ASTM D7418-07
(Practice)Standard Practice for Set-Up and Operation of Fourier Transform Infrared (FT-IR) Spectrometers for In-Service Oil Condition Monitoring
Standard Practice for Set-Up and Operation of Fourier Transform Infrared (FT-IR) Spectrometers for In-Service Oil Condition Monitoring
SIGNIFICANCE AND USE
This practice describes to the end user how to collect the FT-IR spectra of in-service oil samples for in-service oil condition monitoring. Various in-service oil condition monitoring parameters, such as oxidation, nitration, soot, water, ethylene glycol, fuel dilution, gasoline dilution, sulfate by-products and phosphate antiwear additives, can be measured by FT-IR spectroscopy (5-8), as described in Practice E 2412. Changes in the values of these parameters over operating time can then be used to help diagnose the operational condition of various machinery and equipment and to indicate when an oil change should take place. This practice is intended to give a standardized configuration for FT-IR instrumentation and operating parameters employed in in-service oil condition monitoring in order to obtain comparable between-instrument and between-laboratory data.
SCOPE
1.1 This practice covers the instrument set-up and operation parameters for using FT-IR spectrometers for in-service oil condition monitoring for both direct trend analysis and differential trend analysis approaches.
1.2 This practice describes how to acquire the FT-IR spectrum of an in-service oil sample using a standard transmission cell and establishes maximum allowable spectral noise levels.
1.3 Measurement and integrated parameters for individual in-service oil condition monitoring components and parameters are not described in this practice and are described in their respective test methods.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D7418 − 07
StandardPractice for
Set-Up and Operation of Fourier Transform Infrared (FT-IR)
Spectrometers for In-Service Oil Condition Monitoring
This standard is issued under the fixed designation D7418; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This practice describes the instrument set-up and operation parameters for using FT-IR spectrom-
eters for in-service oil condition monitoring. The following parameters are typically monitored for
petroleum and hydrocarbon based lubricants: water, soot, oxidation, nitration, phosphate antiwear
additives, fuel dilution (gasoline or diesel), sulfate by-products and ethylene glycol. Measurement and
data interpretation parameters are standardized to allow operators of different FT-IR spectrometers to
obtaincomparableresultsbyemployingthesametechniques.Twoapproachesmaybeusedtomonitor
in-service oil samples by FT-IR spectrometry: (1) direct trend analysis and (2) differential (spectral
subtraction) trend analysis. The former involves measurements made directly on in-service oil
samples, whereas the latter involves measurements obtained after the spectrum of a reference oil has
been subtracted from the spectrum of the in-service oil being analyzed. Both of these approaches are
described in this practice, and it is up to the user to determine which approach is more appropriate.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice covers the instrument set-up and operation
D4057 Practice for Manual Sampling of Petroleum and
parameters for using FT-IR spectrometers for in-service oil
Petroleum Products
condition monitoring for both direct trend analysis and differ-
E131 Terminology Relating to Molecular Spectroscopy
ential trend analysis approaches.
E168 Practices for General Techniques of Infrared Quanti-
1.2 This practice describes how to acquire the FT-IR spec-
tative Analysis
trum of an in-service oil sample using a standard transmission
E1421 Practice for Describing and Measuring Performance
cell and establishes maximum allowable spectral noise levels.
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
eters: Level Zero and Level One Tests
1.3 Measurement and integrated parameters for individual
E1866 Guide for Establishing Spectrophotometer Perfor-
in-service oil condition monitoring components and param-
mance Tests
etersarenotdescribedinthispracticeandaredescribedintheir
E2412 Practice for Condition Monitoring of In-Service Lu-
respective test methods.
bricants by Trend Analysis Using Fourier Transform
1.4 The values stated in SI units are to be regarded as the
Infrared (FT-IR) Spectrometry
standard. The values given in parentheses are for information
only.
3. Terminology
1.5 This standard does not purport to address all of the
3.1 Definitions:
safety concerns, if any, associated with its use. It is the
3.1.1 For definitions of terms relating to infrared spectros-
responsibility of the user of this standard to establish appro-
copy used in this practice, refer to Terminology E131.
priate safety and health practices and determine the applica-
3.1.2 Fourier transform infrared (FT-IR) spectrometry,
bility of regulatory limitations prior to use.
n—form of infrared spectrometry in which an interferogram is
obtained; this interferogram is then subjected to a Fourier
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum
Products and Lubricants and is the direct responsibility of Subcommittee D02.96 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
In-Service Lubricant Testing and Condition Monitoring Services. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Dec. 1, 2007. Published February 2008. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7418-07. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7418 − 07
transform calculation to obtain an amplitude-wavenumber (or toring in order to obtain comparable between-instrument and
wavelength) spectrum. between-laboratory data.
3.2 Definitions of Terms Specific to This Standard:
5. Apparatus
3.2.1 condition monitoring, n—fieldoftechnicalactivityin
which selected physical parameters associated with an operat-
5.1 Fourier Transform Infrared (FT-IR) Spectrometer—All
ing machine are periodically or continuously sensed, measured FT-IR instruments suitable for use in this practice must be
and recorded for the interim purpose of reducing, analyzing,
configured with a source, beamsplitter and detector suitable for
comparinganddisplayingthedataandinformationsoobtained spectral acquisition over the mid-infrared range of 4000 to 550
-1
and for the ultimate purpose of using interim result to support
cm . The standard configuration includes a room temperature
decisions related to the operation and maintenance of the deuterated triglycine sulfate (DTGS) detector, an air-cooled
machine. (1, 2)
source, and a germanium-coated potassium bromide (Ge/KBr)
beamsplitter, although a zinc selenide (ZnSe) beamsplitter may
3.2.2 direct trend analysis, n—monitoring of the level and
also be used. The FT-IR spectrometer’s IR source and inter-
rate of change over operating time of measured parameters (2,
ferometer should be in a sealed compartment to prevent
3) using the FT-IR spectrum of the in-service oil sample,
harmful, flammable or explosive vapors from reaching the IR
directly, without any spectral data manipulation such as spec-
source.
tral subtraction.
3.2.3 differential trend analysis, n—monitoring of the level NOTE1—Photoconductivedetectorssuchasmercurycadmiumtelluride
(MCT) should not be used owing to inadequate linearity of the detector
and rate of change over operating time of measured parameters
response.
usingtheFT-IRspectraofthein-serviceoilsamples,following
5.2 Sample Cell—The sample cell employed for in-service
subtraction of the spectrum of the reference oil.
oil condition monitoring is a transmission cell with a fixed
3.2.4 in-service oil, n—lubricating oil that is present in a
pathlength that can be inserted in the optical path of the FT-IR
machine that has been at operating temperature for at least one
spectrometer. Cell window material and cell pathlength con-
hour.
siderations are stated below.
3.2.4.1 Discussion—Sampling an in-service oil after a short
5.2.1 Cell Window Material—ZnSe is commonly used as
period of operation will allow for the measurement of a base
the window material for condition monitoring and is recom-
point for trend analysis; the minimum sampling time should be
mended because of its resistance to water. Sample cells
at least one hour after oil change or topping-off.
constructed of materials other than ZnSe may be used;
3.2.5 reference oil, n—sample of a lubricating oil whose
however, to address all the various methods associated with
spectrum is subtracted from the spectrum of an in-service oil
condition monitoring, the window material should transmit IR
for differential trend analysis.
-1 -1
radiation over the range of 4000 cm to 550 cm . KCl and
3.2.5.1 Discussion—The most commonly employed refer-
KBr are common cell window materials that meet this require-
enceoilisasampleofthenewoil.Itshouldbenoted,however,
ment but these are water-soluble salts and should not be used
that the continued use of the same reference oil after any
if oil samples containing moisture are frequently run through
top-off of lubricant may lead to erroneous conclusions, unless
the cell, as contact with water will cause the windows to fog
the added lubricant is from the same lot and drum as the
and erode rapidly. In addition, Coates and Setti (4) have noted
in-service oil. This possibility is averted if a sample of the
that oil nitration products can react with KCl and KBr
in-service oil is taken after a short period of operation
windows, depositing compounds that are observed in the
following top-off of the lubricant (see 3.2.4.1) and is employed
spectra of later samples. On the basis of this report, KCl and
thereafter as the reference oil.
KBr windows should not be used with samples of gasoline or
natural gas engine oils as well as other types of lubricants
4. Significance and Use
where nitration by-products may form due to the combustion
4.1 Thispracticedescribestotheenduserhowtocollectthe
process or other routes of nitration formation.
FT-IR spectra of in-service oil samples for in-service oil
5.2.1.1 When ZnSe is used as the window material, the
condition monitoring. Various in-service oil condition moni-
reflections of the infrared beam that occur at the inner faces of
toring parameters, such as oxidation, nitration, soot, water,
the windows cause fringes to be superimposed on the oil
ethylene glycol, fuel dilution, gasoline dilution, sulfate by-
spectrum; these must be minimized using physical or compu-
productsandphosphateantiwearadditives,canbemeasuredby
tational techniques as presented in Appendix X1. Because KCl
FT-IR spectroscopy (5-8), as described in Practice E2412.
and KBr have lower refractive indices than ZnSe, the use of
Changes in the values of these parameters over operating time
these window materials avoids observable fringes in the oil
can then be used to help diagnose the operational condition of
spectrum.
various machinery and equipment and to indicate when an oil
5.2.2 Cell Pathlength—The standard cell pathlength to be
change should take place. This practice is intended to give a
employed for in-service oil condition monitoring is 0.100 mm;
standardized configuration for FT-IR instrumentation and op-
however, in practical terms, pathlengths ranging from 0.080 up
erating parameters employed in in-service oil condition moni-
to0.120mmaresuitable,withvaluesoutsidethisrangeleading
to either poor sensitivity or non-linearity of detector response,
respectively. The actual cell pathlength obtained can be deter-
The boldface numbers in parentheses refer to a list of references at the end of
this standard. mined from the interference fringes in the spectrum recorded
D7418 − 07
with an empty cell or by recording the spectrum of a check 8. Preparation and Maintenance of Apparatus
fluid; details for calculating cell pathlength are presented in
8.1 Rinsing, Washing and Check Solvents—A variety of
Appendix X2. The reporting units of the various in-service oil
hydrophobic solvents may be used to clean the cell and rinse
condition monitoring parameter test methods are based on a
the lines between samples as well as serving as a check fluid to
pathlength of 0.100 mm (see the respective test methods).
monitor pathlength. Typical solvents include hexanes,
Accordingly, all data must be normalized to a pathlength of
cyclohexane, heptane or odorless mineral spirits (OMS).
0.100 mm, either by multiplying all data points in the absorp-
Health and safety issues on using, storing, and disposing of
tion spectra by a pathlength correction factor (spectral normal-
check or cleaning/wash solvents will not be covered here.
ization) or by multiplying the results of the respective test
Local regulations and Material Safety Data Sheets (MSDS)
methods by a pathlength correction factor (see 10.2). The
should be consulted.
normalization procedure is usually part of the software pro-
8.2 Sample Cell and Inlet Filter—Thecellshouldbeflushed
vided by instrument manufacturers.
with the designated rinse/wash solvent at the start and end of
NOTE2—Forpurposesofinterlaboratorycomparisonofresults,spectral
analytical runs to clean the cell. Immediately following flush-
normalization should be performed.
ing of the cell, an absorption spectrum of the empty cell (see
5.3 Filter (optional)—The use of a particulate filter with a
9.1.2.2)shouldberecordedtocheckforbuild-upofmaterialon
mesh size of 0.100 mm or less to trap any large particles
thecellwindows.Ifaninletfilterisused,thefiltershallalsobe
present in the sample is strongly recommended to prevent cell
checkedforparticlebuild-upanditseffectonsampleflowrate.
clogging.
8.3 Check Fluid and Pathlength Monitoring—The purpose
5.4 Sample Pumping System (optional)—Apumping system
of a check fluid is to verify proper operation of the FT-IR
capable of transporting oil to be analyzed into the transmission
spectrometer/transmission cell combination, as well as any
cellandofemptyingandflushingthecellwithsolventbetween
associated sample introduction and cleaning hardware. It is
samples may be used instead of manual cell loading. Commer-
recommendedthatanabsorptionspectrumofthecheckfluidbe
cial vendors offer various pumping systems that may differ in
recorded when a new or re-assembled cell is initially used and
the type of pump, tubing, and transmission cell. Depending on
archived to disk as a reference spectrum against which subse-
the sample handling system employed and the viscosity of the
quent spectra of the check fluid may be compared. The
oils analyzed, a wash/rinsing solvent may be run between
spectrum of the check fluid may also be used to calculate the
samples to minimize sample-to-sample carryover as well as
pathlengthofthesamplecelltonormalizealldatato0.100mm
keep the cell and inlet tubing clean; commercial vendors may
and to monitor changes in the cell pathlength over time, where
recommend specific solvent rinse protocols.
significant changes may imply wear or contamination on the
5.4.1 Hydrocarbon Leak Alarm—When a sample pumping
cell windows and should prompt remedial action. To serve as
system is used, an independent flammable vapor sensor and
a check fluid, a solvent must have consistent spectral charac-
alarm system is strongly recommended The purpose of this
teristics (lot-to-lot) and a measurable (on-scale) IR absorption
alarm system is to alert the operator when a leak occurs in the
bandforcellpathlengthcalculation;formoredetails,seeX2.2.
tubing, connectors or transmission cell.
One IR manufacturer uses heptane, another uses OMS, and
4,5
other commercial products are available.
6. FT-IR Spectral Acquisition Parameters
6.1 The spectral acquisition parameters are specified below.
9. Procedure for Collecting FT-IR Spectra
Because the spectral resolution, data spacing, and apodization
9.1 Background Collection—Collect a single-beam back-
affect the FT-IR spectral band shapes, these specifications must
ground spectrum at the beginning of each run and frequently
be adhered to:
-1
enough thereafter such that changes in atmospheri
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