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1Adam Adgar School of Computing and Technology Oil AnalysisAdam AdgarSchool of Computing and Technology
2Oil Function Very important for any rotating equipment Performs two well-known, primary functions:Lubricates surfaces - reduces frictionSeparates surfaces - oil film prevents metal-metal contactTypical oil film thickness is 10 microns micronsAt actual load/contact point may be less than 1 micronOil also performs several other, related functions:Protects surfaces from corrosionCan remove contaminants and particulates in circulating systemsAssists with temperature control by absorbing / transferring heatTransmits power in hydraulic applications
3Oil Types Oil comes in two basic forms: Natural (or Mineral)Petroleum basedFrom oil deposits in the groundMore commonly used typeSyntheticMan-made lubricantBased on manufactured polymersThere are many sub-categories of each formGreaseSuspension of lubricant (both natural and synthetic) in a chemical solution.Lubricant is temperature released (temperature rises, lubricant gets released until the temperature drops again and so on)
4Why Analyze Oil Condition? Oil analysis is the leading indicator of any problems developing on a large number of different mechanical systemsOil analysis will arguably catch more potential problems across the broad range of mechanical systems than any other predictive technology (including vibration analysis).That is not to say that other technologies are not necessary or that oil analysis does not have its weaknesses (rolling element bearings being one notable example). It simply illustrates the value of a well-run oil analysis program.
5Where is Oil Analysis used? Oil analysis works particularly well on:Oil lubricated rolling element bearings Oil lubricated sleeve bearingsGearboxesEnginesTurbinesHydraulic SystemsCompressorsChillersAny system that uses lubrication and lends itself to drawing and testing samples of that lubrication.
6What does Oil Analysis Reveal ? Oil analysis can be broken into three main areas of testing Chemical composition of the oil (including the additives).Presence of contaminants (e.g. water).Particle analysis (wear particles in the oil - primarily metals - a.k.a. ferrography).It is obvious that tests should be performed on oil systems on machines that are operational. But what about incoming and stored oil - are you getting what you should be getting (what you ordered) ?Has the oil been stored properly ?Has moisture or other contaminants gotten in ? Is recycled or reclaimed oil up to the standards it should be ?
7Commonly Measured Parameters ViscosityAn oil characteristic related to it's resistance to flow.MoistureA contaminant that causes rust, corrosion and oxidation.Acid NumberA measure of acidity related both to additive presence and oxidation likelihood.Base NumberA measure of alkalinity related both to additive presence and oxidation likelihood.Particle CountRelated to component wear, contaminant ingression, corrosion and others.Presence of Various AdditivesDepletion of these can lead to serious problems.Dielectric PropertiesRelated to the likelihood of impending oxidation.There are numerous other tests that can be performed and specific tests within these general categories.Monitoring the chemical properties of the oil is one of the critical components in any oil analysis program.critical to the performance of the oil's duties.Additives help slow the degradation of the oilHaving correct oil with the appropriate chemical properties is of paramount importance.
8Oxidation Caused by heat, air bubbles, water and metal particles Chemical process that changes oil molecular structureVery common problem monitored by oil sampling and testingResults in an increase in oxides, acids, polymers and sludgeOil properties change in that the viscosity increases (it gets thicker), it darkens and changes its odor.Can be monitored by (amongst others)Viscosity MeasurementFourier Transform Infrared Spectroscopy (FTIR)
9Viscosity Testing Kinematic Viscosity Capillary viscometer Measures oil's resistance to flow due to gravity.Units are "centistokes" (cSt)Capillary viscometerThis U-shaped tube is filled with oil.Suction is applied that lifts the oil up one side of the tube to a "start" line.The tube is then submerged in a temperature controlled water bath (40C or 100C)Oil allowed to flow from the start line to the stop line under gravity.The time it takes represents the viscosity valueAbsolute ViscosityMeasure's an oil's resistance to flow due to internal friction.Units are "centipoise" (cPs)Brookfield (rotary) viscometerGlass tube in a temperature controlled block is filled with oilRotating spindle is submerged in the oilThe amount of torque necessary to turn the spindle at a particular rate determines the viscosity valueViscosity is a measure of an oil's resistance to flowAbsolute viscosity is considered the more reliable of the two, especially as a trending tool, because kinematic viscosity is somewhat dependent on specific gravity (which is affected by many different common contaminants).
10Effects of Incorrect Viscosity Too high (thick oil)Excessive resistance to flow causes:Additional heat to be generated - one of main causes of oxidation and sludgeOil may not flow to or through areas that it is supposed to flow (e.g. bearings, return or drain lines). Problem compounded when oil (system) is coldCavitationIncreased energy consumptionToo low (thin oil)Insufficient resistance to flow causes:Loss of proper oil film thickness - leads,to increased friction, heat buildup and effects such as oxidationSystem is more susceptible to loss of oil film in high load and slow speed areasSystem susceptible to problems generated by smaller particles than would be the case with a normal (thicker) oil filmIncreased likelihood of thermal breakdown of the oil
11Chemical Makeup: FTIR Fourier Transform Infrared Spectroscopy Common method to assess the oxidation level (or potential) in oilEspecially useful because it allows the analysis of the additives and the presence of a variety of contaminants.Some of the molecules that can be tested with this method include water, oxidation by-products, nitration, sulphation, glycol, anti-oxidants, anti-wear, soot and many more.Method:Infrared light passed through a fixed film of oil (~100 um thick)Absorbance of IR is examined at range of wavelengthsCompared to the same test on "base", or new oil. Many of the molecules being tested for (additive, contaminant molecules plus the oil molecules) absorb the IR light only at very specific wavelengths. By comparing the used oil to the new oil, an accurate assessment of the quantity and presence of these molecules can be made.
13Chemical Contaminants Some generated by processes taking place in the oil (e.g. oxidation)Others are result of outside chemical contaminants getting into the oil and include:WaterGlycolFuelAir
14Chemical Contaminants: Water Water is possibly the single most destructive contaminant that commonly gets into oil. It can get into the oil in any number of ways:Oil drum stored improperly, water standing on top slowly leaks in.Reservoir that gets water condensation on the lid, eventually drips back into the oil.Leaking or no sealsOften people make the mistake of thinking that since oil and water separate (oil on top, water on the bottom), you can see water contamination.Free Water - This is the state in which water and oil are separate.Emulsified Water - Very small droplets are dispersed (suspended) throughout the oil. In this state, the oil has a cloudy appearance.Dissolved Water - The water molecules are actually separated and thoroughly mixed with the oil molecules. Whereas emulsification has water droplets (many water molecules), dissolved water is on the molecular level. In this state, you cannot visibly detect the water
15Effects of Water Contamination Causes oxidation -significantly worse when water is present. The chemical process causes acid formation, sludge and varnish are formed and the oil is thickened.Viscosity changes - Contrary to what many suspect, water will cause the viscosity to increase (oil thickens) especially when oil emulsions are created.Dielectric changes - Water, since it conducts electricity, reduces the insulating properties of oil.Aeration - Water can accelerate aeration problems such as the formation of tiny air bubbles and the generation of foam.Attacks additives - Water chemically reacts with additives to cause effects such as sludge, acids, sediment and many more.Reduces oil film strength - Water will cause film failure and other side effects.Bacteria - Bacteria can actually can form in the water.Water also affects machine components:Corrosion - Water causes components to rust (one of the solid contaminants mentioned previously).Acids - The acids formed will also cause corrosion. Embrittlement - Loss of oil film strength and instantaneous water vaporization can cause hydrogen embrittlement of the metallic components.
16Testing for Water Contamination Testing for water in oil can be done through a variety of methods with the most common and simple being the "crackle" test.A crackle test is a test where a couple of drops of oil is put on a hot plate and heated to about 300 F (150 °C).If water is present, audible crackling will be heard as the water heats up, bubbles form and grow and finally pop.Another method is the FTIR (discussed earlier) where the presence of water will be indicated in a particular wavelength.In order to quantify the water in the oil, the Karl Fischer test is often used. This test will provide a ppm or percentage water value. Measures all water - free, emulsified and dissolved.
17Solid ContaminantsSolid (particle) contaminants can be quite destructiveDestructiveness:QuantitySizeHardnessSharpness of edgesWeightExamples include:Wear metals (depends on system components)Soot (combustion by-product)RustDirt / DustFibersSilt (class of very small particles (~ 1 micron) and can be composed of many different materialsHow destructive a particle is depends on several factors.Intuitively, you would surmise that the larger a particle is, the more destructive it is. But what if it is large but relatively soft ? So hardness is also a factor.What about how sharp the edges are ? A particle with sharp edges would be able to cause more damage than one with smooth edges.The quantity of particles is obviously a factor.Finally, the weight of a particle will affect how long it remains suspended in the oil (once it settles to the bottom of a tank, it is not destructive to machine components).
18Introduction To Ferrography Also known as Wear Debris AnalysisA powerful tool in analyzing the health of machinery.Wear particles suspended in the oil are separated by magnetic or filtration methodsExamine this debris under optical microscope (100x is standard)Analyst can gain much information on the health of the machinery from which the sample was takenRelatively simple techniqueperiodically quantify amount of wear taking place over timeidentify location and mechanism of such wearferrography (analysis of oil samples using an optical microscope). It can be very useful since it is one of the primary methods for economically pre-screening oil samples in order to significantly reduce the number of those samples being sent out to labs for more costly full testing.
20Wear Debris Particle Recognition Appearance of wear debris is related to conditions under which they were formedThis facilitates the identification of wear mechanisms.Only a limited number of ways in which surface wear can occur.Each mechanism generates particles of a specific appearance.Damage due to wear can occur by any of the following specific wear mechanisms:AbrasionGougingAdhesionCavitationErosionMicro fatigueFrettingCorrosion
21Particle Characteristics Most important parameters of the wear debris are:Extent of wearQuantityTexture / HardnessColorHow wear is occurringSizeShapeCompositionThe shape of wear particles can be classified into any of the following categories:Platelets (P)Ribbons (R)Chunks (C)Spheres (S)Heat Related Fused Particles (T)Abrasive Debris (A)Fretting Wear (F)Needles (N)Corrosion (oxidant product) (O)In analyzing the state of a mechanical system through analysis of its lubrication system properties, the most important parameters of the wear debris are:
22Particle Characteristics ColorSeverity of the wear (and hence temperature involved) is indicated by particle color.Colors range from light straw → brown → purple → blue as the temperature progressively rises (from 230 °C to 300 °C).Brass or bronze (copper based alloys) show a deep red or green discoloration from tempering.Dark discoloration on the particle surface may indicate surface oxidation (corrosion).SizeFour descriptions for categories of size classification may be used:Fine: <10 micronsSmall: micronsMedium: micronsLarge: >60 micronsWhen elevated temperatures are present during the generation of the particle, the temper colors of the wear particles are displayed due to the release of frictional energy
24ReferencesSchalcosky, D.C. and Byington, C.S. "Advances in Real Time Oil Analysis". Practicing Oil Analysis Magazine. November 2000.Barnes, M. "Fourier Transform Infrared Spectroscopy". Practicing Oil Analysis Magazine. March 2002