NB/SH/T 0853-2010 In-service lubricant condition monitoring method Fourier transform infrared (FT-IR) spectroscopy trend analysis method

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Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: NB/SH/T 0853—2010
• Chinese name: In-service lubricant condition monitoring method Fourier transform infrared (FT-IR) spectroscopy trend analysis method
• English name: Standard practice for condition monitoring of used lubricants by trend analysis using fourier transform infrared (FT-IR) spectrometry
• Replacement relationship: first publication (original text: this standard is first published)
• Adoption relationship: modified adoption of ASTM E2412-04
• Publication/implementation: published on 2011-01-09, implemented on 2011-05-01
• Publishing unit: National Energy Administration
• Custodian: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Lubricant Oil Change Indicators (SAC/TC280/SC6)
• Drafting unit: Sinopec Research Institute of Petroleum Processing
• Main drafter: Yang Yurui

2. Scope of application and non-applicability

• Applicable (1.1): applicable to monitoring, by FT-IR spectroscopy, additive depletion, accumulation of contaminants, and degradation of the oil in mechanical lubricating oils, hydraulic oils, and other liquids used in routine operation of mechanical equipment.
• Contaminant monitoring includes (1.1): water, soot, glycol, fuel, and indeterminate oil.
• Degradation monitoring (1.1): when the lubricating oil shows signs of degradation, oxidation, nitration, and sulfation products can be monitored.
• Purpose (1.1): to diagnose the operating condition of machines based on the quality of the in-service lubricating oil; the measurement method and data interpretation parameters allow provision to different FT-IR spectrometer operators so that results can be compared using the same technique.
• Method basis (1.2): based on trend analysis and distribution response analysis by mid-infrared spectroscopy.
• Not applicable (1.4): cannot be used to measure metal wear and elemental analysis; not applicable to predicting the physical properties of lubricating oils (for example, viscosity, total base number, total acid number, etc.).
• Purpose limitation (1.4): the purpose is to monitor in-service lubricating oil and assist in determining the condition of conventional mechanical equipment, not to analyze the composition, lubricating performance, or additive formulation of the lubricating oil, etc.
• Scope and distribution overview are for reference only (1.3): not to be used as criteria for establishing lubricating oils or mechanical equipment.
• Safety (1.5): this standard does not propose recommendations for all safety issues involved; before use, users must establish appropriate safety and protection measures and determine the applicability of relevant regulatory restrictions.
• Note (1.2): establishing or recommending normal, warning, caution, or alarm limits for any machine is not the purpose of this standard; such limits should be established by recommendations and guidance jointly provided by the machine manufacturer and the maintenance organization.

3. Method principle

• 4 Summary: sample from the engine or equipment being monitored, and under conditions of sufficient signal-to-noise ratio (S/N), collect the infrared spectrum of the sample in the range 4000cm⁻¹ to 550cm⁻¹, and measure the corresponding absorption peak areas.
• The precise data acquisition parameters depend on the choice of instrument; the original text states that "most systems should be able to acquire a suitable absorption spectrum within one minute".
• Measure and report the molecular functional groups or features of the infrared spectrum (i.e., water, fuel, antifreeze, additives, degradation products, etc.), and based on the level of the monitoring system and trend analysis, condition warnings and alarms can be triggered.
• 5 Significance: periodic sampling and analysis of lubricating oil has long been used as a means of diagnosing the condition of individual mechanical equipment; atomic emission (AE) and atomic absorption spectroscopy (AA) are often used for metal wear analysis (for example GB/T 17476); the physicochemical properties of lubricating oil and metal wear analysis are used to provide information on lubricating oil quality (for example SH/T 0251 and GB/T 11133); through FT-IR spectroscopy, molecular species analysis of lubricating oils and hydraulic oils can directly produce the expected molecular composition information, including additive depletion, oil degradation products, and foreign matter contamination, etc., supplementing metal wear analysis and other physicochemical property analyses in machine condition monitoring programs.
• 3.1 Definition: Fourier transform infrared (FT-IR) spectroscopy—a form of infrared spectroscopy in which an interferogram is obtained, and the interferogram is Fourier transformed to obtain an amplitude-wavenumber (or wavelength) spectrum.

4. Reagents and materials (purity / preparation)

• 6.1.2 Sample cell window material: ZnSe, NaCl, or KBr (original text: the sample cells used for the data in this standard are made of ZnSe, NaCl, or KBr materials).
• 6.1.2 Window transmission range (original table, source-text extraction doubtful point annotation):
  • ZnSe: 4000 to 550 (requires confirmation against the source standard (source-text extraction))
  • KBr: 4000 to 400 (requires confirmation against the source standard (source-text extraction))
  • NaCl: 4000 to 650 (requires confirmation against the source standard (source-text extraction))
  • There are also values such as 4000 to 850, 4000 to 100, etc., and the corresponding materials require confirmation against the source standard (source-text extraction)
• 6.1.2 Path length: 0.100mm (100μm); acceptable path length range 0.108μm to 0.0120mm (the original numerical value is suspected to have a source-text extraction error, requires confirmation against the source standard (source-text extraction)); exceeding this path length range will cause nonlinearity.
• 6.1.2 Cleaning solvent: analytical grade solvent, such as heptane or cyclohexane (original text mentions "such as heptane or cyclohexane"); refer to the chemical safety data sheet before use.
• 6.2.5 Check fluid: commercially available n-heptane already used by infrared manufacturers may be used; the check fluid should be consistent with the method results used in the appendix of this standard; used to check whether the FT-IR spectrometer, transmission cell device, and related sample introduction system and cleaning components are normal.
• Appendix B.2.1 Water standard sample: prepare on site by adding water to drying oil; the sample should be freshly prepared and analyzed, and thoroughly mixed to ensure valid results; use ultrasonic oscillation or mechanical shaking for at least 15min; plastic containers must not be used.
• Appendix B.2.8.5 Glycol standard sample: mix glycol antifreeze and water at 50:50 to prepare a glycol standard sample with a mass fraction of 0.1% to 0.5%; it should be calculated based on the actual amount of glycol antifreeze added, not the integer of the 50:50 mixture; freshly prepared and analyzed; thoroughly mixed for at least 15min or more; plastic containers must not be used.
• Appendix B.2.7.4 Aged fuel calibration sample: diesel fuel must be heated to about 107°C and maintained at 30min, to about 5% of the original volume; gasoline is heated at low temperature until about 40% of the original volume; pay attention to fire prevention and exposure risks.

5. Instruments and equipment

• 6.1.1 Fourier transform infrared spectrometer (FT-IR): equipped with a light source, beam splitter, and detector covering the mid-infrared region of 550cm⁻¹ to 4000cm⁻¹ (the original numerical values are suspected to be 550cm⁻¹ to 4000cm⁻¹, requires confirmation against the source standard (source-text extraction)).
• 6.1.1 Detector: most instruments use a room-temperature deuterated triglycine sulfate (DTGS) detector, an air-cooled light source, and a germanium-coated potassium bromide (Ge/KBr) beam splitter.
• 6.1.1 Alternative light source, beam splitter, and detector combinations are commercially available, but have not been studied in this standard; other types of detectors may also be applicable, but caution is required, especially for nitrogen-cooled mercury cadmium telluride (MCT) compound semiconductor detectors with significant nonlinearity.
• 6.1.2 Infrared liquid transmission sample cell: may be made of zinc selenide (ZnSe), barium fluoride (BaF2), potassium bromide (KBr), or other window materials, with a path length of 0.100mm (100μm).
• 6.2 Sample introduction system: pump system for the transmission cell; if the oil is stored upright, it may contain particles larger than 10mg to prevent clogging of the transmission cell; if a particulate filter is not used, clogging may occur.
• 6.2.3 Sealed sample compartment: capable of preventing harmful, flammable, or explosive gases from entering the infrared light source.
• 6.2.4 Oil and gas leakage alarm: use a flammable gas sensor and alarm device for the sample introduction pump system, so that when a leak occurs in tubing, connectors, or the transmission cell, the operator can be promptly alerted.
• 6.2.5 Check fluid: used for quality control and procedure checks, and for comparison with other laboratories.

6. Recommended operating conditions

• 8.1.1 Spectral resolution: 8cm⁻¹ or higher (lower numerical value).
• 8.1.2 Data point interval resolution: 4cm⁻¹ or higher (lower numerical value).
• 8.1.3 Spectral range: 4000cm⁻¹ to 550cm⁻¹ (see 6.1.2).
• 8.1.4 Spectral form: absorbance as a function of wavenumber.
• 8.1.5 Other optical, electronic filtering, and interferogram calculation parameters: should be recommended by the instrument manufacturer or serve as necessary conditions for determining instrument quality; individual parameter settings will depend on the instrument manufacturer, but most FT-IR spectrometers should be able to acquire a suitable spectrum within one minute.
• 8.1 Note: the same scan acquisition parameters should be used for consistency in trend analysis of all samples.
• 8.2.1 Background acquisition: a single-beam background should be acquired frequently (empty system reference scan and background stored on the FT-IR spectrometer); the frequency of background acquisition should be determined by the conditions of each laboratory and the sample introduction technique; for example, when using an autosampler for sample introduction, complete the background scan before each sample spectrum acquisition.
• 8.2.2 Water vapor check: the average baseline points at 1609cm⁻¹ to 1582cm⁻¹ may be used and the overlapping peaks of water vapor at 1540cm⁻¹, 1559cm⁻¹, and 1652cm⁻¹ in the single-beam spectrum may be measured against the average baseline; an acceptable operating limit, for example, is that the water vapor overlapping peaks measured in the single-beam background should not exceed 10% of the single-beam intensity.
• 8.2.3 Background acquisition frequency: in extensive research and development work using this standard, background acquisition should be at least once every 2 hours.
• 8.3 Sample cell path length check: necessary for verifying the consistency of the sample cell; for results, refer to the 0.100mm path length correction mentioned in 6.1.2; it is more important for water-soluble salt plate sample cells (for example KBr); for systems using a fixed flow cell, the check can be completed at the same time as background acquisition; the method for measuring sample cell path length by baseline interference fringe is discussed in the appendix (see Appendix D).
• 9.1 Sample introduction: introduce the sample manually or with an automatic pump sample introduction system into the sample cell of the infrared spectrometer; autosamplers of different capacities provided by different manufacturers may all be used.
• 9.2 Sample integrity check: the spectral range of 3000cm⁻¹ to 1090cm⁻¹ will be used to evaluate many types of lubricating oils; the precise absorption intensity depends on the spectral resolution and the path length of the sample cell used.
• 9.2.1 The maximum absorption of petroleum-based lubricating oils is at 3000cm⁻¹ to 2800cm⁻¹ (transmission value near 0%T).
• 9.2.2 The maximum absorption of ester-based lubricating oil is in the range of 1390cm⁻¹ to 1090cm⁻¹ (transmittance value close to 0%T).
• 9.3 Cleaning and inspection of the sampling system: rinse the sample cell with a small amount of the next sample or a volatile solvent and dry it; after drying, the maximum absorbance of the sample cell should be below the preset threshold of the monitoring region (i.e., the CH stretching vibration of petroleum-based lubricating oil); for most petroleum-based lubricating oils, synthetic lubricating oils, and cleaning agents, the absorption intensity should be less than 0.2 absorbance units; the optimal threshold should be determined by the specific system configuration.
• 9.4 Data processing: all spectra are expressed as a function of absorbance versus wavenumber; before reporting, the calculated data must be corrected with reference to the 0.100mm optical path length.
• 9.4.1 Direct trend: through spectral data processing results, the spectral change trend of the in-service lubricating oil can be directly obtained; the best spectral data processing is spectral correction or correction with reference to the 0.100mm reference optical path length, and if necessary, spectral interference fringe reduction algorithms can also be applied.
• 9.4.2 Spectral subtraction: the difference spectrum produced by subtracting the new oil reference spectrum from the in-service lubricating oil spectrum; the spectra of the in-service lubricating oil and the new oil reference must be corrected with reference to the 0.100mm optical path length before spectral subtraction, and a subtraction factor of 1:1 should be used.
• 9.4.2.1 The most commonly used reference sample is new oil; if possible, the new oil should be from the same batch and same package as the in-service lubricating oil; a more representative reference oil is a lubricating oil sample collected after reaching operating temperature for 1 hours.
• 9.4.3 Final analysis data processing can also employ multiplication and other scaling techniques; for example, to facilitate evaluation and expression by maintenance personnel, "value ×100" can be used (see Appendix A).
• 9.5 Sample spectral analysis data: the selected spectral region should contain the relevant condition monitoring information to be measured and reported; the analysis regions for different types of lubricating oils are specific; when starting a lubricating oil analysis program, the parameters of a new oil sample can serve as the starting point for the change trend.

7. Sampling and Sample Preparation

• 7.1 Sample collection: sampling is to obtain a fully representative test sample; laboratory samples should be collected in accordance with the requirements of GB/T 4756.
• 7.2 Sample preparation: there are no special requirements for sample preparation; the laboratory sample should be shaken well during spectral acquisition to ensure that the sample taken from the bottle is representative.
• 3.5 Definition of in-service oil: lubricating oil that is in use and has been running at the machine's operating temperature for at least 1 hours; sampling after 1 hours of operation allows measurement of a baseline point for subsequent trend analysis; adding any lubricating oil to the machine after sampling (for example, the original added lubricating oil may change the baseline point of the trend) may lead to erroneous monitoring results.
• 3.6 Definition of new oil: lubricating oil drawn from the original packaging before being added to the machine.
• 3.7 Definition of reference oil: the complete definition is not provided in the available source (source-text extraction truncated).

8. Analysis Procedure

• 9.1 Sample introduction: introduce the sample manually or with an automatic pump sample introduction system into the sample cell of the infrared spectrometer.
• 9.2 Sample integrity check: inspect the infrared spectrum of the sample to prevent the sample cell from not being completely filled or having bubbles during data acquisition, which could affect the results; the spectral acquisition software should include an automatic inspection program.
• 9.3 Cleaning and inspection of the sampling system: rinse the sample cell with a small amount of the next sample or a volatile solvent and dry it; after drying, the maximum absorbance of the sample cell should be below the preset threshold of the monitoring region.
• 9.4 Data processing: all spectra are expressed as a function of absorbance versus wavenumber; before reporting, correction must be made with reference to the 0.100mm optical path length.
• 9.4.1 Direct trend method: spectral correction or correction with reference to the 0.100mm reference optical path length, and if necessary, apply spectral interference fringe reduction algorithms.
• 9.4.2 Spectral subtraction method: subtract the new oil reference spectrum from the in-service lubricating oil spectrum; before subtraction, correction must be made with reference to the 0.100mm optical path length, using a subtraction factor of 1:1.
• 9.4.2.1 Reference sample selection: the most commonly used reference sample is new oil; if possible, the new oil should be from the same batch and same package as the in-service lubricating oil; a more representative reference oil is a lubricating oil sample collected after reaching operating temperature for 1 hours.
• 9.4.3 Final analysis data processing: multiplication and other scaling techniques can also be used, for example, "value ×100".
• 9.5 Sample spectral analysis data: the selected spectral region should contain the relevant condition monitoring information to be measured and reported; the parameters of a new oil sample can serve as the starting point for the change trend.
• Appendix A (Normative Appendix) Measurement of Molecular Parameters—Direct Trend Method:
  • A.1 Purpose of this appendix: introduces typical lubricating oil measurement parameters for petroleum-based lubricating oils (e.g., crankcase oils), extreme pressure anti-wear lubricating oils, and ester-based oils; when data for other types of lubricating oils become available, they can also be added to this appendix.
  • A.2 Petroleum-based lubricating oil (typical diesel engine oil): condition monitoring is divided into contaminant monitoring (usually water, soot, glycol) and lubricating oil degradation monitoring (usually oxidation value and nitration value, etc.); sulfonation degradation products may be produced by degradation of lubricating oil components, but are usually formed as by-products of sulfur in diesel fuel; measurement of gasoline contamination is also possible, and a small number have been included in condition monitoring programs, but it has not been widely applied; in addition, the content of the anti-wear component zinc dithiophosphate in the composite additive can also be monitored.
  • A.2.1 Water: by measuring the hydroxyl (—OH) stretching vibration range given in Table A.1; the area under the curve from 3502cm⁻¹ to 3150cm⁻¹ is shaded, indicating the range of peak area measurement by the above technique.
  • A.2.2 Soot: soot is measured by the baseline shift at 2000cm⁻¹; high concentrations of soot (solid particles with a mass fraction of about 10%) may interfere with the measurement of water in diesel engine crankcase oil, but interference exceeding the soot limit (solid particles of 3% to 5%) has not been encountered so far.
  • A.2.3 Oxidation, nitration, and sulfonation: the oxidation, nitration, and sulfonation degradation products in crankcase oil cannot be quantitatively calibrated with pure standard samples, because different types of oxides and nitrates are continuously generated and accumulated in the oil.
  • A.2.4 Fuel contamination: by measuring the absorption peak at 810cm⁻¹, the possibility of fuel contamination in diesel crankcase oil is judged; it has been found that the spectral characteristics of diesel are different from those of other fuels in Table A.1; other diesel infrared spectral measurement regions and techniques are currently being actively studied; relevant tests, such as viscosity change, flash point, or gas chromatography analysis, can be used to verify the presence of fuel oil measured by FT-IR.
  • A.2.5 Glycol antifreeze contamination: monitor glycol contamination in diesel engine crankcase oil through the stretching vibration of C—O; since glycol also contains hydroxyl groups, its presence will interfere with the accurate quantification of water; the reverse is not true, because glycol also has other spectral features for measurement and quantification; when glycol is present, water can be detected but cannot be accurately quantified using FT-IR.
  • A.3 Extreme pressure anti-wear fluids (typical gear oils or hydraulic oils): the most commonly used parameters are water contamination and oxidative degradation of the oil.
  • A.3.2 Water: unlike the measurement of water in crankcase oil, water is also the most common contaminant in gear oils and hydraulic system lubricating oils; in these systems, water interacts with extreme pressure anti-wear agents to produce different infrared responses; water contamination in extreme pressure anti-wear fluids generally manifests as a horizontal baseline shift across the entire infrared spectrum; when this method becomes the primary measurement method for water in extreme pressure anti-wear agents, water greater than 2% will produce a band similar to the —OH stretching vibration of crankcase oil.
  • A.3.3 Oxidation: Figure A.8 shows the measurement of oxidative degradation of petroleum extreme pressure anti-wear fluids; although Figure A.8 also shows an increase in sulfonation products, not all extreme pressure anti-wear fluids can show this result.
  • A.4 Aviation turbine oils: condition monitoring of high-performance aviation turbine engines is widely used in the military and commercial aviation maintenance industry; the main lubricating oils are synthetic lubricating oils; Table A.3 lists the expected condition monitoring components measured by FT-IR and the ranges of measured band areas and baseline points.
  • A.4.2 Water: different water measurement regions are also necessary for ester-based lubricating oils; the hydroxyl absorption in ester-based oils is at 3700cm⁻¹ to 3600cm⁻¹ (the hydroxyl absorption range in crankcase lubricating oils is 3500cm⁻¹ to 3150cm⁻¹).
  • A.4.3 Ester-based base oil degradation I: the main degradation mechanism of ester-based lubricating oils is the conversion of esters to acids and alcohols; the ester degradation products produced by ester-based base oil degradation I are first in the range of 3595cm⁻¹ to 3500cm⁻¹; the second region of ester-based base oil degradation II associated with the traditional —OH stretching vibration (used as the water measurement region in crankcase lubricating oils) also increases as the lubricating oil degrades.
  • A.4.4 Anti-wear components: the anti-wear components used in petroleum lubricating oils and ester-based lubricating oils in crankcases are not completely the same, but the commonly used anti-wear components in both lubricating oils contain phosphate groups; establishing ZDDP concentration measurement and trend analysis is equally effective for monitoring tricresyl phosphate (TCP).
  • A.4.5 Fuel contamination: determine fuel contamination of ester-based lubricating oils by monitoring the absorption peak at 810cm⁻¹, see clause A.2.4.
  • A.4.6 Other liquid contamination: in addition to fuel contamination, foreign oils and hydraulic oils may also contaminate the lubricating oil (for example, ester-based oil contaminated by petroleum); the measurement regions are listed in Table A.3.
• Appendix B (Normative Appendix) Measurement of Molecular Parameters—Spectral Subtraction:
  • B.1 This appendix is not applicable to all lubricating oils; it is recommended for parameter measurement of petroleum-based lubricating oils; when data become available, other types of lubricating oils can also be added to this appendix.
  • B.1.1 Reference spectra retrieved from spectral libraries cannot be used for spectral subtraction; doing so will produce erroneous results, especially for antifreeze, fuel, and water; if the type of lubricating oil is unknown, it is best to choose the same type of lubricating oil for spectral subtraction; if a suitable reference oil cannot be obtained, spectral subtraction cannot be performed.
  • B.2 Petroleum crankcase oil: the spectral subtraction analysis parameters are similar to those of the direct trend; different laboratories have slight differences in analysis; these different methods are equally effective for trend analysis, with different numerical results; consistency analysis should be applied to each program.
  • B.2.1 Water: water has two characteristic infrared absorptions (3400cm⁻¹ and 1640cm⁻¹), and can be detected at a content of approximately 0.05% to 0.1%; water is measured using a single-point baseline at 3700cm⁻¹ to measure the peak height at 3428cm⁻¹, or using a two-point baseline from 3740cm⁻¹ to 3120cm⁻¹ to measure the maximum value of water; the calibration for water is usually from 0.05% to 2.5%, but can also be as high as 10%; beyond this point, the measurement of water in lubricating oil by this method becomes nonlinear.
  • B.2.2 Soot: Soot particles are the result of incomplete fuel combustion and are only considered in diesel engines; although soot has no specific absorption frequency in the infrared spectrum, light scattering and absorption can also cause baseline shifts in the infrared spectrum; in the region of 1950cm⁻¹ there are no other spectral features, so this region is used to measure soot contamination; the absorbance of soot should be measured before subtracting the reference oil spectrum; the baseline shift caused by soot is affected by the amount of soot and the effective particle size; the effective particle size of soot is measured by the type of combustion system and the dispersant in the oil.
  • B.2.3 Oxidation (carbonyl oxidation products): The broad absorption peak centered at 1730cm⁻¹ is produced by carbonyl groups from lubricant degradation products; these degradation products have been identified as lactones, esters, aldehydes, ketones, carboxylic acids, and salts; the baseline for carbonyl measurement of oxidation value uses 1950cm⁻¹, measuring the highest peak between 1800cm⁻¹ and 1650cm⁻¹; in addition, some laboratories measure the absorbance of the peak near 1709cm⁻¹, with a relative single-point baseline at 1900cm⁻¹.
  • B.2.4 Nitrogen oxidation products: The sharp characteristic peak near 1630cm⁻¹ is produced by fixed nitrogen oxidation value entering the lubricating oil; this substance is nitrate esters; the measurement of the nitrogen oxidation value characteristic is to select the maximum absorption peak in the range of 1650cm⁻¹ to 1610cm⁻¹, using a single-point baseline at 1950cm⁻¹ or 1900cm⁻¹; the formation of fixed nitrogen products mainly exists in gasoline and natural gas engines and diesel engine systems using exhaust gas recirculation.
  • B.2.5 Sulfur oxides: Another broad absorption peak near 1150cm⁻¹ is sulfonates and overlapping peaks with oxides (carboxylates); 1950cm⁻¹ is used as the baseline point; sulfonation products are produced by sulfur entering during diesel fuel combustion or by oxidation of sulfur in base oils and additives in gasoline and natural gas engines; this band is a specific measurement correlated with additive depletion in engine oil and TBN analysis results.
  • B.2.6 Consumption of phosphate anti-wear agents: Monitoring the consumption of phosphate anti-wear agents (represented by zinc dithiophosphate) can indicate abnormal wear or severe operating conditions; additive consumption will become the starting point for accelerated aging of lubricating oil, and monitoring its trend is an indicator for determining lubricant service life; in spectral subtraction, it is measured as a negative peak because new oil contains a higher concentration of such additives than used oil; measure the maximum negative peak in the region of 1020cm⁻¹ to 930cm⁻¹ and use baseline points in the same range.
  • B.2.7 Fuel residue: Measurement of fuel residue or raw fuel is very difficult by any method; the main differences between fuel and base oil are relative molecular mass, boiling range, and relative percentage of aromatics; fuel has a lower boiling point and higher aromatic percentage; conventional methods such as gas chromatography and flash point use low boiling point to measure fuel residue; while infrared methods measure aromatic content to determine fuel residue; the aromatic characteristic band in the range of 817cm⁻¹ to 804cm⁻¹ is used to measure fuel residue; preparation of diesel fuel: representative aged fuel, diesel fuel must be heated to about 107°C and maintained for 30min, about 5% of the original volume; gasoline is heated at low temperature until about 40% of the original volume; gasoline uses the peak area of 734cm⁻¹ to 721cm⁻¹; other related tests, such as viscosity change, flash point, or gas chromatography, can be used to verify the presence of fuel oil predicted by FT-IR.
  • B.2.8 Ethylene glycol: Ethylene glycol contaminants have characteristic absorption in the infrared spectrum, and its detection can reach about 0.1%; ethylene glycol has the same broad hydroxyl peak, centered at 3400cm⁻¹, generally considered to be water absorption; but ethylene glycol also has other characteristic peaks different from water, near 1080cm⁻¹ and 1040cm⁻¹; the peak height at 883cm⁻¹, with a single-point baseline at 917cm⁻¹, is used to quantify ethylene glycol because it is not interfered with like 1040cm⁻¹ and 1080cm⁻¹; a large number of sulfonate bands form a shoulder peak with the ethylene glycol peak on the right side; even if 1040cm⁻¹ and 1080cm⁻¹ are higher than the 880cm⁻¹ peak, accurately measuring them in the presence of other lubricant degradation products is very difficult; but the peaks at 1040cm⁻¹ and 1080cm⁻¹ can be used to determine the presence of ethylene glycol; second derivative spectra can accurately determine the exact positions of these peaks; as the ethylene glycol mass fraction increases from 0.05% to 0.08% concentration, its absorption intensity also increases; when ethylene glycol is present, water can be detected but cannot be accurately quantified using FT-IR; the presence of ethylene glycol can also be determined by gas chromatography, colorimetric tests, or other common methods, and confirmed by elemental analysis results for sodium and boron.
  • B.2.9 Data reporting: Some components are not calibrated, including oxidation value, nitration value, sulfonation value, soot, and phosphate anti-wear additives; other calibrated components include diesel fuel, gasoline, water, and ethylene glycol.
  • B.2.9.1 Oxidation value, nitration value, and sulfonation value components do not report their concentration values because the various compounds produced all have absorption, the products formed are not single, and standard substances cannot be used for calibration curves relating concentration to absorbance; the unit used in the report is absorbance per 0.100mm (Abs/0.100mm).
  • B.2.9.2 Soot results are also reported as absorbance value per 0.100mm (Abs/0.100mm).
  • B.2.9.3 Phosphate anti-wear additives: reported as 0.100mm absorbance (Abs/0.100mm); however, anti-wear additives are reported as negative values because they are continuously consumed compared to the original reference oil, making the spectral subtraction value between the used lubricating oil and the reference oil negative.
  • B.2.9.4 Fuel, water, ethylene glycol, and gasoline are expressed as weight percentages when calibrated with standard samples; calibration for diesel and gasoline fuels may not use in-use fuels that accurately represent a specific region of the world; these components should be calibrated with locally obtained aged fuel samples; water and ethylene glycol are usually very consistent because their chemical composition usually does not change, only the percentage of ethylene glycol in the antifreeze mixture varies; these components do not need frequent local calibration because standard sample preparation and analysis are relatively difficult.
  • B.2.9.5 In practice, the method using absorbance measurements of non-calibrated components is to record their increase with operating time in the engine; from the graph or table of absorbance and time changes, the time to change the lubricating oil can be determined.
• Appendix C (Normative Appendix) Distribution charts and statistical analysis:
  • C.1 Statistical analysis of historical data from a large number of mechanical equipment can be used to explore possible relationships between condition monitoring test data and mechanical equipment failure modes; this statistical analysis is a tool used to determine alarm limits for condition monitoring tests.
  • C.2 Frequency distribution chart—histogram: A distribution chart is a common tool used for statistical analysis of condition monitoring data; the horizontal axis of the chart is the sample test results, and the vertical axis is the frequency of occurrence of the exact results of all test samples.
  • C.2.2 To establish reliable alarm limits from statistical analysis of condition monitoring test data, the data must be approximately normally distributed; the histogram should approximate a bell shape and have no multimodal characteristics.
  • C.2.3 When infrared spectroscopy results are limited to non-true and the distribution centerline is close to zero, the distribution will appear abnormal; although the mean and standard deviation can be calculated, users should verify the alarm limits based on the description of the actual distribution of the statistical data.
  • C.2.4 Multimodal, flat distributions should not be used for statistical analysis; both examples indicate very low failure data or poor measurement precision data for the same data.
  • C.3 Sampling note: Statistical analysis should include historical data from all mechanical equipment of the same type, at least covering one overhaul period; for meaningful statistical analysis, at least several hundred results are needed; if the number of mechanical equipment is large, less than one maintenance cycle may be sufficient; unless there is a special analysis statement, results from different models of mechanical equipment and different lubricant formulations should be separated and analyzed individually; even different oil tank sizes or different metal materials of mechanical equipment should first be analyzed separately; randomly selected samples do not necessarily produce the specified normal distribution results, and continuous sampling throughout the entire overhaul period is more likely to produce normally distributed results; the overall analysis must include typical failures, including examples of lubricant-related failure modes; if too many failure samples are included, the distribution may be wide and the calculated limits may be too high; conversely, if the representative number of failure modes is too small, the distribution may be narrow and the calculated limits may be too low.
  • C.4 Test alarm limit calculation: The specific calculation limits in the procedure are determined by the recommendations and guidance of mechanical equipment manufacturers and maintenance organizations; the user first selects the test level and the type of alarm; usually warning or alert levels will be used as an initial indication of potential problems, and distinction will be used for indicators requiring immediate maintenance action; higher alarm levels can be used, but increase complexity; mark the lubricant test result data in the histogram, marking lubricant-related failure data; verify that the frequency distribution is approximately normal; calculate the tentative limits based on the mean and standard deviation of the lubricant test results; the mean plus two standard deviations calculates the tentative alarm (warning) limit; this assumes results where values increase with time; for results where values decrease with time, the limit will be the mean minus the corresponding standard deviation; the mean plus four standard deviations calculates the tentative alarm limit.
• Appendix D (Informative Appendix) Scattering phenomena in infrared liquid transmission sample cells:
  • D.1 When light passes from one material into another, its speed changes due to the change in refractive index; unless the refractive index is exactly matched, the amount of light transmitted through the medium surface is less than 100% because part of the light is reflected; if light passes through a thin film material, such as a polymer film, two such interfaces meet and reflection may occur; the result of this internal multiple reflection is an increase in the optical path length of radiation inside the film, and thus a phase delay of the light transmission from the original beam; this causes mutual interference (weak) of the two beams; this interference is determined by wavelength, resulting in a wavenumber spectrum showing a regular superimposed sine wave on the baseline.
  • D.2 This interference phenomenon can also be seen when using liquid transmission cells, because the air gap between the two windows produces the same interference effect as the polymer film described above; this optical effect can be measured by spectral fringes on the interferogram or the observed phase delay to measure the thickness of the empty sample cell; in the case of using salt windows, when the oil sample enters the sample cell, very weak interference fringes are produced because the reflectivity of the salt window is relatively close to the oil sample, so the interference fringes in the spectrum basically disappear; if ZnSe windows are used, when the oil sample is introduced into the sample cell, strong interference fringes can still be seen because the refractive index of ZnSe is much larger than that of the oil sample; if the background spectrum is collected using an empty sample cell, or the sample spectrum is collected using a ZnSe sample cell with completely parallel windows, these interference fringes will appear in the oil absorption spectrum; using interference fringe processing techniques can avoid these problems; the conventional method is to use computer operations to remove the sample, clean the sample cell, collect the background, and find the second (phase lag) center point on the recorded interferogram; the converted single-beam spectrum therefore shows only minimal interference fringes; techniques based on computer fitting or elimination of regular sine waves, using sample cells with anti-reflection coated windows, or using wedge-shaped window sample cells (less than 0.5° change) have been used to reduce the scattering effect of the spectrum.

9. Qualitative and quantitative and calculation formulas

• 9.4 Data processing: all spectra are expressed as a function of absorbance corresponding to wavenumber; before reporting, the calculated data must be corrected with reference to the 0.100mm optical path to address optical path differences among commercial sample cells.
• 9.4.1 Direct trend: through the spectral data processing results, the spectral change trend of the in-service lubricating oil can be directly obtained (direct trend); the best spectral data processing is spectral correction or correction with reference to the 0.100mm reference optical path, and if necessary, an interference fringe reduction algorithm for the spectrum may also be applied.
• 9.4.2 Spectral subtraction: the difference spectrum produced by subtracting the new oil reference spectrum from the in-service lubricating oil spectrum; the spectra of the in-service lubricating oil and the new oil reference must be corrected with reference to the 0.100mm optical path before spectral subtraction, and a subtraction factor of 1:1 should be used; the spectral subtraction result can obtain the trend of the in-service lubricating oil changing with operating time, and is processed in a manner similar to the direct trend method of infrared spectroscopy.
• 9.4.3 Final analytical data processing may also use multiplication and other scaling techniques; for example, to facilitate evaluation and expression by maintenance personnel, "value ×100" may be used (see Appendix A).
• Table A.1 Petroleum-based lubricating oil (e.g., crankcase oil) condition monitoring parameters (direct trend method):
  • Water: measurement area 3500～3150cm⁻¹; baseline points 4000～3680 and 2200～1900 minimum absorption wavelength points; reported value (Abs/0.100mm) measured value ×100
  • Soot: absorption intensity at 2000cm⁻¹; baseline points 2200～1900 and 650～550 minimum absorption wavelength points; reported value measured value
  • Oxidation value: measurement area 1800～1670cm⁻¹; baseline points 2200～1900 and 650～550 minimum absorption wavelength points; reported value measured value
  • Nitration value: measurement area 1650～1600cm⁻¹; baseline points 2200～1900 and 650～550 minimum absorption wavelength points; reported value measured value
  • Anti-wear component (phosphate, commonly ZDDP): measurement area 1025～960cm⁻¹; baseline points 2200～1900 and 650～550 minimum absorption wavelength points; reported value measured value
  • Gasoline: measurement area 755～745cm⁻¹; baseline points 2200～1900 and 650～550 minimum absorption wavelength points; reported value measured value
  • Diesel (JP-5, JP-8): measurement area 835～825 and 805～795cm⁻¹; baseline points 2200～1900 and 650～550 minimum absorption wavelength points; reported value (value + 2) ×100
  • Sulfonation value type products: measurement area 1130～1100 and 1030～1010cm⁻¹; baseline points 2200～1900 and 650～550 minimum absorption wavelength points; reported value measured value
  • Ethylene glycol coolant: measurement area 780～760 and 750～730cm⁻¹; baseline points 2200～1900 and 650～550 minimum absorption wavelength points; reported value measured value
  • Note: the unit of the reported value is Abs/0.100mm (see 6.1.2)
  • Note: the spectral characteristics of diesel and other commonly used fuels differ, and other infrared measurement regions and techniques are currently under study; the listed measurements can serve as an indicator, but will not become the only infrared measurement method for fuel contamination; check the source of suspicious fuel, and it is recommended to verify the presence of absorption bands.
• Table A.2 Petroleum-based extreme pressure anti-wear fluid condition monitoring parameters—direct trend:
  • Water: measurement area 3400～3250cm⁻¹; baseline points no baseline; reported value (Abs/0.100mm) measured value ×20
  • Oxidation value: measurement area 1800～1670cm⁻¹; baseline point 2200