at or below 1000 ppm (0.1%)
water.
 Water measurement is part of a lubricant
condition monitoring program.
 However, it may not be realistic for to
do this on-site:
 Requires hazardous reagents ($)
 Needs careful sample preparation by a
skilled lab technician ($$)
 Uses expensive equipment ($$$)
 Lubricant Chemistry:
 Oxidation
 Water contamination
 Total Acid Number
 Particle Count
 Elemental
 Typically takes 5-15 minutes for analysis
 Sending samples to an external lab
may take several days to a week to get
results—too long to always prevent a
critical failure!!
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On-Site Water Measurement
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On-Site Water Trending by IR
 Screening/trending tests: qualitative, semi-quantitative, quantitative
 Infrared Spectroscopy
 Accuracy of tests are always compared to referee method: Karl Fischer
 Chemical-free measurement
 Can be very easy to run and interpret
 Quantitative results
 Crackle Test
 Widely accepted (ASTM E2412), but not widely adopted…why??
 Simple equipment used ($)
 Requires an experienced operator for semi-quantitative analysis ($$)
 Calcium Hydride Kits
In a very general sense, spectroscopy is the study between the interaction of radiated
energy and matter. A spectrometer consists of a radiative source, a detector, and a
computer or other converter of the detector signal to useful information.
 Corrosive reagents required ($$)
 “Per Sample” cost ($)
 Semi-quantitative to quantitative when used correctly.
I0
 Relative Humidity Sensor
I
A
 Solvent-free
 About same cost as KF ($$$)
 Easy to use for quantitative ($)
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5/16/2015
The Problem with Water Measurement in Machinery Oils
Example: Turbine Oils
 Infrared spectroscopy is GREAT for measuring dissolved water in oils.
 Turbine oils have excellent water separation.
 ASTM Standard Practice E2412
0.5% water
0% water
 However, a lot of industrial oils have excellent water separation.
 The saturation limits can be on the order of 100 ppm (0.01%).
 Dissolved water measurement will not detect moderate to severe water
contamination!
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Example: Turbine Oils
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Example: Turbine Oils
 Turbine oils have excellent water separation.
 Turbine oils have excellent water separation.
 Not much dissolved water is present!
 Not much dissolved water is present!
 So typical water determination methods as in E2412 are ineffective for practical
water measurement.
Traditional IR Result:
Water = 38 ppm
???
???
No dissolved water peak!
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Example: Turbine Oils
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Methods to Dissolve Water in Oil
 Is it possible to dissolve the water in oil by physical methods?
 Agitation: Shaking, Stirring, Homogenizing
 Works only for degraded oils when the separation additives are broken down.
 Turbine oils are kept pretty fresh…
Traditional IR Result:
 This method doesn’t really work.
 The best approach to dissolve water in oil seems to be with surfactants
Water = 38 ppm
???
???
Dissolved Water Peak can be
detected in the presence of
surfactant!
Dashed = new oil
Red = oil with 1120 ppm water
Blue = oil with 1120 ppm water + stabilizer
“Another solution is needed for turbine oils!”
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Frank Higgins and John Seelenbinder. “Onsite FTIR quantitative analysis of water in mineral-based oils using a novel water stabilization technique” Application Note: Energy and fuels.
Agilent Technologies. Danbury, CT, USA.
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How Does IR Spectroscopy Work?
 Infrared spectroscopy uses vibrational modes to analyze the molecules present in
a sample.
 Vibrational Modes:
 Molecules absorb specific frequencies according to their structure.
Is there a chemical-free, portable measurement
method by infrared spectroscopy for water in turbine
(and other industrial) oils?
 Molecules that are IR active experience a change in dipole moment.
Can you measure water by IR that is not dissolved?
The Symmetric Stretch (Example shown is an H2O molecule at 3685 cm-1)
The Asymmetric Stretch (Example shown is an H2O molecule at 3506 cm-1)
Bend (Example shown is an H2O molecule at 1885 cm-1)
These vibrational modes show up as peaks in the infrared spectrum.
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Water in Turbine Oil Spectra
I0
I
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http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Vibrational_Modes
Water in Turbine Oil Spectra
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I0
I
A
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Chemical information from the peaks…
However, there is also Physical information from the baseline lift!!
(the transmitted light I0 is universally decreasing in this range)
(which chemical bonds are present in the sample)
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Baseline Lift Due to Light Scattering
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A new chemical-free, portable measurement for “Total Water”!
 Discrete water droplets in oil
scatter light.
 Using a portable infrared fixed-grating spectrometer, a calibration was developed
for determining “Total Water” content in turbine oils.
 Scattered light appears as a
uniform lift in the baseline.
 The magnitude of the scattering
depends on:
 The number of droplets.
 The size of the droplets.
 Calibration prepared from 33 samples of 5 different oils:
 Authentic in-service Chevron GST 32 samples obtained from a power generation plant
(water contaminated).
 Water mixes of popular brands of industrial oils (turbine, bearing, and gear oils):
 Shell Turbo T32
 Shell Turbo T68
A dual approach of using the traditional IR peak for dissolved water and the
baseline lift due to light scattering can be used to develop a calibration for “Total
Water”!
Augusto M. Araujo, Leila M. Santos, Montserrat Fortuny, Rosana L. F. V. Melo, Raquel C. C. Coutinho, Alexandre F. Santos. Energy & Fuels 2008, 22, 3450-3458.
 Shell Morlina S4 B150
 Royal Purple Thermyl-Glyde 680
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Sample Preparation is Key!
Collecting and Analyzing Data
 Baseline lift due to light scattering has to be consistent and repeatable in order
to create a reliable calibration.
 Homogenized samples were measured by the
reference method and IR.
 Light scattering depends on the number of water droplets.
 Karl Fischer ASTM D6304
 Light scattering also depends on the size of water droplets.
 Mid-IR (FluidScan)
 Samples must be as homogeneous as possible to minimize sampling errors.
 This is CRITICAL to the method.
 Use the same aliquot of sample (drawn up in a
pipette) to test both methods:
 KF measured in triplicate, 7 drops
 IR spectra measured in duplicate, 2 drops
A homogenizer will create uniform droplet
sizes and disperse the water droplets
uniformly in the oil media.
 X variables = IR spectra
 Y result = KF values
Homogenize 30 sec on high power, wait 1
minute before analysis.
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Multivariate Calibration Results
 Validation samples not used in the calibration set.
 Wider range of oil brands and types.
 <10,000 ppm water “low” calibration
 Calibration is universal for “industrial oils”.
 Success!
“high” calibration
CAL “LOW”
3468 – 3810 cm -1
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Validation
 Two calibration ranges developed:
 >9,000 ppm water
Image : Unscrambler X , CAMO Software
CAL “HIGH”
3468 – 3810 cm -1
Correlation to KF titration of R2 > 0.95 for all industrial oils tested over the range
1,000 to 30,000 ppm (0.1 – 3%) water
A successful PCR (Principal Component Regression) calibration was achieved for
determining “Total Water”.
IR Spectroscopy correlation to KF result: R2 > 0.98 for the calibration samples
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Repeatability
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Effect of Sample Preparation
 The calibration is dependent on consistent distribution of water droplets in the oil
sample.
 Measure samples on separate days using good sampling technique with the
homogenizer.
 Simultaneously test both methods: KF and FS/IR on the same sample aliquot.
 Group A: Samples were homogenized for 30 seconds.
 Group B: Samples were vigorously hand-shaken for 30 seconds.
Sample
Diff FS
(ppm)
Diff KF
(ppm)
B2
171
135
31%
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A3
114
%Diff FS %Diff KF
25%
14%
2%
E7
136
467
4%
19%
B7
2227
2575
44%
46%
E6
1493
45
19%
E8
2081
59
11%
0%
E4
2435
4051
13%
23%
E3
3900
7049
20%
24%
0%
(Just because it looks homogeneous,
does not mean that you have uniform
water droplets!)
Both IR and KF are susceptible to sampling errors.
The proposed IR method has similar repeatability to KF. Typical repeatability for
moderate to severe water contamination (>1,000 ppm) is ~20%.
The hand shaken samples measured by the IR method correlate poorly to KF.
The homogenizer is an important component of the method.
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Conclusion: Measuring “Total Water”
 Water contamination testing in turbine and other industrial lubricants is an
important part of a machinery condition monitoring program.
 The most widely accepted method, Karl Fischer titration (ASTM D664), is not easy
to do on site and sending samples to an external laboratory may take several
days.
 Infrared spectroscopy is easy, but traditional IR measurements for water fail to
quantify any free or emulsified water that is present and will fail to detect moderate
to severe water contamination.
 A new infrared spectroscopy method which combines easy sample preparation
and a multivariate calibration delivers an accurate, repeatable total water
measurement compared to Karl Fischer titration.
Questions??
New IR Result:
+
+
=
Water = 5,838 ppm
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