16
Rapid Oil Analysis

Rapid Oil Analisys

Embed Size (px)

Citation preview

Rapid Oil Analysis

TEXACO STAR TREATMENT IS JUST A CALL AWAYATLANTAB. C. EllisP.O. Box 4582Atlanta, GA 30302

(404) 321-4411

BOSTONR. G. Thiers1 University Office ParkWaltham, MA 02254

(617) 894-6010

CHICAGOJ. M. Roach2905 Butterfield RoadOak Brook, IL 60521

(312) 654-4630

DALLASR. T. ButtsP.O. Box 152045Irving, TX 75015

(214) 258-7909

(915) 772-1433

EL PASOE H. Van DykeJ. A. SpithillP.O. Box 20005El Paso, TX 79998

NEW ORLEANSW. L. Arthur4051 Veterans Memorial Blvd.Metairie, LA 70010

(504) 885-7200

NEW YORKA. H. Lowman580 White Plains RoadTarrytown, NY 10591

(914) 332-1000

ORLANDON. S. Lynch3555 Maguire Blvd.Orlando, FL 32803

(305) 894-6411

PHILADELPHIAW. M. Martin303 Fellowship RoadMoorestown, NJ 08057

(609) 778-1400

SEATTLER. P. Miller10602 N.E. 38th PlaceKirkland, WA 98033

(206) 827-0761

HOUSTON TULSAD. L. McNeil T.J. Patterson2000 North Loop West P.O. Box 2420Houston, TX 77018 Tulsa, OK 74102

(713) 686-1311

LOS ANGELES WASHINGTONA. B. Kubitski W.S. Futch3350 Wilshire Blvd. 3800 Pickett RoadLos Angeles, CA 90010 Fairfax, VA 22031

(213) 739-7100

MIDWEST LUBE DIVISIONR. A. Edmonds2905 Butterfield RoadOak Brook, IL 60521

(312) 920-9850

(918) 560-6000

(703) 425-6800

A Technical Publication Devoted to the Selection and Use of LubricantsPublished by

Texaco Inc. 2000 Westchester Avenue, White Plains, N.Y. 10650

Officers of Texaco Inc,: John K. McKinley, Chairman and Chief Executive OfficerR G Bdnkman, Vice-President and Treasurer; C. B. Davidson, Secretary.

Officers of Texaco Canada Inc.: J. L, Dunlap, President and Chief Executive Officer;K. D. Keegan, Vice-President and Treasurer; E. J, Little, Secretary.

Volume 70 Number 2 1984

To request a new subscription, obtain back issues, or to report a change of address (enclose mailing label), please write to:In the United States:

R. W. Strecker, Texaco Inc., 2000 Westchester Avenue, White Plains, N.Y. 10650In Canada:

D. E. Presley, Texaco Canada Inc., 90 Wynford Drive, Don Mills, Ontario M3C 1K5 Canada

COPYRIGHTS: The contents of LUBRICATION are copyrighted and cannot be reprinted legally by other publicationswithout written prior approval from Texaco and then only if the article is quoted exactly and accompanied by the creditline "Courtesy of Texaco’s magazine LUBRICATION". Copyright © 1984 by Texaco Inc. Copyright under InternationalCopyright Convention. All rights reserved under Pan American Copyright Convention.

EDITOR: FRANK H. PINCHBECK PUBLISHER: R. W. STRECKER

RAPID OIL ANALYSISR. W. Erickson and W. V. Taylor, Jr.

R apid analysis of used lubricating oils hasbecome a major part of maintenance pro-

. grams for many operators of automotive andindustrial equipment? The high cost of parts andlabor, coupled with the cost of downtime for equip-ment which has been idled by mechanical or lubri-cant-related failures, provides a strong incentive forconducting used oil analysis on a regular schedule.This type of regular analysis can contribute signifi-cantly to the success of a preventive maintenanceprogram.

While periodic examination of the condition oflubricating oils has been recommended by equip-ment manufacturers for many years, it is only in thepast fifteen years that analysis services have beenwidely available. Prior to that time, only the largestcorporations had the in-house facilities to conductlubricant analysis, and the services provided by lubri-cant suppliers were directed primarily toward meet-ing the needs of major lubricant customers andresponding to customer complaints. A significantexception was the service provided to owners oroperators of large ships, particularly steam turbinedriven vessels.2 Those vessels are characterized byhaving an extremely large system oil charge, an

operating environment in which water contaminationis often severe, and propulsion systems that are veryexpensive to repair or replace.

A major increase in awareness of the value oflubricant analysis as part of a preventive mainte-nance program occurred during the Vietnam conflict.That military operation saw extensive use of helicop-ters and jet-powered aircraft, both of which are sen-sitive to mechanical or lubricant-related problems.The military services determined that mobile labora-tories were required on-site, and that spectrographicanalyzers to determine wear metals and contami-nants were a vital part of such installations.

It was logical that the procedures developed forminimizing the failures of military aircraft would berecognized by industry as a means of controllingmaintenance costs and of increasing safety. Thecommercial airlines were among the first to set upelaborate laboratories for the analysis of their jetengine oils. Publicity relating the success of theseefforts in reducing engine failures, and extending thetime interval between major overhauls, soon led to ademand for commercial laboratories which couldprovide analysis service for a variety of used lubri-cants.

13

LUBRICATION

Today, rapid oil analysis services are available forthe engines of bus and truck fleets, hydraulic sys-tems of industrial plants, paper machine lubricantsystems, diesel and steam turbine powered ships,natural gas fueled engines driving pumps and com-pressors, and nearly the entire spectrum of equip-ment requiring oil lubrication. The cost of laboratoryanalysis can easily be justified when it is part of acomprehensive preventive maintenance plandirected toward eliminating or minimizing cata-strophic failures and extending the useful life ofexpensive equipment.

Rapid oil analysis is not specifically intended as ameans of determining oil drain intervals or of provid-ing a basis for selecting a particular type of lubricant.These are decisions which should be made by themaintenance supervisor or shop foreman afterreviewing the equipment manufacturer’s recommen-dations and consulting with the lubricant engineer.Analytical data will be most effectively used by themaintenance supervisor in scheduling preventiveinspections of the machinery and confirming suit-ability of the lubricant for further service between oildrain intervals. If a decision is made to extend theperiods between oil changes, regular periodic analy-ses should be conducted and a record of operatinghours, oil consumption, and filter changes should bemaintained. A history of spectrometric metal levelsand chemical analysis results is particularly impor-tant when lubricant service periods are increased.

SAMPLE COLLECTION ANDSUBMITTAL

The first step in a rapid oil analysis program is toobtain a sample which is representative of the lubri-cant in the system. The importance of this step can-not be overemphasized because the interpretation ofresults of the laboratory analyses can only be as validas the sample is representative. For example, waterand sediment observed in a sample obtained from alow point in a system and where the oil is stagnantare, in all likelihood, meaningless observations. Simi-larly, an analysis on a truly representative sample ofoil drawn into a dirty container is equally mean-ingless.

For rapid oil analysis results to be of value, sam-ples must be drawn into clean containers from aflowing system at operating temperature. Handpumps are available which can withdraw a samplefrom the lubricant sump or crankcase directly into asample bottle. The oil does not get into the pumpbody, so it is necessary to clean only the flexiblesample tube and replace the sample bottle betweensuccessive samples. Alternatively, samples can betaken during an oil drain soon after operation whilethe equipment is still at service temperature.

To avoid mixups, a sample should be labeledimmediately. A description of the equipment and typeof service, identification of the lubricant used, date ofsampling, time since last oil change, and makeup

TABLE IBASIC TEST SCHEDULE FOR USED ENGINE OILS

Enqine TypeASTM Natural Automotive Marine

Property Method Gasoline Gas Diesel Diesel

Appearance -- X X X XOdor -- X X X XWater (Crackle) -- X X X X

(Distillation) D 95 (a) (a) (a) (a)Viscosity, (~ 40C D 445 X X X XFuel Dilution

(Distillation) D 322 (b) -- -- --(Gas Chromatography) D 3524 -- -- (b) (c)

Fuel Soot -- -- -- (d) --Pentane Insolubles D 893 -- -- -- XAsh Content D 874 -- -- -- XEmission Spectrometry -- X X X XGlycol Content D 2982 (e) (e) (e) --Infrared Spectrometry ~ -- (f) -- --Neutralization No. D 664 -- -- (g) --Total Base Number D 2896 -- -- -- X(a) Determined only if crackle test is positive.(b) Determined if viscosity is low or if fuel dilution is critical.(c) Estimated from flash point.(d) Determined if viscosity is high or if fuel soot is critical.(e)Determined if boron and sodium are present in emission spectrometry.(f) For determination of oxidation and/or nitration.(g) Determined only for critical engines or if additive level is low.

14

LUBRICATION

rate, if applicable, should be recorded and submittedwith the sample. The sample should then be deliv-ered to the laboratory as rapidly as possible. Thefollowing discussion will describe procedures whichare used by the oil analysis laboratory, and the waythat the results of those procedures can be inter-preted in evaluating the condition of the equipmentand the lubricant.

TEST DESCRIPTIONS ANDSIGNIFICANCE

The laboratory analyst will select tests to be run ona used oil sample on the basis of the type and gradeof oil, the equipment it was taken from, and often asensory examination of the sample.3,’~,S,s A list ofcommon analytical methods applied to used enginelubricating oils is given in Table I. Analytical methodsfrequently applied to used industrial lubricating oilsare shown in Table II. While a detailed description ofthe test methods is beyond the scope of this article, abrief discussion of each method is included to assistin defining the significance of the test. A moredetailed description of the methods is contained inthe 1984 Annual Book of ASTM Standards, Volumes5.01, 5.02, 5.03, and 14.02.7

Sensory InspectionsAlthough appearance and odor are subjective

inspections, an experienced observer can recognizewhether the sample is typical of the product and typeof service. Evidence of contamination or deteriora-tion can often be detected by sensory examination.Diesel engine oils, for example, quickly develop ablack color due to dispersed fuel soot. Engine oils inshort service or those exhibiting little or no degrada-tion have a bland or an additive odor, similar to that ofthe unused oil. Those with longer service underfavorable operating conditions have a normal "used"

odor. The presence of significant amounts of fuel inan engine crankcase sample can be detected byodor and possibly by a thinning of consistency, whilean oil which has undergone extended service orsevere operating conditions may have a burnt odorand be noticeably thickened.

Appearance and odor are particularly significant inthe examination of compressor, turbine, and hydrau-lic oils. In normal service these oils are bright andclear, and have a bland odor. While all petroleum oilsmay contain some dissolved water, the presence ofeven a small amount of suspended "free" water willcause the oil to be hazy, and a larger amount of waterwill result in a cloudy appearance. These conditionsare shown in Figure 1. The oil to the left is dry andclear and the reference line behind the bottle issharply defined. The middle bottle, which contains200 parts per million (ppm) water, is hazy while thebottle on the right with 400 ppm water is so cloudythat the line can barely be seen. Greater quantities ofwater will coalesce and free water droplets will beseen at the bottom of the container. Water separationproperties of an oil gradually deteriorate in serviceand when contaminants are present.

A significant darkening from the normal color is anindication of contamination or oxidation, and theseconditions can often be confirmed by characteristicodors. A sharp or burnt odor is indicative of severeoxidation, and certain chemical contaminants can beindicated by odors described by terms such as fuel,chlorinated solvent, or sour gas, i.e., a gas containingsulfur compounds.* The analyst will normally call foradditional tests to confirm these indications.

*Care should be taken in checking the odor of used oilsamples as they may contain irritating material. For exam-ple, compressor oil used in a commercial refrigeration sys-tem may contain ammonia which can have a severe effecton the respiratory tract.

TABLE IIBASIC TEST SCHEDULE FOR USED INDUSTRIAL OILS

ASTM Compressor Gear Turbine HydraulicProperty Method Oil Oil Oil Oil

Appearance -- X X X XOdor -- (a) X X XWater (Crackle) -- -- X -- --

(Karl Fischer) D 1744 (b) X (b) (b)Viscosity, (~ 40 D 445 X -- X X

(/~100 D 445 -- X -- --Toluene Insolubles D 893 -- X -- --Emission Spectrometry -- X X X XInfrared Spectrometry -- X -- X XNeutralization No. D 664 (c) (c) (c) (c)Particle Count F 661 (d) -- (d) (d)(a)Use caution when examining oils from ammonia or other noxious gas systems.(b)Determined if sample is hazy or if water content is critical.(c) Determined when sensory or infrared methods indicate need.(d)Determined if cleanliness is a major criterion or to meet equipment manufacturers’ recommendations.

15

LUBRICATION

Figure 1--Various degrees of water contamination in a clear petroleum product.

Examination of the interior of the sample containermay reveal the presence of dirt granules, paint chipsor flakes of metal. Microscopic examination and/orX-ray diffraction analyses often lead to the identifica-tion of such particles.

Chemical and Physical TestsWater Content

The crackle test is the most useful screening testfor the presence of water in an oil. The test can beconducted by placing a few drops of oil in a small cupmade from aluminum foil and heating rapidly over asmall flame or on a hot plate, as shown in Figure 2. Analternative method involves the use of a hot electricsoldering iron which is immersed in the oil, as shown

Figure 2~rackle test for water using a small aluminum foil cup on ahot plate.

in Figure 3. In these methods an audible cracklingsound may be indicative of as little as 0.1 per cent freewater.

When a positive crackle test is observed, a quan-titative test for water by distillation (ASTM D 95) Karl Fischer (ASTM D 1744) should be made. Theapparatus used for determining water by ASTM D 95

Figure 3~Crackle test for water using a hot soldering iron.

16

LUBRICATION

is shown in Figure 4. In this test, a measured quantityof oil is dissolved in a water-immiscible hydrocarbonsolvent such as xylene and heated in a distillationflask. The boiling solvent drives the water vapor alongwith its own vapor upward into a condenser where thevapors condense and fall into a calibrated trap. Theheavier water settles to the bottom of the trap whereits volume can be measured, while the solvent over-flows back to the distillation flask.

dissolved water concentrations in the parts per mil-lion range, but it is normally used only for relativelyclean industrial oils or unused engine oils, sincecombustion residues in used engine oils may causefouling of the sensitive electrodes in the apparatus.

The presence of water in a lubricant system isindicative of contamination through leaking seals,blowby of combustion gases, coolant seepage, orimproper storage or application of the oil. Free wateris a prime cause of rusting, sludging, and impairedlubrication, so the source of water should be locatedand eliminated as soon as possible.

Figure 4---The apparatus for determining water in petroleum prod-ucts, ASTM D 95.

In the Karl Fischer method, the water present in asmall weighed sample of oil is titrated with a complexsolution of iodine and sulfur dioxide in pyridine, andthe water concentration is calculated from the volumeof iodine solution consumed and a factor for themilligrams of water equivalent to a millilitre of theiodine solution*. Many laboratories are nowequipped with an automated apparatus in which theiodine solution is generated coulometrically and thewater concentration is calculated and displayed byan electronic readout device. One such instrument isshown in Figure 5. The Karl Fischer method has theadvantage of being able to determine both free and

*The solution is called a titrant and chemical procedures ofthis type are commonly referred to as titrations.

Figure 5--An automated apparatus for determining water inpetroleum products using the Karl Fischer method.

ViscosityViscosity is the most important single physical

property of a lubricating oil. It is a measure ofresistance to flow resulting from internal friction of themolecules moving past each other under stress. It isthe sole property of a lubricant that influences the oilfilm thickness between moving parts and hence influ-ences wear. An oil of inadequate viscosity will notform films sufficiently thick to prevent or minimizewear, whereas an oil of unduly high viscosity willgenerate unnecessary heat and waste energy. Theease of starting an automotive engine on a frigidwinter morning depends largely on the viscosity ofthe crankcase oil. Viscosity is also an essential con-sideration in the proper functioning of hydraulic sys-tems, automatic transmissions, and shock absorb-ers.8

Temperature is the factor which has the greatesteffect on viscosity, and laboratory determinationsmust be made under precisely controlled tem-perature conditions. While several methods for deter-mination of viscosity are available, the kinematicmethod (ASTM D 445) is the one most commonlyused for lubricating oils? In the kinematic method, ameasured volume of oil is passed through a capillarytube and the time of passage is precisely deter-mined. The viscosity, designated in centistokes (cSt),is calculated from the time and a calibration factor for

17

LUBRICATION

Figure 6~A constant-temperature bath containing several glasscapillary kinematic viscometers, ASTM D 445.

the capillary used. Figure 6 illustrates an apparatusfor the determination of viscosity.

The analyst compares the viscosity determined forthe used oil sample against the standard value for anunused oil of that grade. A deviation of less than10 per cent from the mid-point of the ISO viscosityrange of the unused oil is usually considered normal.Greater deviations from the standard value may indi-cate use of the wrong grade or a mixture of oils,thickening due to oxidation or fuel soot contamina-tion, or thinning due to fuel dilution. In the case of fueldilution, the quantity of No. 2 diesel fuel in a crank-case oil sample can be estimated from the reductionin viscosity as shown in Figure 7. This value can be

confirmed by a gas chromatographic determina-tion.1°

Fuel dilution in gasoline engine oils is determinedby steam distillation (ASTM Method D 322). In thistest measured volumes of used crankcase oil andwater are placed in a flask and distilled. The distillate(gasoline and water) is collected in a graduatedreceiver as illustrated in Figure 8. The gasoline floatson the water in the receiver, its volume is measured,and the percentage gasoline in the oil is calculated.

The presence of 5 per cent fuel diluent can result ina viscosity reduction equal to approximately oneSAE grade. This is normally taken as an indication ofsignificant fuel system problems and the need for anoil drain. When an oil is diluted excessively, an ade-quate hydrodynamic lubricating film is not main-tained between the moving parts and metal-to-metalcontact follows, resulting in increased wear and pos-sible bearing failure. The presence of fuel soot oroxidative degradation of the oil can result in anincrease in viscosity, which in turn can mask thepresence of fuel diluent. When fuel soot is greaterthan 4 per cent with no increase in viscosity, fueldilution should be determined.

Deviations in the viscosity of in-service industriallubricants are often the result of using the wrongviscosity grade of oil as makeup to the system. Othercauses of viscosity changes are leakage from anadjacent compartment or dilution by a process fluidsuch as is sometimes encountered in compressorservice when oil soluble gases are being com-pressed.

I I I I I4 6 8 I0 12

DIESEL FUEL DILUTION,

Figure 7--Viscosity-dilution curves for four grades of crankcase lubricants.

18

LUBRICATION

the soot content. Reference spots made by oil withknown soot content assist in estimating the soot con-tent of the used oil sample.

For dark or cloudy high viscosity oils, such as gearoils, a determination of particulate contaminants, aswell as water content, can be made by centrifugationin a cone-shaped tube (ASTM D 893). A measuredportion (25 or 50 millilitres) of the oil is placed in thetube, and an appropriate solvent (pentane ortoluene) is added up to the 100 ml mark. After thor-oughly mixing the oil and solvent, the tube is placedin a centrifuge. Regardless of the solvent used, waterand sediment become concentrated in the bottom ofthe centrifuge tube and can be measured by refer-ence to the graduated marks on the tube.

In this method, if pentane is used as the solvent,wear metal particles and foreign contaminants suchas dirt and water are collected in the tip of the tubeafter centrifuging. Oil oxidation products tend to con-centrate at the interface between the water and oilphases. If toluene is used as the solvent, the cen-trifuge method will show the wear metals and foreigncontaminants along with the water, while the oiloxidation products will normally be dissolved. If par-ticulate sediment is present it can be recovered fromthe tube for further characterization.

Figure 8---The apparatus for determining gasoline dilution in crank-case oils, ASTM D 322.

Insolubles or SedimentThere are several methods for measuring insolu-

bles in an oil. These include filtration, centrifugation,blotter spot tests, and optical methods. The mostcommon insoluble contaminant in diesel engine oilsis fuel soot, since diesel fuel combustion is by naturemore sooty than gasoline or natural gas combustion.The formation of soot is more severe under certainabnormal operating conditions, such as overfuelingor a restricted air intake.

A simple method for the estimation of fuel sootcontent in a diesel engine oil is the optical procedurein which a very small, measured amount of used oil isplaced in a clear tall-form glass inspection bottle filledwith toluene, shaken, and visually compared withstandards prepared using oils with known fuel sootcontent. This method compares favorably with theblotter spot method. In the latter method, severaldrops of oil are placed on a piece of blotter paper andallowed to sit for several hours until the oil diffusion iscomplete. As the oil spot diffuses from the point ofapplication, the insoluble fuel soot remains at thecenter as a dark spot with an intensity proportional to

Emission Spectrographic AnalysisThe identification of inorganic contaminants, as

well as the metallo-organic oil additive elements, isaccomplished by use of the emission spectrometer.The sample excitation stand of an emission spec-trometer for oil analysis is shown in Figure 9. In thisinstrument a film of oil is carried on a rotating graphitewheel to a sharpened graphite rod electrode where itis subjected to a high voltage arc. The metallic ele-ments in the sample are excited by the energy of thearc and each emits a characteristic spectrum of lightwhich is collected and measured by a series of pho-tomultiplier tubes. The light intensities are convertedto element concentrations by a computer and printedfor examination by the analyst.

Emission spectrographic analysis is a powerfultool for detecting wear metal levels. The significanceof wear metal values varies with the make and modelof the equipment and with the type of service, includ-ing working environment, drain interval, filter changeinterval, etc. Metal concentrations are normally lowand increase slowly with longer operating periods. Asudden upward change in the concentration of anymetallic element, such as copper, lead, or iron, whichis present in the lubricant-wetted parts of the equip-ment suggests an increased wear rate, and possiblyabnormal operating conditions.

The presence of silicon combined with a higherlevel of wear metals signifies the entry of dirt into thesystem. Combinations of certain trace elementsoffen provide clues to the components undergoingwear. By reference to literature supplied by the equip-

19

LUBRICATION

Figure 9---An emission spectrometer. The oil sample excitation stared is shown in the inset.

ment manufacturers and his own experience, theanalyst can often detect evidence of incipient failureand alert the customer before a severe mechanicalproblem occurs. Trends in concentrations of metalsobserved for several successive samples from thesame equipment are particularly useful in diagnosingpossible adverse conditions or operating problems.

While several modern crankcase lubricant formu-lations use boron-containing additives, the presenceof boron, usually along with sodium, in the spec-trographic analysis may also suggest the presenceof antifreeze, indicative of a glycol coolant leak. Achemical test for ethylene glycol will usually be run toconfirm the presence of the antifreeze. Glycol cancause thickening and sludge formation, and mayattack certain alloy bearings when present in a crank-case oil at levels over 0.1 per cent. When glycol ispresent at that level, the oil should be drained and thesource of coolant entry should be found and cor-rected.

Infrared AnalysisInfrared (IR) spectrometry is another powerful

technique for oil analysis which can detect organiccontaminants, water, and oil degradation products atlow levels. IR provides a simple, rapid method for

establishing (1) general lubricant type (paraffinic naphthenic) (2) the presence and often the quantityof certain contaminants, such as alcohols, polar sol-vents, and free water (but not normally dissolvedmoisture), (3) the depletion or degradation of additivecomponents, such as antioxidants, and (4) the pres-ence of lubricant degradation products resulting fromoxidation or nitration.

In normal practice a double-beam IR spectrometeris employed in the differential mode. The used oil isplaced in a cell in the sample side of the instrumentand an unused reference oil is placed in the referencecell. The instrument traces a curve which representsthe difference between the sample and the refer-ence, and clearly defines those spectral regionscharacteristic of the organic contaminant or the oildegradation products. A newer procedure for differ-ential infrared (DIR) spectrometry utilizes a FourierTransform infrared (FT/IR) analyzer in which thesample is placed in a single-beam cell and the spec-trcm is compared to that of a reference oil spectrum,which has been stored in a computer. A photographof the F-F/IR screen display (in absorbance mode)during DIR analysis of a used gas engine oil is shownin Figure 10. Use of the computer assisted FT/IRoffers convenience as well as greater sensitivity

20

LUBRICATION

Figure IO--A differential infrared spectrometer screen display showing absorbance versus wavenumber for a used gas engine oil. Thespectrometer is shown immediately above.

A particularly important application of DIR analysisis in the testing of oils from natural gas fueledengines." In these engines the combustion processfrequently promotes the fixation of nitrogen by com-bining nitrogen and oxygen from the combustion air.Nitrogen fixation is most severe in naturally aspiratedfour-cycle gas engines and with air/fuel ratios char-acterized by 0.5 to 5.5 per cent excess oxygen asmeasured in the exhaust air. The reaction of thesefixed nitrogen compounds with lubricating oil formsacidic materials which ultimately become oil insolu-ble, accelerating the formation of varnish and sludge,and promoting further oxidation and thickening of theoil.

DIR analysis is used to quantify the nitration prod-ucts, provide a basis for recommending correction of

adverse engine operating conditions, and suggestan oil change before deposit formation becomes aproblem. Knowing the characteristic DIR patterns ofused oils from various engines and by maintaining arecord of changes in absorbance ratios, it is oftenpossible to detect one or more of the following sevenconditions:

1. Hot spots on pistons or cylinder walls.2. High crankcase oil temperatures (possible faulty

cooling).3. Improper air/fuel ratio.4. Improper spark timing.5. High rates of combustion blow-by.6. Faulty operation of crankcase ventilating sys-

tem.7. Engine overload.

21

LUBRICATION

I00

9o

oc 80

704400

WATER AND/OR GLYCOL

ACID CARBONYL (OXIDATION)

NITRO COMPOUNDS(NITRATION)

NITRATE ESTER(NITRATION)

I I I I

3200 2000 1400 800WAVENUMBERS, CM-I

Figure 11--A typical differential infrared curve in the transmittance mode.

A typical DIR curve, in the more familiar transmit-tance mode, showing evidence of nitration, oxida-tion, and water and/or glycol contamination is shownin Figure 11.

Neutralization NumberWith the exception of heavy duty engine oils, which

characteristically display a fairly high degree ofalkalinity imparted by their additive components,most lubricating oils are essentially neutral. That is tosay, they do not contain acidic or alkaline compoundsand are analogous to an aqueous solution having apH of 7. Strictly speaking, a lubricating oil can nothave apH since the term is defined by reference tothe hydrogen ion concentration of a water solution.However, pH is used for convenience to indicate theacidity or alkalinity of an oil in a non-aqueous solventwhen being tested for neutralization number. Valuesof pH higher than 7 signify alkalinity, while valuesbelow 7 reflect acidity. Acidity can result fromoxidative degradation of an oil due to overextended

service intervals or abnormal operation. ApH lessthan 4 denotes the presence of strong, and probablycorrosive, acids.

Neutralization number is defined as the milligramsof potassium hydroxide required to neutralize theacidity in one gram of oil. The alkalinity of an oil isdefined as the quantity of hydrochloric acid,expressed in terms of the equivalent number of mili-grams of potassium hydroxide, to neutralize onegram of oil. Titration (reaction of the dissolved oilsample with a standardized solution of either acid orbase) is used to determine the neutralization numberof an oil. Results can be expressed in terms of totalbase number (TBN), total acid number (TAN), strong acid number (SAN). Methods in common usefor determining the neutralization numbers of oilsinclude: ASTM D 664, an electrometric titration usinga recording potentiometer for determination of TBN,TAN, SAN, and initial pH; ASTM D 974, a colorimetrictitration for determining TAN; and ASTM D 2896, anelectrometric titration for TBN using perchloric acid inglacial acetic acid as titrant.

22

LUBRICATION

Figure 12--Particle count determinations are made in this automated apparatus.

TBN is a measure of the alkaline or basic compo-nents of an engine oil. Alkalinity is imparted to the oilby the additive components, and the level of alkalinityof an unused oil is characteristic of the type of servicefor which the oil is designed. Engine oils for moderateservice such as automotive or light truck operationhave relatively low levels of alkalinity. The alkalinitylevels of oils for engines in heavy construction equip-ment are in an intermediate range. Oils designed forextended operation under severe conditions, such aslarge slow-speed diesel engines operating with ahigh sulfur content fuel oil, have a high alkalinity. Inorder to avoid corrosion of oil-wetted parts of thesystem, engine oils must be replaced when their TBNfalls below a prescribed level.

Particle CountModern high capacity turbine systems, the sophis-

ticated hydraulic systems of automated machinetools, and newer paper machine circulating systems

have placed a new demand on the oil analysis labo-ratory. The detection and quantitative measurementof particulate matter in the lubricant is of great con-cern, since several major equipment manufacturersrecommend fine filtration of the oil. Regular periodicdetermination of particle count is recommended bythese manufacturers as part of a used oil analysisprogram.

There are several instruments available for makingparticle counts on lubricating oils. The measurementprinciple is either a photometric or an electricalresistivity measurement while the oil is passedthrough a small orifice. In one widely used instru-ment, shown in Figure 12, a fixed volume of the oilsample is pumped by air pressure through the mea-suring orifice at a fixed flow rate while a collimatedbeam of light is passed across the orifice at rightangles. The beam of light is attenuated by the parti-cles before reaching the photodiode detector and thereduction in light intensity is proportional to the area

23

LUBRICATION

of the particle divided by the area of the detectorwindow. The results are read from a series of sixelectronic counters which have accumulated theresults during the counting period. These results arethen normalized and expressed as the number ofparticles in each of five size ranges per 100 millilitresof sample.

The significance of a particle count determinationis established when the values for a used oil arecompared with criteria defined by the equipmentmanufacturer. Particle size ranges in microns(micrometres) that are often used in defining lubricat-ing oil cleanliness are: 5 to 10, 10 to 25, 25 to 50, 50 to100, and over 100.

SUMMARYRapid analysis of used lubricating oil can be a

significant factor in establishing a preventive mainte-

nance program for automotive and industrial equip-ment. Samples are taken from the operating equip-ment according to an established schedule based onhours of operation or miles of service, or by calendarperiod for continuously operating units. The samplesshould be forwarded to the laboratory promptly, andtesting should be completed in a timely manner. Lab-oratory specialists select appropriate tests fromthose outlined above on the basis of the type andmodel of the equipment and the service conditions.The shop foreman or maintenance supervisor shouldbe alerted promptly in the event that analysis revealsa condition which could lead to equipment failure orrequire prompt corrective action. While it can notreveal every bearing, gear or system componentproblem, rapid used oil analysis, with intelligent,experienced interpretation of the test results, canmake a significant contribution to a well-planned pre-ventive maintenance program.

REFERENCES

1. Steenbergen, J.E., "Comprehensive Lube Oil AnalysisPrograms: A Cost-Effective Preventive MaintenanceTool," LUBRICATION ENGINEERING, 34, pp 625-628,1978.

2. Cashin, R.E, "Marine Turbine and Diesel Engine OilAnalysis," LUBRICATION, Vol. 56, No. 3, 1970.

3. Snook, W.A., "Used Engine Oil Analysis," LUBRICA-TION, Vol. 54, No. 9, 1968.

4. Tarbell, L.E., "Analysis of Used Refrigeration Com-pressor Lubricants," LUBRICATION, VoI. 57, No. 1,1971.

5. Vail, O.D., "Used Compressor Oil Analysis," LUBRICA-TION, Vol. 63, No. 3, 1977.

6. Young, C.H., "Used Hydraulic Oil Anlaysis," LUBRICA-TION, Vol. 63, No. 4, 1977.

7. American Society for Testing and Materials, Phila-delphia, PA, 1984.

8. Rein, S.W., "Viscosity-I," LUBRICATION, Vol. 64, No. 1,1978.

9. Rein, S.W., "Viscosity--II," LUBRICATION, Vol. 64, No.2, 1978.

10. Bauccio, M.L., "Efficient Analysis of Used LubricatingOil Using Gas Chromatography," LUBRICATIONENGINEERING, 38, pp 549-556, 1982.

11. "Gas Engines," LUBRICATION, VoI. 53, No .1, 1967.

24

TEXCHEKRAPID OIL ANALYSIS