Application Notes on Lubricating Oil Analyses

8/19/2019 Application Notes on Lubricating Oil Analyses

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Application Notes on Lubricating Oil Analyses

In service oil analysis, also known as condition monitoring through oil analysis, has gained

wide acceptance as a predictive maintenance and cost-cutting strategy in modern industry.

In order to be effective, an in-house oil analysis program must monitor the condition of the

mechanical integrity of the machine from which the oil sample is taken. Concurrently, it

must also monitor the condition of the lubricant.

A modern condition monitoring program based on oil analysis takes the following form :

1.

Fourier-Transform Infra-Red Spectroscopy (FT-IR) is routinely used to assess thedegradation and/or contamination of Lubricating Oils. This test enables both

petroleum-based and synthetic oils to be detected for:

a) Contaminants in lubricants

b) Cross-contamination of lubricants

c) Degradation of Lubricants

Organic compounds present in lubricating oils will absorb infrared light at specific

frequencies. The most common frequencies measured in oil analysis indicate fuelsoot, oxidation, nitration, water and glycol. Reference samples, usually new oil, are

required for effective determination and interpretation.

2. Total Acid Number (TAN) is a key analytical test to determine the degree of

deterioration of in-service lubricants. The higher the acidic value of the lubricant, the

higher the degree of degradation of the lubricant. The TAN of a lubricant is

expressed as milligrams of Potassium hydroxide per gram of oil (mgKOH/g).

Analysis of lubricant for TAN is performed electrometrically using an Autotitrator.

3. Kinematic Viscosity is basically a measurement of a fluid’s resistance to flow.

Kinematic Viscosity is usually expressed as Centistokes ( cSt). Testing is typically

performed at two temperatures: 40o

Celcius and 100o Celcius. These temperatures

embrace the bulk of operating temperatures of machinery. The measurement is

performed using a Brookfield Digital Rotary Viscometer with a full range of spindles,

which are selected on the basis of Viscosity range. The method is commonly referred

to as the Brookfield method and is detailed in Standard ASTM D2983.

Monitoring and trending of Viscosity is one of the most important components of

any oil analysis program. Small changes in viscosity can be magnified at operating



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temperatures to the extent that a lubricant is no longer able to provide sufficient or

adequate lubrication.

Reduction of Viscosity can lead to:

a) Loss of oil film resulting in excessive wear.

b) Increased mechanical friction causing excessive energy consumption.

c) Increased sensitivity to particle contamination due to reduced oil film.

d) Oil film failure at high temperature, high loads or during start-ups or coast-

downs.

Increase of Viscosity can lead to:

a) Excessive heat generation resulting in oil oxidation, sludge and varnish build-up.

b) Gaseous cavitation due to inadequate oil flow to pumps and bearings.

c) Lubrication starvation due to inadequate oil flow.

d) Oil whip in journal bearings.

e) Excess energy consumption to overcome fluid friction.

f) Poor air detrainment or demulsibility.

g)

Poor cold-start pump ability.

4. Viscosity Index is a test which may prove useful in lubricant analysis. Viscosity Index

(VI) is the difference in viscosity at two different temperatures. It is commonly

known that Viscosity decreases with increasing temperature but it is not generally

known that the amount of change in viscosity is not linear.

5. Fuel Dilution is the measure of a fuel present in a lubricant. Excess fuel in oil reduces

the oil film strength due to decrease of viscosity, thereby increasing metal-to-metal

contact and wear. Excessive fuel will also cause premature oil oxidation. High Fuel

Dilution is generally caused by excessive idling, improper adjustment, and/or faulty

components within the fuel delivery system.

6. Fuel Soot (% mass) may be accurately measured by Light Extinction Measurement

(LEM) technique. Fuel soot levels are indicative of air/fuel ratios, fuel delivery and

valve settings and combustion/exhaust efficiency. The state of the fuel soot depicts

dispersant additive effectiveness.



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7. Spectrometric Oil Analysis is the measure of trace levels of wear metals present in a

lubricant. These metals may originate from moving parts wear, as well as from

external contamination. Metals may also be present due to additive treat of oil.

Table 1 showing metals typically present in a lubricating system.

Wear Metals External Contaminants Additives

Aluminium as Al Boron as B Barium as Ba

Cadmium as Cd Calcium as Ca Boron as B

Chromium as Cr Potassium as K Calcium as Ca

Copper as Cu Silicon as Si Chromium as Cr

Iron as Fe Sodium as Na Copper as Cu

Lead as Pb Magnesium as Mg

Magnesium as Mg Molybdenum as Mo

Manganese as Mn Phosphorus as P

Nickel as Ni Silicon as Si

Silver as Ag Zinc as Zn

Tin as Sn

Titanium as Ti

Vanadium as V

Zinc as Zn

8. Particle Shape is determined using high-power Trinocular Microscopy which captures

the silhouette image of particles in oil. The image of the particles in the sample is

captured by a USB camera and stored in computer memory using a specific software

package. The objects are then analysed for size and shape characteristics which are then

used to classify particles into wear classes. Air bubbles are recognised and eliminated

from the count and water droplets are recognised, classified and quantified.

If we examine an ISO code of a LUBRICANT of, say 16/14/11, this basically means that :

a. 16 is the number of particles greater than 4 microns in diameter.

b. 14 is referring to the number of particles equal to or greater than 6 microns.

c. 11 is referring to the number of particles equal to or greater than 14 microns.

These particle diameters are derived from the ISO Standard 11171 and are used in all

modern analytical laboratories. Particle sizing is measured using a Malvern Particle

Sizing Laser Counting Analyser.



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Wear Metals and Additives

Iron Indicates wear originating from rings, shafts, gears, valve train,

Cylinder walls and pistons in some engines

Chromium Primary sources are chromed parts such as rings, liners etc.

and some coolant additives

Nickel Secondary indicator of wear from bearings, shafts and valves

Aluminium Indicates piston wear, rod bearings and bushings

Lead In diesel engines, overlay of most ma/rod bearings.

In Petrol engines, mostly from Tetraethyl Lead contamination.

Copper Wear from bearings, rocker arm bushings, wrist-pin bushings,

thrust washers, bronze and brass parts. In some transmission,

wear from discs and clutch plates. Oil additive or anti-seize

compound.

Tin Indicates wear from bearings when babbit overlays are used.

Tin is also an indicator of piston wear in some engines.

Silver Bearings wear, secondary indicator of oil cooler problems,

especially if coolant sample is detected.

Titanium Alloy in high quality steel for gears and bearings.



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Wear Metals and Additives

Silicon Airborne dust and dirt contamination.

Boron Coolant additive, used as an additive in some oils.

Sodium Coolant additive, used as an additive in some oils.

Potassium Coolant additive

Zinc Antioxidants, corrosion inhibitors, anti-wear additives,

detergents, extreme pressure additives.

Molybdenum Indicates ring wear. Used as an additive in some oils.

Phosphorus Antirust agents, spark-plug and combustion chamber deposits

Calcium. Detergents, Dispersants, acid neutralizers.

Barium Corrosion inhibitors, Detergents, Rust Inhibitors

Magnesium Dispersant, Detergent additive, alloying metal.

Antimony Bearing overlay alloy or oil additive.

Vanadium Heavy fuel contaminant



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Lubricating Oil Testing Laboratory

All methods listed are American Society for Testing and Materials (ASTM)

Method Reference Test

D-2007 Aromatics by isolation

D-2007 Asphaltenes

D-445 Kinematic Viscosity cSt

D-664 Total Acid Number TAN

D-287 API Gravity

D-482 Ash Content

D-2896 Total Base Number TBN

D-808 Chlorine in new and used oils

D-2500 Cloud Point

D-189 Carbon Residues

D-130 Copper Strip corrosion

D-322 Fuel Dilution % volume

D-86 Distillation of Petroleum products

D-93 Flash Point Determination

D-2982 Glycols estimation

D-3228 Total Nitrogen Content

D-4047 Additive Content of Lubricating Oils

D-97 Pour Point

D-473 Sediment Content

D-1552 Sulphur Content

D-893 Toluene Insolubles/Pentane Insolubles

D-96 Water Content

Application Notes on Lubricating Oil Analyses

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