Fluids Analysis

Laboratory Guide

SEBF3117-01 (6/93)

Infrared Analysis By Differential Scan

Table of Contents Introduction ................................................... 1 Dispersive Infrared Analysis .......................... 2 The Infrared Scan .......................................... 3 Reading the Scan .......................................... 4 Contaminants and Their Identification ........... 7

1. Water .................................................... 7 2. Ethylene Glycol ..................................... 8 3. Water and Ethylene Glycol Mixture ....... 8 4. Soot ...................................................... 8 5. Oxidation .............................................. 9

Oxidation in Diesel Engines ................. 10 Oxidation in Natural Gas Engines ........ 10 Oxidation in Hydraulic System ............. 10 Oxidation in Transmissions ................. 11

6. Sulfur Products ................................... 11 7. Nitration .............................................. 11 8. Hydraulic Oil Decomposition ............... 12

Interpretation ............................................... 13 Applications of Interpretation Basics ............ 13 Maximum Safe Limits .................................. 13 Sample Analysis .......................................... 15

1. Sample Preparation ............................ 15 2. Filling the Cell ..................................... 15 3. Cleaning the Cell ................................ 16 4. Running a Sample .............................. 16

Fourier Transform Infrared Analysis ............ 17 Glossary of FTIR Terms .............................. 18 FTIR File Organization ................................ 19 FTIR Operational Guidelines ....................... 19 Results ........................................................ 20 Evaluation of Results ................................... 21 Autoreference .............................................. 21

Introduction Dispersive infrared analysis (DIR) is a diagnostic test added to the S·O·S program in 1979. Generally called infrared analysis (IR), this test determines the degree of used oil deterioration by measuring soot, oxidation, nitration and sulfur products. It can indicate additive loss, and detect oil contamination from water and antifreeze (i.e., ethylene glycol). Fourier Transform infrared analysis (FTIR), introduced in 1987, is more reliable than the DIR. The FTIR can detect diesel fuel dilution of the oil and is more reliable in detecting the presence of contaminants (fuel, water, glycol). The FTIR and DIR techniques utilize the same principles for spectrum interpretation. However, FTIR is more sensitive than DIR allowing quantitative measurement of water, glycol, and fuel. Both the DIR and FTIR techniques analyze the sample by comparing the used oil with the new oil reference and evaluating the difference. This is called a differential infrared analysis. The reference oil is a key part of the analysis. Using the wrong reference oil may produce erroneous results. CONFIDENCE IN THE RESULTS IS DIRECTLY RELATED TO USING THE CORRECT REFERENCE OIL IN THE ANALYSIS.

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Infrared analysis MAY help indicate whether the new oil is the same as another and it MAY verify that a new supply of oil is the same formulation as the previous shipment. Infrared analysis CANNOT determine whether an oil meets API or SAE classifications; it CANNOT determine the oil’s viscosity nor identify a multi-viscosity oil; and it CANNOT measure total base number (TBN) directly. INFRARED ANALYSIS, LIKE OTHER FLUID ANALYSIS, SHOULD NEVER BE USED ALONE. Use it in conjunction with wear metal analysis, particle count, chemical and physical tests to ensure accurate interpretations and recommendations. By monitoring the used oil condition, a more thorough indication of a failure and its cause may be identified. Infrared analysis answers some of the questions raised by wear metal analysis alone (e.g., cause for bearing wear, ring sticking, transmission slippage, etc.). Interpretations can be improved when infrared analysis is used as a diagnostic tool to help identify problems and their causes. Best results are obtained by performing infrared analysis on each sample and using trend analysis techniques. A deviation from the normal trend can signal problems before the maximum allowable limits are exceeded. Typically, the dispersive infrared scan was not completed on all oil samples because of time and resource constraints in the lab. Caterpillar evaluated infrared instrumentation suppliers and chose Nicolet Analytical Instruments to develop the FTIR oil analysis technique. The resulting Nicolet Model 8210 Oil Analyzer simply and quickly performs FTIR used oil analysis.

This bulletin provides instructions for performing infrared analysis (IR) of used oil with either dispersive infrared analysis (DIR) or Fourier Transform Infrared analysis (FTIR). The logic of the DIR technique will be examined first in the bulletin, and an explanation of FTIR will follow and build on the DIR principles explained.

Dispersive Infrared Analysis The DIR was the first infrared technique used by the Caterpillar S·O·S program. This technique requires more time for analysis and results must be calculated by evaluating graphical output.

NOTICE Two types of chart paper are available to record the differential scan, transmittance and absorbance. Caterpillar’s application uses absorbance paper which has a logarithmic ordinate scale allowing measurements to be read directly.

Caterpillar recommends all engine, transmission, and hydraulic oil samples receive infrared analysis. Often, resource limitations will not permit this recommendation to be fulfilled with DIR equipment. When only DIR equipment is available, an analysis performed at the time of machine enrollment in the S·O·S program will establish an IR initial reference which can then be used as a basis of comparison. In this case, the reference must be re-established each time the brand or type of oil changes. Infrared analysis should be performed on all samples which have unacceptable readings from the wear metal and/or chemical and physical tests.

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The Infrared Scan There are two types of infrared scans, direct and differential. This bulletin discusses the differential scan which is easier to interpret with the DIR technique. The differential scan graphs the difference between the new oil (oil before it is placed into the machine at oil change interval) and the used (sample) oil. Because the new oil is used as the reference oil, it is important that it is the same grade, brand and formulation as the used oil sample. If the oils are not the same formula, a valid scan cannot be obtained. Therefore, the customer must provide the lab with a new oil sample each time he changes brands, suppliers or receives a new bulk shipment. A differential scan, using both new and used oil, charts the differences between the oils. A deflection, or peak, at a specific known wavelength or wavenumber (WN) on the scan indicates a contaminant is present. (The terms “deflection” and “peak” will be used interchangeably throughout this bulletin. Positive contaminant identification generally requires an indication at more than one wave number (WN). Sometimes this identification cannot be made because of interferences from other contaminants. The wavenumbers (WN) are broken into two groups. WN 4000 to 2000 is the “functional group”; WN 2000 to 650 is the “fingerprint group”. The functional group indicates the presence of one or more contaminants. The fingerprint group identifies the specific contaminant.

The following chart identifies contaminants of concern, their wave number (WN), and limits:

Contaminant Functional Fingerprint Limits Water WN 3400 WN 1630 Presence

Detected Ethylene Glycol

WN 3300 WN 1075 & 1030

Presence Detected

Fuel — — Presence Detected

Oxidation — WN1710 & 1630

%Allowable

Nitration — WN 1630, 1560,

1270 & 860

% Allowable

Sulfur Products

— WN 1150 % Allowable

Soot — WN 2000 % Allowable

NOTICE Soot is determined by reading the percent transmittance of a sample at WN 2000 with DIR analysis. Refer to the Sample Analysis section in this bulletin for detailed procedural information.

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Reading the Scan The top and bottom of the chart paper in Illustration 1 displays two different sets of numbers. The top set refers to the wave length in micrometers. The bottom set, which we use, refers to wave numbers (WN) in reciprocal centimeters (cm 1).

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Between major ordinates there are 0.1 absorbance units. Between ordinates 0.0 and 0.1, 0.1 and 0.2, and 0.2 and 0.3, there are ten boxes. Each box equals 0.01 absorbance units. Between 0.3 and 0.4, 0.4 and 0.5, 0.5 and 0.6, 0.6 and 0.7, and 0.7 and 0.8, there are five boxes. Each box equals 0.02 absorbance units. Between ordinates 0.8 and 0.9, and 0.9 and 1.0, there is only one box. Each box equals 0.10 absorbance units.

A baseline is used as a dividing line to determine whether the scan information originates from the reference oil or the sample oil. The baseline depicts the general slope of the scan. If the sample oil and reference oil are both new oils and a DIR analysis is performed, the new oil scan normally has a horizontal slope (Illustration 2). This is also true for a scan of low sooted oil. The scan of highly sooted oil shows a sloping base line (Illustration 3). The higher the amount of soot in the oil, the greater the baseline slopes.

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A baseline is drawn on the spectrum that best diesel engine, it is defined as the straight line that connects WN 4000 and 1800. There are instances (such as natural gas engines) where this may not be true. In these instances, a “consistently” best fit base line may be used. When looking at a scan after a base line has been drawn, everything above the base line is indicative of the reference oil. The portion below the base line is indicative of the sample oil. Deflections above the baseline indicate that the reference oil contains a contaminant or additive which is either in greater quantity or is not

contained in the sample oil. Deflections below the baseline indicate that the sample contains a contaminant or additive which is either in greater quantity or is not contained in the reference oil.

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For example: As oil is used, it begins to break down. The breakdown may be indicated by additive decomposition. In looking at a differential scan of an oil with high additive decomposition (depending on which additive), a peak may be seen above the base line. This is because the reference oil additive package has not decomposed and would have the additive in greater quantities than the sample oil. A cooling system leak allowing coolant into the oil, would deflect below the base line on an IR scan because the sample oil would contain coolant and the reference oil would not. The quantity of a contaminant is determined by the depth of the deflection from the base line. The depth is read in absorbance units.

The calculation of absorbance units, counting down from the base line, and assigning proper absorbance values are shown in Illustration 3.

Contaminants and Their Identification Contaminants result from outside sources or from chemical changes in the oil. Contaminants such as fuel, water, ethylene glycol, and soot are from outside sources. Oxidation and nitration are from chemical changes in the oil. Sulfur products are also from a chemical change, but are created from normal contamination during the diesel engines combustion process. The following list discusses the identification of contaminants. Sample scans are included.

Water is detected at WN 3400 in the functional group and at WN 1630 in the fingerprint group. Normally, there are also deflections at WN 1200 and 1050. These deflections indicate the new compounds which are formed when oil

additives combine with water. Also see the section titled Sulfur Products in this bulletin. If water were the only contaminant mixed with mineral oil, only defections at WN 3400 and 1630 would be indicated. Water flashes into steam when it contacts a hot surface causing oil film reduction on that surface. This accelerates wear.

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Water and oil react causing sludge (gel) and acid formation. The gel may cause filter plugging and lead to other problems. This gel could contain up to 95% water. If the oil temperature becomes high enough, the water in the gels thins out and dissipates back into the oil. When the oil temperature decreases, the gel will form again.

2. Ethylene Glycol Illustration 4 Ethylene glycol is present at WN 3300 in the functional group and at WN 1075 and 1030 in the fingerprint group. Note that in high concentrations, it is also present at WN 860. No method has yet been found to distinguish between the glycol compounds used in the oil formulation process and ethylene glycol contamination. Contamination from ethylene glycol causes the oil to thicken. The sludge may cause the filter to plug and lead to other problems. Ethylene glycol acts as a catalyst speeding up oxidation. Also see the section titled Oxidation in this bulletin.

3. Water and Ethylene Glycol Mixture The spectrum of a 50/50 mixture of water and ethylene glycol standard at a 1% concentration in new oil would show the mixture combining to form a single deflection at the intermediate frequency of WN 3375 in the functional group. In the fingerprint group, water is detected at WN 1630, glycol at WN 1075 and 1030.

4. Soot Soot is measured by reading the transmittance at WN 2000 and converting to percent allowable. The WN 2000 was selected as the location for soot determination since this area is relatively free of absorbance from other products. Therefore, a valid

amount of light throughput can be obtained. Refer to the section titled Sample Analysis in this bulletin for test procedure details. The soot index indicates suspended solids in the oil. Soot particles produced by a diesel engine are approximately 0.025 micrometers (microns) in size. Though these particles form clusters to some degree, they remain too small to be filtered as long as sufficient dispersants are present. The soot particles circulating in engine oil may represent several times the capacity of the oil filter. As long as the soot particles are dispersed, they remain in suspension and cause little harmful effects. When the dispersant breaks down, soot particles agglomerate to form abrasive clusters and/or plug filters. If the wear metal readings rise at an accelerated rate with the soot reading, shorten oil change intervals. Soot is determined by the % transmittance at WN 2000. As the % decreases, the soot index increases. In other words, low % transmittance (less light passed through the sample) means a greater amount of soot in the oil. Soot is influenced by the following: • Rack setting • Air fuel ratio control • Fuel nozzle operation • Turbocharger operation • Air cleaner operation • Crankcase blowby • Timing • Engine operation (i.e., rapid acceleration,

lugging)

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The most commonly understood form of oxidation is rusting - oxygen combining with iron. As with iron, oil oxidizes when oxygen joins the oil molecule. Oxidation is accelerated by high temperature, contaminants, and constant agitation. The rate of oxidation doubles with each 10°C (18°F) increase in temperature. Certain metals, especially copper, act as catalysts to speed up the oxidation process. As oil oxidizes, it loses its lubricating properties and forms resins. The most noticeable change is a thickening of the oil.

The most pronounced oxidation deflections occur at WN 1720 and 1630. Oxidation is measured at WN 1720. In some instances, a wide band occurs between WN 1700 and 1750 with only a small shoulder in the deflection at WN 1720. While oxidation is still measured at WN 1720, the deflections at other frequencies should be noted if they are larger. An interference sometimes found at WN 1720 is a viscosity index improver commonly used in multiviscosity oils. Loss of this additive reduces the deflection depth for oxidation. The degree of oxidation is expressed in units of absorbance and then reported as % allowable. Absorbance is obtained by subtracting the lowest point in the deflection from the base line.

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Oxidation is increased by: • High temperature • Exposure to air and/or air (oxygen)

entrainment • Catalysts such as ethylene glycol or copper • Time oil is in use (extended oil change period) Oxidation products can increase viscosity and cause filter plugging. When oxidation becomes the limiting factor (as defined by an accelerated rise in wear metals), the maximum oil life has been realized.

Oxidation in Diesel Engines The rate of oxidation in diesel engines depends on the length of time the oil is in use, engine temperature, ethylene glycol contamination, sulfur products and anti-oxidant additives present in the oil. Oxidizing agents in combustion gases accelerate oxidation. Ethylene glycol contamination (not glycol formulation compounds) may cause a rapid oxidation rate in the diesel engine. Oxidation seen at WN 1720 frequently causes varnish formation and piston ring sticking.

Oxidation is the main cause of oil deterioration in Caterpillar turbocharged natural gas engines. Its causes and effects are the same as those in diesel engines. When oxidation is greater than nitration, overheating is indicated or the engine is operating close to the rated load. Excessive oxidation may be seen by a deflection at WN 3450. Other reaction products may also be seen at WN 1165.

Oxidation in the Hydraulic System The oxidation rate in the hydraulic system depends on exposure to oxygen (air), length of time oil is in use, temperature, the inhibiting effect of anti-oxidant additives, and the catalytic effect of contaminants such as copper, iron or ethylene glycol. Excessive oxidation measured at WN 1720 before the regular oil change period usually indicates overheating. Overheating may be general or due to local hot spots. Samples showing oxidation in the hydraulic system

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should be trended for best results, but 0.05 absorbance units or above of oxidation should be cause for investigation.

Oxidation in Transmissions Oxidation in the transmission depends on exposure to air, time, temperature, oxidation inhibitors in the oil and the catalytic effect of contaminants such as copper, iron or ethylene glycol. Excessive oxidation measured at WN 1720 before the regular oil change period, usually indicates overheating. Overheating may be due to clutch slippage, cooler plugging, or a combination of the two. Oxidation results in the transmission should be trended for best results, but 0.05 absorbance units or above of oxidation should be cause for investigation.

6. Sulfur Products Illustration 5 Sulfur products are a by-product of combustion caused by sulfur in diesel fuel and are indicated by a broad band deflection at WN 1150. Sulfur products can combine with water in the oil (from condensation, leaks etc.) to form sulfuric acid. The sulfuric acid causes corrosion and may lead to pitting of engine components.

Total base number (TBN) is a measure of an oil’s ability to neutralize acid. High sulfur products may indicate a need to monitor the depletion of the oil’s TBN and to check the percent of sulfur in the fuel.

Illustration 5 shows a peak resulting from sulfur products. Sulfur products are measured in units of absorbance.

Sulfur product formation varies with:

• Sulfur content of fuel • Crankcase blowby • Crankcase capacity • Operating conditions • Oil formulation • Temperature • Air humidity • Oil change interval

7. Nitration Illustration 6 Although nitration occurs in all engines, it is a major consideration only in natural gas engines. The process begins in the combustion chamber where nitrogen oxides form from heat and pressure. Further reaction with fuel and oil results in nitrogen compound accumulations in the oil. These compounds cause deposits and thickening that interferes with lubrication. Nitration is accelerated in engines with excessively lean air/fuel ratios and improper ignition timing. Lean air/fuel ratios can retard nitration in light load applications.

Nitration is observed on the IR scan at WN 1630 and deflections at WN 1270 and 860. Excessive blowby may be monitored by a deflection at WN 1560.

Blowby should be reduced as much as possible. Checking the crankcase breather for proper operation at each oil change may be necessary.

The level of nitration is measured by the depth of deflection from the base line at WN 1630 and is expressed in units of absorbance.

Nitration is influenced by: • Incorrect air/fuel ratios • Improper spark timing in spark ignited engines • High loads • Low operating temperatures • Crankcase blowby • Crankcase capacity • Tendency of different oils to allow formation of

nitro-compounds • Oil change interval

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Zinc Dithiophosphate (ZDTP) is the chemical composition of most concern in the hydraulic system. It is primarily an anti-wear additive, but it also functions as an anti-oxidant. The anti-wear additive is necessary to protect hydraulic pumps (especially vane-type pumps) and it achieves this by chemically bonding with the rubbing surface. Depletion by chemical bonding is not a factor during the change period due to the relatively large amount of oil in a Caterpillar hydraulic system compared to the rubbing surfaces area.

The major cause of anti-wear additive loss is thermal decomposition caused by localized areas of heat. The decomposition products include hydrogen sulfide (H2S) which can often be detected by its “rotten egg” smell. The loss of the Zinc Dithiophosphate additives can be detected by differential infrared spectroscopy at WN 920, 980 or 1000.

Thermal decomposition is further characterized by peaks at WN 1140, 1180, 1330 and 1350. These peaks are the result of decomposition and oxidation products at WN 1720 and 1690. When there is evidence of thermal decomposition, the oil and filter should be changed and the “hot spot” found and corrected.

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INFRARED INTERPRETATION WAVENUMBER IDENTIFICATION CHART

WAVENUMBER ITEM 3450 EXCESSIVE OXIDATION 3400 WATER 3375 WATER & ETHYLENE GLYCOL 3300 ETHYLENE GLYCOL 3000-2800 AIR BUBBLE OR DIFFERENT CELL

THICKNESS (TRANSMISSION CELL)

2000 SOOT DETERMINATION 1750 VISCOSITY IMPROVERS 1720 OXIDATION PRODUCTS &/or

VISCOSITY IMPROVERS 1710 OXIDATION PRODUCTS 1690 OXIDATION PRODUCTS 1630 NITRATION, WATER, OXIDATION

PRODUCTS 1560 NITRATION 1500-1400 DETERGENTS/DISPERSANTS 1440 & 1360 AIR BUBBLES 1370 INORGANIC NITRATES (METALLIC

COMPOUNDS) 1350 ZINC DITHIOPHOSPHATE (ZDTP)

DECOMPOSITION PRODUCTS 1330 ZDTP DECOMPOSITION

PRODUCTS 1300-1000 WIDE NITRATION BAND 1300-900 WIDE SULFUR PRODUCTS BAND 1270 NITRATION 1200 VISCOSITY IMPROVERS 1180 ZDTP DECOMPOSITION

PRODUCTS 1165 OXIDATION PRODUCTS 1150 SULFUR PRODUCTS 1140 ZDTP DECOMPOSITION

PRODUCTS 1075 ETHYLENE GLYCOL 1030 ETHYLENE GLYCOL 1000 ZDTP (ANTI-WEAR ADDITIVE) 980 ZDTP 920 ZDTP 860 NITRATION

Interpretation In infrared analysis, as in wear metal analysis, the trend for a machine/component must be established. Caterpillar recommends oil condition be evaluated for each sample to establish a trend and aid in sample diagnosis. It is important that a new base line be set each time the machine’s operating condition, the oil brand or type changes.

As with other fluids lab tests, IR as a test, will not stand alone. All lab test results must be analyzed together to formulate an interpretation. The limits given are general guidelines for Caterpillar-built products only and cannot be applied to competitive equipment. The amount of insolubles, oxidation, nitration and sulfur products which can be tolerated by an engine depends upon the engine design. The same is true of other compartments.

Application of Interpretation Basics The use of infrared analysis to determine a problems source follows a logical process of elimination. Once the peaks and deflections of an IR scan have been identified, both qualitatively and quantitatively, IR results should be interpreted in conjunction with other test results. The analysis of AA, IR and physical test results can help determine the origin of the wear and direct you to the cause.

Maximum Safe Limits A small water leak can be tolerated in an engine at operating temperature. Up to 0.5% water can be absorbed in crankcase oil. The chemistry involved with this oil and water mixture is quite involved. If water content in the oil remains below 0.5% and the recommended oil change periods are followed, no action is required. Any amount of antifreeze in oil is unacceptable. Antifreeze leaking into an engine can cause serious to catastrophic results depending upon the leak’s location. Antifreeze combining with oil can cause bearing damage, filter plugging, gel formation and wear metal increase in the cylinders. Worst case scenario is hydraulic lock.

Contaminants Maximum Safe Limits % Allowable Soot (See Notice) 50% Transmittance 100 Oxidation 0.30 Absorbance Units 100 Sulfur Products 0.30 Absorbance Units 100 Nitration 0.20 Absorbance Units 100 Oxidation in Natural Gas Engines

0.20 Absorbance Units 100

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NOTICE Even though the soot reading may be within the 50% Transmittance, if the wear metal readings rise at an unacceptable rate with the soot reading, the oil change interval should be shortened. (Also refer to Soot in this bulletin.)

The following tables are for converting absorbance units to % allowable:

MAXIMUM SAFE LIMITS - % ALLOWABLE CHART

Diesel Engine Soot Index %

Trans. %

Allowed %

Trans. %

Allowed %

Trans. %

Allowed 100 0 66 68 32 136 99 2 65 70 31 138 98 4 64 72 30 140 97 6 63 74 29 142 96 8 62 76 28 144 95 10 61 78 27 146 94 12 60 80 26 148 93 14 59 82 25 150 92 16 58 84 24 152 91 18 57 86 23 154 90 20 56 88 22 158 89 22 55 90 21 158 88 24 54 92 20 160 87 26 53 94 19 162 86 28 52 96 18 164 85 30 51 98 17 166 84 32 50 100 16 168 83 34 49 102 15 170 82 36 48 104 14 172 81 38 47 106 13 174 80 40 46 108 12 176 79 42 45 110 11 178 78 44 44 112 10 180 77 46 43 114 9 182 76 48 42 116 8 184 75 50 41 118 7 186 74 52 40 120 6 188 73 54 39 122 5 190 72 56 38 122 4 192 71 58 37 126 3 194 70 60 36 128 2 196 69 62 35 130 1 198 68 64 34 132 0 200

MAXIMUM SAFE LIMITS - % ALLOWABLE CHART

Diesel Engine Oxidation, WN 1720

Sulfur Products, WN 1150 Abs. Units % Allowed Abs. Units % Allowed

0.01 3 0.31 103 0.02 7 0.32 107 0.03 10 0.33 110 0.04 13 0.34 113 0.05 17 0.35 117 0.06 20 0.36 120 0.07 23 0.37 123 0.08 27 0.38 127 0.09 30 0.39 130 0.10 33 0.40 133 0.11 37 0.41 137 0.12 40 0.42 140 0.13 43 0.43 143 0.14 47 0.44 147 0.15 50 0.45 50 0.16 53 0.46 153 0.17 57 0.47 157 0.18 60 0.48 160 0.19 63 0.49 163 0.20 67 0.50 167 0.21 70 0.51 170 0.22 73 0.52 173 0.23 77 0.53 177 0.24 80 0.54 180 0.25 83 0.55 183 0.26 87 0.56 187 0.27 90 0.57 190 0.28 93 0.58 193 0.29 97 0.59 197 0.30 100 0.60 200

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MAXIMUM SAFE LIMITS - % OF ALLOWABLE CHART

Natural Gas Engine Oxidation, WN 1720 Nitration, WN 1630

Abs. Units % Allowable Abs. Units % Allowable 0.01 5 0.21 105 0.02 10 0.22 110 0.03 15 0.23 115 0.04 20 0.24 120 0.05 25 0.25 125 0.06 30 0.26 130 0.07 35 0.27 135 0.08 40 0.28 140 0.09 45 0.29 145 0.10 50 0.30 150 0.11 55 0.31 155 0.12 60 0.32 160 0.13 65 0.33 165 0.14 70 0.34 170 0.15 75 0.35 175 0.16 80 0.36 180 0.17 85 0.37 185 0.18 90 0.38 190 0.19 95 0.39 195 0.20 100 0.40 200

Sample Analysis (DIR Method) Follow manufacturer’s recommendations for instrumentation operation. In Caterpillar’s application, the DIR differential scan is recorded on logarithmic chart paper. This allows the scan to be directly interpreted.

NOTICE For information on the operation and calibration of a specific infrared spectrophotometer, refer to the manufacturer’s instructions.

Two IR cells are used to perform the differential scan. One cell holds the sample oil, the other the reference oil.

Two cell types suitable for infrared analysis are the sealed cell and the demountable cell. Sealed cells are permanently assembled with the desired arrangement of spacers and windows (crystals). They provide consistency of film thickness for more uniformity. The demountable cells are easily disassembled and reassembled with the desired spacers and crystals by the lab technician. The optimum spacer thickness is 0.1 mm which gives the same dimension between the two crystals. When in use, either type of cell is used in sets for the purpose of an analysis. The distance between the two crystal plates must be similar for both cells. A procedure for determining the distance between the crystal plates is described in most instrument operation manuals. Various types of crystals are available. Barium fluoride (BaF2) crystals are the most suitable because they are the least affected by deterioration caused by the water present in some oil samples. To keep the cells as dry as possible, store them in a desiccator with anhydrite crystals. Humidity in the air speeds crystal deterioration.

1. Sample Preparation Prior to filling the cells, thoroughly shake the necessary oil samples on a paint shaker for three minutes minimum. This may be done any time earlier in the day. Allow the sample to stand for a minimum of 30 minutes to allow air bubbles to escape. If the sample stands for more than an hour, stir the sample with a glass rod, without ingesting air into the sample, before filling the cell.

2. Filling the Cell When filling the cell, the cell should be at a 30° angle to the countertop. To aid in filling and cleaning cells, an IR cell holder has been designed. Contact Caterpillar for the fabricated tool print, FT1564, which can be used to make the cell holder.

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To fill the cell proceed as follows: 1. Place the clean IR cell in the cell holder. 2. Stir each sample or reference oil with a

clean glass stirring rod to prevent cross contamination.

3. Use the glass stirring rod to transfer three drops of sample or reference oil to the cell’s lower fill port.

4. Inserting a plug in the lower fill hole with slow steady pressure will push the oil up into the crystals. Leave the plug in the port to hold the oil in the cell.

An alternate method would be to attach a vacuum line to the upper fill port and pull the sample up between the crystals. 5. Hold the cell up to the light to check for air

bubbles. If air bubbles are present, clean the cell and repeat the procedure. A white background inserted behind the cell on the cell holder will aid in detecting air bubbles entrained in the sample. If no air bubbles are present, the cell is ready for analysis.

3. Cleaning the Cell Prior to Use Clean the cell by flushing solvent (heptane) through the cell while applying a vacuum. 1. Attach the vacuum to the top port. 2. While applying vacuum, use a wash bottle

to squirt heptane through the lower port. 3. When all oil is flushed from the cell, stop

introducing heptane, but continue applying the vacuum. The remaining heptane evaporates in a few seconds because of air drawn through the cell by the vacuum pump,

4. Running a Sample Run a sample on the DIR instrument as follows: 1. Follow manufacturer’s instructions for

warm-up time, calibration and use. In general, turn on the instrument and wait the recommended time to allow the instrument to warm up. Adjust parameters such as the gain. Calibrate the instrument with the polystyrene test film each time it is turned on. Turn off the instrument at day’s end or when finished with the day’s samples.

2. Insert pen into carriage. 3. Complete the heading on the chart paper.

Align the chart paper so the pen tip is on WN 4000.

4. Fill reference and sample cells with the new oil and insert into their respective holders. Set the transmittance at 100%. Remove the sample cell, clean as described in step 3 (Cleaning the Cell Prior to Use), fill it with the used oil sample and place it in the instrument.

NOTICE To increase lab efficiency, separate the samples so that each sample within a group uses the same reference oil.

5. Run the scan, the soot can be read from the scan at WN 2000. Preparation of an overlay with the same scale as the pen carriage on the instrument will aid in determining the transmittance value at WN 2000 from the scan. The overlay can be laid on the scan and the transmittance value read directly.

For the majority of samples, a quick 3 minute scan for soot gives information of enough accuracy. Re-run samples showing questionable results using a longer scan time.

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On heavily sooted oil samples, the pen will remain at the bottom of the graph. In this case, move the instrument to WN 2000 and determine the percent transmittance. Then move the instrument back to WN 4000, and mount the external attenuator on the reference oil cell to raise the baseline. The external attenuator partially blocks the light beam to make the scan recordable. On some samples, particularly from nonengine compartments, the pen will run off the top of the chart paper. If a soot reading is required, move the instrument to WN 2000 and determine the percent transmittance. Then move the instrument back to WN 4000, and mount the external attenuator on the sample oil cell to lower the baseline. The attenuator recommended is the slotted combtype available from Perkin-Elmer, Part No. 1860390, or the equivalent from other suppliers.

Fourier Transform Infrared Analysis

The addition of FTIR analysis to the S·O·S program decreases sample test time allowing IR analysis on all samples except synthetic oils. This yields a productive savings by using the test to screen the used oil samples so the traditional physical tests (i.e., water, glycol, and fuel tests) are performed on only samples where a problem is suspected. The design of the Nicolet instrument allows much faster analysis times for oil samples. Illustration 8. The FTIR analysis has incorporated the principles discussed in the DIR section into software. The computerized instrument mathematically evaluates the differential scan, thus eliminating the graphical analysis for the technician. The following shows the relationship between the tests in the S·O·S program and the laboratory instrumentation necessary to perform those tests. The FTIR saves time and cost by screening samples so that physical tests need only be performed on suspect samples.

Test S·O·S Program S·O·S Including FTIR

Wear Metal Analysis

AA or Plasma Unit

AA or Plasma Unit

Fuel Dilution

Setaflash or GC FTIR, Setaflash 1

or GC 1 Water Hot Plate or Karl

Fischer FTIR, Hot Plate 1, Karl Fischer 1

Ethylene Glycol

Chemical Test FTIR, Chemical Test 1

Pentane Insoluables

IR (Soot Index) FTIR (Soot Index)

Toulene Insolubles

IR (Oxidation) FTIR (Oxidation)

Nitration IR (Nitration) FTIR (Nitration) Sulfur Products

IR (Sulfur) FTIR (Sulfur)

Viscosity Kinematic 2 Kinematic 2 Particle Detection

Particle Count Particle Count

1 Test performed only if positive indication from the FTIR. 2 Viscosity is also related to the IR or FTIR results for soot index,

nitration, and oxidation products in the oil.

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Glossary of FTIR Terms FTIR technique brings new equipment and procedures to the Fluid Analysis Lab. Following are definitions of some commonly used terms: Alignment - assuring the infrared laser beam follows the proper optical path whereby maximizing energy throughput. Correct the alignment only if a problem is found. Attenuated Total Reflectance (ATR) - the sample analysis technique used by the Nicolet 8210 instrument. Infrared light is directed through the crystal at a specific angle such that there are many reflections at the crystal surface prior to its exit. With a sample in contact with the crystal, a portion of the light emerges and is absorbed by the sample prior to reentering the crystal. See Illustration 9.

ATR Crystal Technique

Illustration 9.

Autoreference - a software function used to search the oil library for the closest new oil match (when new oil is unavailable or unknown). This “best match” is then automatically inserted into the system memory as if it had been selected during the reference setup. The spectra of this new oil is then subtracted from the used oil sample to achieve a difference spectrum so results can be calculated. USE OF THIS FUNCTION TO ANALYZE USED OIL IS NOT RECOMMENDED. (See Autoreference section for clarification.) Background - is a measure of the total light throughput at each specific infrared frequency and must be periodically recorded to provide a frame of reference against which a new sample is compared. This background spectrum is ratioed out of any sample measurements. The

system automatically collects a background spectrum before calibrating and before collecting a new reference. It also scans the background before collecting the first sample spectrum and after each subsequent 25 minutes of instrument use. This measurement is equivalent to that provided by the second or reference light path in a dispersive instrument. Boot - the startup sequence where the software is loaded from the hard or floppy disk into the processor memory. Calibration - done weekly, this software function corrects minor pathlength changes through the sample cell. 99% pure cyclohexane is used as a test liquid to collect data allowing the software to update operation parameters. Menu - the term describing the instrument display and the many functions which can be activated by the designated keyboard button. New oil reference - sample of the new oil used in the compartment from which the used oil sample of interest has been taken. The new oil is analyzed and the spectra stored for future use. Upon analysis the appropriate new oil reference spectra is subtracted from the used oil sample spectra and the resultant difference spectrum is then analyzed. Oil library - collection of new oil reference spectra stored on disk for fast access during instrument operation. Performance Test - peak to peak noise ratio. (Compares the instruments background signal without a sample to that with a sample.) Performed daily or every 100 samples for ATR’s. Program disk - contains the software for operation of the Nicolet 8210 instrument. This is the main operation disk. Utility disk - contains programs for miscellaneous tasks that run from the disk operating system. Programs exist to format and copy other disks.

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FTIR File Organization Most standard FTIR’s in use today have computer capabilities. The systems used in S·O·S have proprietary Caterpillar software contained on the program disk. The software programs give the Caterpillar organization a competitive advantage, as other purchasers of the instrumentation will not receive the Caterpillar proprietary software. The information from reference oil scans is stored in the new oil library on the disk. The lab will probably need several disks to store all the different reference oils, unless the system is equipped with a hard drive. Multiple copies of the program disk may be made for daily use. Keep the master disk in a safe place for back-up. Guidelines for organizing the reference oil library are as follows: 1. Since multiple disks can be used to store

the reference oil library, plan ahead and organize the reference library in an easy to use manner which will allow for growth in the number of reference oils. For example, individual disks should be set aside for different types of oil such as engine, transmission, final drive, and hydraulic.

2. When performing the calibration procedure, designate one disk containing a copy of the program to always be used in the disk drive. If the system requires a software reload or “boot”, be sure the designated disk is in the disk drive. This will ensure the current calibration is loaded in the computer memory.

FTIR Operational Guidelines The manufacturer’s instruction manual provides a good explanation of all operational details. Please read the manual. The following is intended as a general overview for operating this instrument: 1. Maintain a record book with the machine’s

calibration, alignment information and the date(s) the desiccant is changed. This maintenance history will help resolve future problems. Calibration should be done (at a

minimum) weekly. Alignment should be done only if a problem exists.

When alignment is performed, the unitless numbers flashing in the column on the left side of the display indicate the instrument’s energy throughput. When the cell is new the absolute values for the left hand column should be greater than 18,000. Energy throughput will decline as the cell is used and becomes scratched. Replace the cell when the system does not pass the performance test after alignment. 2. Use reagent grade cyclohexane (99%

pure) for the calibration. There is no substitute fluid. Fill the cell with enough solvent to avoid total evaporation before the calibration procedure is completed. Please note that cyclohexane is not the same as simple hexane.

3. Use the “Other Functions” menu listing to obtain the “Analysis Setup” and “Instrument Setup” menu listings so the proper information can be entered for items such as analysis type, reference oil library choices, and the check cell cleaning routine.

4. Enter or choose the proper reference oil from the library. USE OF THE “AUTOREFERENCE” FUNCTION TO ANALYZE USED OIL IS NOT RECOMMENDED. (See Autoreference section for clarification.)

5. Input sample identification or use the default identification function for an automatic numbering sequence.

6. Before analysis, thoroughly shake the necessary oils in a paint shaker for three minutes minimum. Allow 20 minuted for air bubbles to dissipate before applying a sample to the cell.

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7. Run the analysis, by using the “Analyze Used Oil” function on the menu. The “Check Cell Cleaning” routine should be used.

8. Load the sample, when directed by the prompt, using the Teflon spatula provided with the instrument. Be sure the cell is entirely covered, but only a thin layer is necessary. The instrument only performs an analysis on the sample layer contacting the cell’s surface.

9. The sample can be cleaned from the cell when the “Processing Data” message is seen on the display and the printout begins.

10. To clean, BLOT the excess oil off with a dry paper towel. (Some dealers use the vacuum pump connected to a nonscratch hose tip (i.e., Teflon) to remove the oil.) After blotting, flood with heptane and wipe away the remaining oil and heptane with a soft facial tissue that has not been treated with a chemical or cleaner that will leave a film on the cell’s surface. A coarse paper product, such as a paper towel, can scratch the cell and should not be used except to blot. Repeat as necessary. The cell must be clean with no remaining sample layer. This is similar to cleaning a mirror, no sample film should be visible. The instruments “Check Cell Cleaning” function will verify the cell cleanliness.

Results Analysis for samples from diesel, natural gas, and gasoline engines is available in a customized format. Caterpillar recommendations on the percent of maximum allowable limits are available only on the diesel and natural gas engines. These recommendations are intended ONLY for Caterpillar diesel or natural gas engines. For other than Caterpillar equipment we recommend trending the absorbance values. Limits for gasoline analysis must be developed by the dealership for the vehicle’s specific working applications. Value trending is recommended. The percent of maximum safe limits is the proprietary portion of the software. The results for soot, oxidation, nitration, and sulfates are adjusted to the percentage of allowable levels using the information published in Table 1 of this bulletin. These are the same conversion factors used with the DIR analysis. Instrument limitations exist when determining low levels of fuel, water, and glycol contaminants in the oil. Caterpillar software uses the following guidelines:

Fuel Percent Guideline 0% - 2% Not Detected 2% - 4% Safe, Below Limit

4% and above Possible

Water and Glycol Percent Guideline

0% - 0.05% Not Detected 0.05% and

above Possible

Other compartments, such as transmissions, final drives, and hydraulics can be evaluated with the diesel engine analysis format. The information for oxidation, water, and glycol would be of interest, and can be reported to the customer. The percent of the maximum allowable limit information provided for oxidation is valid for engines only, and trend analysis techniques should be used for all other compartments.

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Evaluation of Results Test results accuracy depends upon using the correct reference oil. If there is any question about the reference oil stored on the disk, calibrate the instrument and run a new reference oil against the reference in question. The analysis results should be between 93% and 100% transmittance and all other components should be reported as not detected. These results indicate the original reference oil on the disk is similar to the oil placed on the sample cell. If any other results are achieved, rerun the new reference oil and replace the old reference stored on disk. The results which are most sensitive to using the correct reference are fuel (volatiles), water and glycol. The instrument can be used to screen the samples and reduce physical testing. If a contaminant is rated as “possible” then the physical test must be performed to verify the results. This is primarily done to ensure the customer has not changed the oil brand or formulation in that compartment, used a different oil when topping off, or added an oil additive which may have produced falsely positive results. If a contaminate is rated as not detected, no further action is required. The instrument is programmed to err to the positive. This means the instrument may report positive fuel, water or glycol when none exists, it should seldom if ever report negative if there is contamination. It is estimated 70% to 80% of the samples do not require physical tests.

Autoreference THE “AUTOREFERENCE” FEATURE SHOULD BE USED IF, AND ONLY IF, THE NEW OIL REFERENCE IS NOT AVAILABLE! For best results, perform “Autoreference” using a disk with a large new oil reference library (40 or greater new oil references) used in the dealership’s area. The FTIR’s operating principle is to scan new and used oil and calculate the difference. The instrument then calculates the amount (% allowable) or presence of contaminants. With the “Autoreference” function the chosen reference oil is the one with a scan most similar to the used oil sample scan. The correct reference oil may have a scan quite different from the reference oil chosen by the “Autoreference” function. The “Autoreference” scan results should not be used for anything other than soot and gross oxidation. Physical tests MUST ALWAYS be performed when using “Autoreference”. This function is NOT ACCURATE in detecting the presence of fuel, water and glycol.

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©1993 Caterpillar Inc. SEBF3117-01 Printed in U.S.A. (6/93)