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INTRODUCTION For the value of Oil Analysis Condition Monitoring and Preventive Maintenance to be fully realised, the end user must have a basic understanding of the lubrication process and the various lubricants used. They are called on to perform many functions in today’s increasingly complex operating environments. As such, lubricants themselves have evolved to a high state of technological development to ensure correct performance and protection of the lubricated equipment. This booklet serves to provide an insight on lubrication, broken into six phases of understanding. 1. The basics of oil analysis
2.
3.
4.
5.
6.
1. Benefits of Oil analysis 2. Reading the Report 3. The Sample Description Sheet Testing of Lubricating oils. Includes tests applicable to Engine Oils, Hydraulic Oils and Drive and EP Gear Oils for Condition Based Oil Analysis 1. Moisture (water) Analysis (ASTM D6304) 2. Particle Size Distribution Analysis (ASTM D6786) 3. Retained Solids (ASTM D4898) 4. Total Acid Number (ASTM D975/D664) 5. Viscosity (ASTM D445) 6. Oxidation (ASTM E2412) 7. Nitration (ASTM E2412) 8. Wear Elements (ASTM D5185) 9. Contamination Elements (ASTM D5185) 10. Additive Elements (ASTM D5185) 11. Total Base Number (ASTM D2896) 12. Pentane Insolubles (Soot) (ASTM D4055) 13. Fuel Dilution (OL1007 – GC) 14. PQ Index (OL1029 – ANALEX) 15. Dispersancy (OL1004) 16. RULER (ASTM D6810/ASTM D6971) 17. Glycol content by GC- HSA (OL1105) Basic explanation of how lubrication works 1. Friction 2. Maintaining Lubricant Performance 3. Additives 4. Filters 5. How do we know that the lubricant is performing as required? Other Testing Requirements 1. Coolant 2. Diesel Fuel Overall summary of oil requirements 1. Engine oil requirements 2. Transmission, Drive and Hydraulic oil requirements 3. Oil Sampling Interpretation of the Analysis 1. Standard Deviation 2. Normalisation Factors
The benefit of this book is to show why it is important to undertake oil analysis and Condition Monitoring of equipment through an effective Oil Analysis Program. Such a program is applicable to any industry or environment that utilises lubrication. As the book progresses it delves deeper into the Oil Analysis Program.
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Table of contents
Page
1. The basics of oil analysis
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1. Benefits of Oil analysis 2. Reading the Report 3. The Sample Description Sheet 2. Testing of Lubricating oils. Includes tests applicable to Engine Oils, Hydraulic Oils and Drive and EP Gear Oils for Condition Based Oil Analysis 1. Moisture (water) Analysis (ASTM D6304) 2. Particle Size Distribution Analysis (ASTM D6786) 3. Retained Solids (ASTM D4898) 4. Total Acid Number (ASTM D975/D664) 5. Viscosity (ASTM D445) 6. Oxidation (ASTM E2412) 7. Nitration (ASTM E2412) 8. Wear Elements (ASTM D5185) 9. Contamination Elements (ASTM D5185) 10. Additive Elements(ASTM D5185) 11 Total Base Number (ASTM D2896) 12. Pentane Insolubles (Soot) (ASTM D4055) 13. Fuel Dilution (OL1007 – GC) 14. PQ Index (OL1029 – ANALEX) 15 Dispersancy (OL1004) 16. RULER (ASTM D6810/ASTM D6971) 17. Glycol content by GC- HSA (OL1105) 3. Basic explanation of how lubrication works 1. Friction 2. How is the lubricant forced between the surfaces? 3. Additives 4. Filters 5. How do we know that the lubricant is performing as required? 4. Other Testing Requirements 1. Coolant 2. Diesel Fuel 5. Overall summary of oil requirements 1. Engine oil requirements 2. Transmission, Drive and Hydraulic oil requirements 3. Oil Sampling 6. Interpretation of the Analysis 1. Standard Deviation 2. Normalisation Factors
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SECTION 1 1.1.
Benefits of Oil analysis
The costs are relatively small insurance premiums for optimum serviceability of equipment. Oil Analysis provides the benefits of : Extending Equipment Life. Fault Cause and Prevention Diagnosis. Condition Monitoring and Diagnosis for Warranty purposes. Enhancement to the Service Log for Better Resale Value. Improved Safety Control Effective Maintenance Scheduling and Reduction in unscheduled Downtime. Evaluation of maintenance systems. Determination of Optimum Oil Change Interval
1.2.
Reading the Report (Hitachi Probe used as an example)
The oil diagnostic analysis will provide each report with: A “satisfactory”, “monitor trend” or “take action” rating. A detailed trend analysis of the oil’s characteristics, contamination levels and histories. A set of recommendations for “monitor trend” and “take action” results. The recommendations from previous reports are included to assist with corrective action. Customers are invited to call Oilcheck to discuss any oil-specific issues contained in their reports. The sample analysis report is a composite of several key areas. The key sample information The results table The customer and equipment information Recommendations Trending graphs Did you know info and links Advertisements
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Key Sample Information
Customer and Equipment Info The Equipment details are the most crucial to the reporting process. This area dictates where the sample is from and links in previous samples to the current sample. The Operation details give information to the Laboratory to categorise the results by Oil grade and type. Did You Know 60% of failures are due to the wrong type of oil used in the compartment? The Customer Details are also just as crucial, without the correct details, you simply will not receive the report.
This section of the report shows the basic logistics of the sample, for example the Sample Number (which may be quoted in the event of any questions) ,received dates, hours on the oil and equipment, report and K numbers for the sample. The Key Sample Information Sections also includes the previous status of past samples. Results Table
Recommendations
This section of the report shows values of the specified tests. The results determine the characteristics & contamination in the oil due to wear or the introduction of contamination into the oil such as; • Moisture (contamination) • Dust and dirt (contamination) • Component wear (contamination)
A brief recommendation from the analysis performed on the sample will indicate where the potential problems or in the event of failure where the actual problems lie. The benefit of this is the previous samples recommendations are also available to assist you in what action you may choose to take. Authorised Signatory The report also contains the contact details of the person who supervised the analysis and wrote the recommendations
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Trending
Graphs
Trending is a very important part of the oil analysis system. Using the trending graphs with the analysis of your results will give you a far better indication of how the compartment you have sampled compares with the previous samples results. The results on the graphed results will be different to the results in the results table, this will occur due to a normalisation factor applied to the results (for more information on normalising please refer to the Normalisation and standard deviation Section.) In short the graphs give you the ability to compare apples with apples by adjusting the results to suit what we call standard hours (engine 200 hours & Drive and Hydraulic 500 hours.)
1.3.
Sample Description Sheet
The Sample Description Sheet can be broken down into several key areas. Page 1 • Machine Details • Oil Details • Report Recipients and Contact Details Page 2 • Compartment Codes It is ESSENTIAL that all the Information be filled out Clearly and Correctly, this will ensure the Probe data base is correct and the information you receive is also correct. A sample with the wrong or unidentifiable information is a waste of time.
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Pre-Filled or Populated Sample description Sheet
Kilometres on the equipment clearly and carefully along with any other information. 4. At the bottom of the sample description sheet there is now a facility to put in your own comments about the sample. For example “engine oil smells like it has fuel contamination please check first and let me know ASAP” the laboratory will instantly act on this comment. Further to that the comment will also be printed on your report this will help you maintain a record of your findings. What to Do 1. Check the information and change as discussed 2. The purchased Oil analysis Kit will have a blank Sample Description Sheet provided, in the bottom left hand corner you will find a K number Sticker. Remove the K number sticker, the barcode is the proof of purchase, and place on the printed pre-filled Sample Description Sheet. 3. Pack up the Oil sample as you would normally and send it to the lab as you normally would with the pre-filled in Sample Description Sheet enclosed.
The sample description sheet is also available as an attachment to your email and can also be available to be sent with the report on completion of the analysis. This service is available to all at no extra charge. Hitachi currently use this provision. This facility enables you as the customer to ensure the information is 100% correct and takes the hassle out of filling in the sample Description Sheet every time.Just a few points 1. If the sample information is not correct this is the time to change it by simply crossing out the information and writing it in the white space on the back of the form (page 2 of the Sample Description PDF) 2. Fill in any missing blanks that may be present, as stated above this is the same information provided in your last report and will be exactly the same every time you receive a report unless you change the info. 3. Use your saved time wisely and fill in the Hours or Kilometres on the oil & the Hours or
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SECTION 2
AUTOMATIC COULOMETRIC KARL FISHER FOR WATER DETERMINATIONS (ASTM D6304)
Tests Performed for Condition Based Oil Analysis 1) Moisture (water) Analysis (ASTM D6304) 2) Particle Size Distribution Analysis (ASTM D6786) 3) Retained Solids (ASTM D4898) 4) Total Acid Number (ASTM D975/D664) 5) Viscosity (ASTM D445) 6) Oxidation (ASTM E2412) 7) Nitration (ASTM E2412) 8) Wear Elements (ASTM D5185) Iron Chromium Copper Lead Tin Nickel Aluminium 9) Contamination Elements (ASTM D5185) Aluminium (contained in dirt) Silicon Sodium Potassium 10) Additive Elements(ASTM D5185) Calcium Zinc Phosphorus Sulphur Molybdenum 11) Total Base Number (ASTM D2896) 12) Pentane Insolubles (Soot) (ASTM D4055) 13) Fuel Dilution (OL1007 – GC) 14) PQ Index (OL1029 – ANALEX) 15) Dispersancy (OL1004) 16) RULER (ASTM D6810/ASTM D6971) 17) Glycol content by GC- HSA (OL1105) 2.1 Water Content by Fischer.(ASTM D6304)
Coulometric
Using a light scattering principle, particle size analysis for the various micron sizes are computed. A good Particle Size Analyser utilises a laser scanner and can detect particles from 2 to 400 microns. Results are presented utilising SAE AS4059 or ISO 4406 cleanliness level codings. An example of standard particle count ranges and the required limits areas are as per the diagram. Establishing the level of cleanliness enables assessment of the filter effectiveness for clear lubricants only. Engine oils, due to the dark opaque nature obtained during use, cannot be analysed in this manner.
PARTICLE SIZE ANALYSIS USING LASER EXTINCTION ASTM D6786
Karl
Contamination of an oil based lubricant by water can damage the metal-to-metal surfaces that the lubricant is designed to protect. The local frictional effects within the lubrication system be it hydraulic, engine, transmission, etc, can cause temperatures in excess of the boiling point of water which would in effect cause steam cleaning of the oil away from the surfaces. The boiling of the water or moisture can also promote oxidation in the oil and be blamed for corrosion and poor lubrication on the metal surfaces. Moisture can be sourced from the atmosphere when the compartment is cooling down, engine blow by gasses and coolant leaks.
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2.2 Particle Size Distribution Analysis.
2.3 Retained Solids Content in Hydraulic Oils. Retained or Total solids content of hydraulic oil is also determined by filtration to 1 micron. By passing the oil through a filter membrane all particles larger than 1 micron are retained. The filter is then weighed and a weight of the filtered material will give us through a calculation the Retained solids content. Various applications of hydraulics will dictate acceptable solids content but usually retained solids content in excess of
500 parts per million by weight (0.05 %) is considered unacceptable and will indicate that the oil filtration system is either by-passing or ineffective and requires attention. 2.4 Neutralisation Number
Number
or
Total
Acid
The Neutralisation number of an oil is calculated as the amount of acid OR base necessary to make the lubricant chemically neutral. The main Neutralisation Number value used is the Total Acid Number (TAN) and this is a measure of the oils acidity expressed in the same terms as the TBN value (2.11).
TOTAL ACID NUMBER (ASTM D664) AND TOTAL BASE NUMBER (ASTM D2896) ANALYSIS BY AUTOTITRATOR
2.6 Oxidation Lubricants will oxidise when exposed to air or products of combustion in engine oils. The oxidation level can be determined using infra-red signatures of the lubricant and any increase in oxidation from the “new oil” value is a measure of how the oil is standing up to the harsh environment in which it must operate. The smaller the number quoted in the report, the lower the amount of oxidation. Conversely a high oxidation level will indicate the likelihood of the oil thickening and eventual failure of the lubricated component due to a lack of effective lubrication. In applications where the lubricant has only minimal exposure to air such as sealed gear compartments and hydraulic systems, the oxidation level would not be expected to increase to the same extent as occurs in engine lubrication. As such, the lubricant life is generally longer in these compartments than in engines. Oxidation preventing additives, called oxidation inhibitors or anti-oxidants, are generally incorporated into most formulations to counteract the effect that oxygen and heat, the major cause of the oxidation, have on the lubricant. 2.7 Nitration
2.5 Viscosity for Liquid Lubricants. Viscosity measurements of new and used oil characterise the lubricant as to its grade. Viscosity grades are listed as SAE or ISO. The thickness of an oil is graded and calculated as the Viscosity in mm2/s (Centistokes). ISO oils are specified at 400C. SAE oils are specified at 1000C. The Viscosity Index of the lubricant is a calculated value based on the viscosity values at 400C and 1000C. Again, like the viscosity value itself, the VI can be used to characterise or confirm the identity of a lubricant as mono-grade or multi-grade. AUTOMATIC CANNON VISCOSITY DETERMINATIONS AT 40 AND 100oC (ASTM D445)
A major component of air is the gas Nitrogen. In extreme cases, it can react with the lubricant and oxygen to produce an effect called Nitration. In compartments such as gear boxes or hydraulic systems, the nitration effect would be minimal since the exposure to air and high heat (>300 deg C) is rarely encountered. However, in the combustion process in engines, the temperatures exceed 600 degrees C. Oxygen, Nitrogen, fuel and lubricating oil combine to form nitration products including nitrogen oxides which by and large are exhausted to atmosphere. Some can however, find its way past the rings and into the crankcase. Once in the crankcase the nitration product will combine with soot, oxidation and sulphation products The nature of the soot (carbon formed by incomplete combustion of the fuel) is such that nitrogen oxides and nitration products are absorbed and retained in the sump oil. Again, as in the case of oxidation, the infra-red signature of the lubricant shows the extent of presence of nitration. As would be expected, the value for a new oil is low and would reflect the relatively small amount of nitrogen based products formulated into the lubricant as anti-oxidants. As the soot content of the used oil increases, so does the nitration level.
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AUTO-FOURIER TRANSFORM INFRA-RED ANALYSIS ASTM E2412
2.8 Wear Elements Iron can be present as fine particles produced by abrasion or wear, but also as iron oxides associated with the presence of water or a corrosive reaction to additives. Iron generally comes from the liners in engines or from hydraulic cylinders, pumps, lines and reservoirs in hydraulic systems, and from planetary gears and carriers in final drives and differentials. Chromium is a very hard metal wear particle produced by engine piston rings. Chromium readings indicate that something harder than it is present, namely silica or alumina (sand). It can also be produced in new engines during the run-in period, Chromium in hydraulic systems is typically from valve spools or cylinder rods; it is also produced by harder abrasives. Chromium is also found in final drive and differential bearings. Copper is a soft metal from bronze alloys that are present in engines, hydraulic pumps, differentials, final drives, and in cooler cores. In engines, its presence could be caused by a coolant core or water pump leak, but also from thrust washers in the camshaft, rocker arm or piston wrist bushings. When present with Glycol (in association with potassium and sodium) it could be coming from the oil cooler. When it is associated with lead and/or tin, but without glycol traces, it is an indication that it is being sourced from the bearings/bushings. New oils can promote high copper generation during run-in periods, ranging from 10 to 100 parts per million or more, Larger generation of copper is typically triggered by water, silica (dirt), high temperature operation and most importantly, by additive incompatibility from fluid mixing. Copper is also found in final drives equipped with park brakes and slip spin/diff lock differentials, or from thrust washers. Aluminum is a wear element that generally comes from pistons in engines. High aluminum
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associated with silica can indicate dirt. If aluminum is found in hydraulic systems, it could generally be assumed it comes from dirt ingestion. Aluminum in final drives can only be dirt or sand. Some bearings can include aluminium (eg refrigeration compressor bearings and some main engine bearings) Tin is a metal used in soft alloys of bronze in combination with lead. It is generally present in small amounts in hydraulic pumps. However, when tin is present in engines, it is usually associated with lead and copper to indicate bearing wear. Lead is a very soft metal used in alloys in combination with tin for engine bearings and bushings. Lead is present in hydraulic pump alloys as well. Highly oxidized engine oils attack bearing material, which increases lead readings. Nickel it is seldom seen in oil analysis but when it shows up it is an indication of turbocharger cam plate wear. Titanium is not a typical wear metal present in oil analysis from construction equipment. Some traces are possible from some alloys. Titanium in the form of titanium oxides can be found in oil analyses as a contaminant from operation in bauxite mines. Some industrial equipment reservoirs have in the past been painted. As titanium dioxide is used as a paint filler, titanium in oils may indicate break-down of the paint allowing particles to be present in the oil. 2.9 Contamination Elements Silicon is the principal component of dirt and it is found in its natural and oxidative form as silica. It is harder than any metal used in mobile equipment and can scratch hard surfaces easily. In new engines, its presence could indicate liquid silicon material used as sealant during assembly. It typically washes out after first oil change. Silica (the oxidative form of silicone) appears in nature associated with alumina in a typical 5 to 1 ratio. Silicon up to approximately 10-15 ppm may reflect presence of silicone oil based anti-foam additive. Aluminum is generally present in association with silica in a 1 to 5 ratio and enters together with dirt. It enters the system in its oxidative form as alumina, or in combination with silicon as aluminium silicate and it is extremely hard. Aluminum is the most abundant metal in the world. Potassium may be present in coolant formulations and it is not an additive for engine oils as such, although some small readings of about 1 to 2 parts per million (ppm) could sometimes be present. When combined with other elements such as
sodium, molybdenum or boron it is an indication of coolant contamination. Sodium may also be present in coolant formulations but also in many salts, or seawater. In small amounts it may be found as an additive, however, if its presence is associated with potassium and/or boron and/or molybdenum it is a generally an indication of coolant contamination. 2.10 Additive Elements Boron is an EP (extreme pressure) additive but it is also found in coolants. Boron without the presence of potassium is an indication of an additive. Barium as barium petroleum sulphonate can be used as a detergent in oil formulation as well as corrosion inhibitors. Calcium as calcium petroleum sulphonate is a detergent. It cleans carbon deposits from engines and acts as a corrosion inhibitor and dispersant. When burnt, calcium additives have an ash content of generally >1% in engine oil formulations Magnesium as magnesium petroleum sulphonate is also a detergent that leaves generally < 1% ash. It reacts with sludge and varnish to neutralize them and keep them soluble. Molybdenum may be present in some oil formulations as a solid lubricant additive (molybdenum disulfide) and may be used as an additive in grease. Soluble molybdenum additives are added to formulations in some cases also. Sodium is found as an additive in some instances as a detergent. Phosphorus is found in extreme pressure (EP) as well as in anti-wear /anti-oxidant additives and friction modifiers in engine oils, hydraulic fluids and gear oils. Sulfur is found in extreme pressure additives in combination with phosphorus. Zinc is part of ZDDP (Zinc Dialkyl Dithio Phosphate) additive that acts as an anti-wear, anticorrosive and anti-oxidant additive.
Metals are analysed using an instrument called Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES). Argon gas is excited electrically and produces a plasma with a temperature of between10,000 and13,000oC into which the sample is sprayed. Elements all have specific wavelengths the data collected is allocated to each of the wavelengths selected to give the metal content in parts per million. 2.11 Total Base Number for Engine Oils. Corrosion inhibitors are added to counter acidic effects on metals. In engine oils, reserve alkalinity is included in the formulation to neutralise acids formed by combustion. This is reflected by the Total Base Number (TBN) of an engine oil. The TBN value of an oil is calculated from the amount of acid that is required to counteract its basic characteristics. The TBN is expressed as the Equivalent mass in milligrams (mg) of potassium hydroxide (KOH) per gram of the oil. 2.12 Pentane Insolubles or Soot Content. The laboratory can also monitor the amount of detrimental soot contained in an engine oil by filtration of the material insoluble in a solvent called Pentane. This filtration is at 0.8 micron in size, on the basis that material less than 0.8 micron would not be likely to cause problems. The material removed is weighed and expressed as a percentage of the oil. Values below 0.35 % by weight are usually considered acceptable in the normal service interval for a diesel engine. Levels of at or above 0.35 % by weight indicate a detrimental effect on the oil and reflects “elevated sooting” which may be caused by poor ring seal. Some of root causes of these detrimental effects could be excessive periods of idle running, cold running, or fuel washing the oil seal away in cases
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of defective injectors and this in turn could be evidenced by increasing viscosity and depletion of anti-oxidant and dispersant additive. An increase in viscosity at 100oC can lead to deterioration in the lubrication efficiency which can effect correct operation of bearings, cams/lifters. Consideration of change-out of the oil at this stage would be recommended depending upon other results of analysis. The soot content can be checked as TOTAL SOOT by using a technique known as THERMOGRAVIMETRIC ANALYSIS which is commonly referred to as TGA Soot.
2.14 PQ Index
2.12 Fuel Dilution by Gas Chromatography.
Severe Wear - large particle occurrence which may reflect presence of metal particles due to fatigue fracture or pitting of the metal components. This production of large metal chips can in turn induce enough wear to cause further disintegration and rapid onset of failure.
Fuel dilution in an engine oil can be caused by several factors. Determining the extent of the contamination by fuel by accurate means is essential for the effective monitoring of engine performance. Gas Chromatography can precisely determine the fuel dilution in a lubricant to as low as 0.2% v/v by separating and quantifying the actual fuel content. Other methods employed in the past included approximation from flash point values to an accuracy of + or - 4%. In instances where the 2 stroke engine of the Detroit type are used, the 4% margin can be the difference between engine failure or not. This is due to excessive fuel in the oil which can have the effect of thinning it out to an unacceptable level. Although indication of fuel dilution can be determined from viscosity values in some instances, “sooting”, another product of incomplete combustion of the fuel, can have a thickening effect of the oil and thereby disguise fuel dilution problems.
When wear occurs in equipment, the particles resulting from the wear process can be of several types, namely: Normal Wear - small wear particles due to typical welding/breaking cycle as outlined in earlier discussions Significant wear - medium sized particles causing gouging of metal and resulting in larger than normal particles being generated. These in turn become the cause of even larger particle generation
Since most of the metal fragments referred to in the above wear scenarios are iron in nature, the effect of the particles on a magnetic field can be used to detect the type of wear. Small fragments would, as expected, have the least effect on a magnetic field, while the large chips of iron would be expected to have a large effect. The instrument used in the laboratory for determination of Particle Quality (PQ), measures the effect of the wear particles on a magnetic field. When calibrated on known standards, an index or relationship number can be produced and from this the criteria for satisfactory, significant and severe wear can be determined and reported as the PQ Index. 2.15 Dispersancy. Dispersant additives are incorporated in engine oil formulations to ensure that minimal accumulation of contaminants that result in sludging will occur. Sludging is the combination of mainly moisture and soot or wear debris from the engine. It can adversely affect the engine operation through filter plugging, deposition on moving surfaces and by thickening of the oil to an extent that incorrect lubricant supply will result. Dispersancy is simply assessed using the “blotting paper” test and is adjudged as: GOOD Satisfactory dispersant properties in oil. FAIR Unsatisfactory dispersant properties. An oil change is required. Normally, other parameters of analysis will be adverse.
PE Clarus Gas Chromatograph
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POOR Totally unacceptable or no dispersant properties in oil. Oil in this state will be considered overdue for change and will also be reflected in adverse test results in other areas.
2.16 RULER measurement of Anti-Oxidant Content Oils, with the exception of EP Gear Oils, in general have one or more Anti-oxidants (AO) included into their formulation. AO’s are sacrificial additives in that they are the first to be consumed in their function of protecting the equipment that is lubricated and more specifically the oil itself. It stands to reason therefore that monitoring the AO level in an oil (or grease) can provide data that permits accurate determination of how much life the oil still has. This saves money to maintainers by using the oil until it can no longer satisfactorily protect the lubricant (usually when the RULER AO value is less than 30% of the new value) which from past experience may be significantly longer than the recommended service change-out. If the AO levels are being severely depleted in a shorter time frame than expected, then proactive maintenance to rectify a potential problem can also be reflected in saving by the reduction of unscheduled down-time.
vapours collected are measured by gas chromatography. Another method by Fourier Transform Infra-Red (FTIR) analysis is unreliable and subject to many interferences from oxidation products in the oil as well as moisture.
The RULER (Remaining Useful Life Evaluation Routine) uses a small amount of the in-service lubricant reacted with a special solvent based chemical and then compared to a sample of new lubricant of the same type and grade reacted with the same type of special solvent based chemical. The amount of remaining active Anti-oxidant additive compared to the new sample give the % of Remaining Useful Life (%RUL) 2.17 Glycol by gas chromatography method Glycol contamination in an engine due to coolant leakage is a major problem and requires accurate and reproducible assessment. One method is by a process called Head Space Gas Chromatographic Analysis. A sample of engine oil is heated above the boiling point of glycol (180-200oC) and the
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SECTION 3 A BASIC EXPLANATION LUBRICATION WORKS
OF
HOW
Lubrication A dictionary definition of lubrication is “...the process of smearing with oil, grease, etc to reduce friction”. Probably as good, a definition as you might find from conventional sources, but What is Lubrication? What properties are required in a lubricant? What can affect these properties and how can these effects be monitored to maximise lubricant and equipment usage? 3.1. FRICTION Friction is an accumulation of Forces that tend to prevent motion between surfaces that are designed to move relative to each other. The extent of these frictional forces directly relates to the load placed on the surfaces. The smaller the Area Of Contact , the greater the effect of the Load per square millimetre On rough surfaces, this is further increased. For example, consider the bearings in an internal combustion engine, mating gear teeth in a gearbox or the piston of a hydraulic ram. In each of these cases, surface roughness is a critical factor. A simple example of the effect of surface roughness on motion is to place two files, one on top of the other on a bench with a load on top of them. Try to slide the top file out from beneath the load. It is difficult to achieve the desired motion. If you take a very close look at even the “smoothest” surfaces that would be encountered in engineering applications, each surface would consist of microscopic high and low spots. The metal-to-metal contact would only be on these high spots (called asperities) with the consequent point loading similar to the “files example”. Point loading leads to a High Coefficient Of Friction. viz. look at the ball bearing surface. Under normal vision the ball looks, and feels, very smooth. A 100X magnifications shows that the surfaces shows “grooves on the surface which look more pronounced at 200X magnification. The edges of the grooves are the high spots (asperities) and when mated with corresponding surfaces of the inner and outer races with their asperities due to surface roughness, friction can occur leading to heat and wear.
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X 100
X 200
By adding motion, the asperities on the surfaces would generate enough heat to weld, the continued application of the force would cause the weld to stretch and break leaving new, similar asperities generated on the surfaces. Metal particles can also break off which can then act as an abrasive leading to an accelerated process of “wear”. It is obvious that the effects of these surface peaks must be reduced. Lubrication choice is critical to avoid asperities coming into contact with each other, hence lowering friction and decreasing the amount of potential. ADHESIVE WEAR WELD FRACTURES WELD OCCURS
AND GENERATES PARTICLES
ADHESIVE WEAR DEBRIS FROM A TRANSMISSION 120X MAGNIFICATION
There are three main types of friction-reducing materials and these can be used singularly, or in combination as the application requires They are: LIQUIDS SEMI-SOLIDS SOLIDS The liquid type material is generally employed where it can be easily contained and relatively protected from external contamination. These include Oils (vegetable, petroleum, synthetic), or other fluids such as water or solvents in
combination with additives. For simplicity only, consider all of these liquid lubricants as acting in a similar manner.
This process Lubrication.
is
known
as
Hydrodynamic
A liquid can be considered as consisting of “slippery balls” that are able to slip and slide over each other but are nevertheless “stuck” together. If the size of the balls can represent the thickness of the lubricant (viscosity), the method of providing a lubricant film can be explained.
0000000000000000000000000000 0000000000000000000000000000 0000000000000000000000000000 0000000000000000000000000000 0000000000000000000000000000 0000000000000000000000000000
By forcing the “balls” between the surfaces which are to move relative to each other, the asperities effect can be overcome to varying degrees depending on the “size” of the “balls”. If the lubricant is too thin, the balls cannot fully support the load and keep the surfaces apart sufficiently to permit unimpaired motion. So if one of the two surfaces is harder than the other, it is logical that the softer material will be gouged away by the asperities of the harder material. Microscopic particles of the worn material will be picked up by the lubricant and carried around the system. Better surface separation can be achieved with a thicker lubricant made of bigger “balls” that are still small enough to slide over each other while still being in contact with the surfaces at all times. The surfaces are constantly “wet” with lubricant. Even thicker lubricants can maintain a satisfactory surface separation but the “balls” may be too large to maintain constant surface “wetness” during motion. With a fixed clearance dictated by the applied load to the surfaces, the “balls” cannot squeeze into the gap. 3.2. HOW IS THE LUBRICANT FORCED BETWEEN THE SURFACES? A lubricant film will adhere to surfaces upon which it comes in contact. This is referred to as Boundary or Thin Film lubrication. It is the main source of lubrication in equipment upon starting from rest. In this case the asperities can and will make contact and wear occurs. As the relative motion between the surfaces increases, particularly rotational motion, the boundary lubrication film is increased as the lubricant is forced between the surfaces.
The fluid film, which develops pressures sufficient to carry the load and hence permit motion, is increased due to the “wetted” surfaces dragging more “slippery balls” (molecules) between the surfaces when these commence rotating. A situation will be arrived at which the maximum film thickness is achieved. The oil molecules can be considered as a wedge that continually supplies replacement lubricant to maintain this film thickness. The faster the rotation, the greater the separation un til a balance is acheived. Conversely, as the rotation slows down the film diminishes. The same principle applies to meshing gears. A term “Molecular Shearing” should be mentioned at this point. The forcing of the lubricant molecules between the surfaces causes a strain on the molecules which are primarily long chain hydrocarbons. If the strain applied is great enough, usually associated with elevated temperatures,, the molecule can break. With normal paraffin oils the Shear Stability is good. The oil molecules possess great bond strength. With Viscosity Index (VI) improved oils however, this is not necessarily the same. VI improvers are generally very large molecules, considerably larger than oil molecules. They may be considered as being “coiled up” in the rest position. Under load and heat, the molecule uncoils and stretches initially leaving it weakened and further loading can cause the molecule to “shear” into smaller coiled up molecules. This results in a thinner oil with all its consequences concerning boundary layer thickness mentioned earlier. It follows that VI improved oils may not necessarily be a good option in areas of high shear potential such as gear boxes and transmissions. Consider now the semi-solid lubricant case. Grease is the most common semi-solid lubricant and is mainly comprised of oil that has been artificially thickened with soap or clay earth such as bentonite. Greases are generally employed
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where problems associated with containment of a liquid lubricant are encountered. Open gear lubrication can also incorporate “tackifiers” to make the lubricant adhere to the gear teeth during their operation. The “ball” analogy previously described for liquid lubricants is also applicable to semi-solid lubricants. The solid lubricant method of friction reduction entails “filling-in” the surface imperfections with a material that has a good load bearing capability but can easily shear when motion is commenced. Consider again the “file” example. Place two plastic sheets between the files and relative motion of the files is considerably easier to achieve. Typical examples of such solid lubricants are Molybdenum Disulphide, and Graphite. Both of these materials have structural characteristics that can be portrayed as a deck of playing cards. The deck can support a considerable top load, while motion can still be achieved due to the low shear strength of the material. Molybdenum Disulphide has a load carrying capability greater than 5 times that of steel and yet has a very low shear strength that permits motion by layers of the Molybdenum Disulphide sliding over each other while supporting the load. Coatings such as these can be applied by bonding processes for completely dry lubrication applications, or they can be and are successfully incorporated into formulated liquid lubricants that combine the attributes of both solid film and liquid lubrication. Mention should also be made of the introduction between the rough surfaces of plastic type materials such as “Teflon” that have applications in some instances. Extensive research has been carried out in liquid lubricants, including those that incorporate the advantages of solid lubricants. The main thrust of such research has been in establishing the correct lubricant thickness under varying environmental conditions. Accordingly, recommendations of lubricant Viscosity (the term used for lubricant thickness) should be adhered to rigidly. While the viscosity of the lubricant at one temperature may be satisfactory to maintain the desired clearances, it is the lubricant’s ability to maintain these clearances at higher temperatures that determines the lubricant’s suitability. The variation of the viscosity of a lubricant with temperature is called its Viscosity Index (VI). An oil with the least amount of variation of viscosity with temperature has the highest VI while conversely the greater the variation the lower the VI. In instances where wide temperature ranges can be experienced such as internal combustion
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engines, the VI is an important parameter. VI of around 100 is indicative of a paraffin base which is oxidation resistive. Lower VI’s can be tolerated where the operating environment is not subjected to the same amount of temperature variation or possibility of external contamination such as in a gear-box or hydraulic system. However, for the stability factor among others, paraffin base oils are preferred for these applications. Fuel Dilution in engine lubricants can severely affect viscosity measurements and hence will also affect VI. The greater the fuel dilution level, the greater the effect on viscosity. Moisture contamination can also affect the viscosity values to an unpredictable extent in some severe cases. This will also affect VI. Solid contamination such as soot will be encountered in most engine operations. A small amount of soot (or Pentane Insolubles) will not have any undue effect on the oil viscosity but as this level increases the viscosity and VI can be rapidly changed. It should be noted that the effect of soot is more pronounced at higher temperatures than at low. If lubrication was only concerned with reducing friction by selection of correct lubricant viscosity and VI, the problem would be relatively clear cut. However, in the service life of the lubricant other factors are involved which cause varied oil degradation. Some of these factors include: Dust particles that by-pass seals & air filters. Varnishes and gums formed in fuel combustion. Water formed by fuel combustion and condensation. Wear metals due to aspirate abrasion. Burnt lubricating oils scraped from the cylinder wall linings. Fuel and carbon particles from incomplete combustion. Sulphur and nitrogen oxides from combustion of fuel. Organic acid formation by oxidation of oil during operation. Trapped air due to agitation. Coolant leakage through leaking or cracked gaskets, heads or liners. While the majority of these contaminants generated by fuel combustion are exhausted through normal operation, a certain proportion will find its way past the rings and into the crankcase and monitoring this may enable appropriate early warning of severe damage to be made. Hydraulic and transmission oils do not have such a problem of massive assault by possible external contaminants, but some of the above are most
pertinent. Moisture by condensation caused by systems “breathing” moist air on cooling is a major problem in hydraulics, transmissions and drives. The discrete particles of water can vaporise due to operating temperatures induced by fluid film and metal to metal friction and force lubricant away from the surfaces requiring lubrication. It is also a cause of corrosion in the compartments. Dust ingress through breathers and poor seals is also damaging due to its abrasiveness. Accurate monitoring of these contaminants is the key to planning maintenance effectively. 3.3. ADDITIVES To counteract the majority of ill-effects that contaminants cause, additives are incorporated in the oil formulations. 3.3.1 Detergent additives clean deposits from inside engines while the dispersant additive keeps what is cleaned separated to avoid “sludging”, particularly when moisture is present. 3.3.2 Anti-Oxidant (AO) additives are widely used in oil formulations to provide chemical protection to oil wetted surfaces as well as providing protection to the base oil of the lubricant to permit it to continue its major function of carrying the additives to the areas that need them and maintaining the fluid film gap between the moving surfaces. 3.3.3 Anti-foaming additives prevent bubble persistence that may cause lack of lubricant to critical locations. 3.3.4 Anti-wear additives chemically treat the metal surfaces and make them “slippery”. 3.3.5 Pour Point Depressants In some instances, cold temperatures can be experienced that could freeze lubricants, consequently an additive is incorporated that enables the oil to pour at low temperatures. 3.3.6 Corrosion inhibitors are added to counter acidic effects on metals. In engine oils, reserve alkalinity is included in the formulation to neutralise acids formed by combustion. This is reflected by the Total Base Number (TBN) of an engine oil. 3.3.7 Oxidation inhibitors are also necessary to prevent deterioration of the lubricant due to the action of moisture, air and temperature on it. FUEL SULPHUR EFFECT ON ENGINE OILS Mention should also be made of the effect that the sulphur content makes on the TBN of the oil. Sulphur is becoming less prevalent in engine fuels due to the environmental concerns of the exhaust emissions from diesel fuelled engines. The sulphur removal by legislation at the refinery has effectively reduced the sulphur level to 50 parts
per million (ppm) (0.0050%) and a sulphur level of 10 ppm or 0.0010% has been mandated. for 2009. . The effect of sulphur oxides from combustion entering the crankcase area is, therefore, greatly reduced and as such the conventional diesel oil TBN value of up to 8 is quite suitable in providing the required protection in a correctly operating engine. When the TBN has dropped to 50% of its original value, the lubricant’s reserve alkalinity is considered to be reduced to an unacceptable level requiring that the oil be changed. This 50% reduction, by virtue of the lower fuel sulphur, will rarely be met in modern diesel engines. A better gauge of how long the oil should remain in service is by monitoring of the AO level in the oil by RULER. In short, the modern lubricant has been designed and formulated to meet the harsh environment of modern equipment. Contaminants, including most after-market additives can “Unbalance” the lubricant and can result in less than optimum performance in its duty. 3.4.
FILTERS
Removal of contaminants is necessary to extend the service life of lubricants. This is achieved by filtration. There are many types of filters on the market and most employ cellulose or paper elements as the filtering medium. Some of these mediums claim filtration to 0.1 micron. Cotton is also used in by-pass filters with filtration rates of 25 microns being generally quoted. External “kidney-loop” filtration has become a viable means of maintaining a clean compartment and extending the life of the equipment lubricated as well as the lubricant itself. All filters will reduce the solid matter contamination to the appropriate micron size without detriment to the properties of the lubricant, that is they cannot remove the additives from the oil formulations. Even polymers employed as viscosity index improvers and tackifiers will pass through the filters as they are dissolved in the oil base. A good rule of thumb to use when considering filtration is: “If It Can Be Removed By Filtration It Shouldn’t Be There”. A detergent/dispersant additive in an engine lubricant formulation works Physical Attraction to contaminants such as particulate matter and water. When a filter medium stops particles of a size greater than its rated size, some detergent/dispersant may be initially, temporarily held back due to its adherence to the particle. However, this adhesion may be broken by the oil flow through the filter, leaving the particle
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entrapped in the medium. The detergent is then free to continue its function.
CHEMICAL properties of the lubricant e.g. TBN or TAN value,
With modern engine lubricants, the filters will halt only particles of size greater than its micron rating due to the strong concentration of dispersancy resulting in good adherence to particulate matter. Ideally, a filter rated at 5 microns or less is required to protect the 5-10 micron fluid film thickness normally encountered in the lubricated region. However, this fineness of filtration may cause oil flow problems and these filters are generally placed in a by-pass mode with the normally rated 25 micron filter left in full flow. Protection of a system from premature wear can be attained by filtering out particles of as small a size as possible and should be exercised where appropriate.
AO levels (%RUL) to ensure proper levels of protection are maintained LEVEL OF CONTAMINATION of the lubricant e.g. Water content, Dirt content, Acidity Values
As filtration of Hydraulic, drive and Transmission oils is also utilised, the life of filters and lubricants should also be monitored for effective control of maintenance in these compartments. The work of the NASA programmes for fluids used in aircraft applications has provided the general lubricant market with a Cleanliness Rating Level which can allow decisions to be made about oil cleanliness and filter effectiveness. ISO (International Standards Organisation) codes have also followed suit. Society of Aerospace Engineers Aerospace Standard (SAE AS) 4059 particle size analysis levels up to 10 are generally acceptable for normal operation in most applications of Hydraulic and Transmission Fluid. Greater than level 10 could indicate that the filters are blocked and should be replaced. Continued usage at levels greater than 10 could result in premature wear in the respective areas. For drive applications, the cleaner the system the better but achievement of the levels expected of hydraulic systems and transmissions is difficult. Ideally, Condition Monitoring Programmes should include Particle Size Distribution analysis for Hydraulic, drives and Transmission systems that incorporate forced lubrication and filtration. 3.5. HOW DO WE KNOW THAT THE LUBRICANT IS PERFORMING AS REQUIRED? To analyse a lubricant for all the additives it contains is not an easy task even in the unused state. Of more importance is to analyse the lubricant to check the: PHYSICAL properties of the lubricant e.g. viscosity and viscosity index
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EXTENT OF WEAR METAL PRODUCTION e.g. Iron, Copper, Lead, Aluminium, Chromium, Tin etc. The individual analysis of a lubricated compartment will provide a significant amount of information concerning the operation of the lubricant and more importantly, the condition of the equipment lubricated. If conducted on a regular basis, Trends will appear that will typify individual items of equipment. Trends established for “normal” operation are a useful guide in interpretation of results. Actual trends developed from several (at least three) analyses on the same equipment compartment will establish criteria for “Normalcy” of that specific compartment. For this important reason, accurate timing, top-up quantities, lube type and operating location information is essential in providing you with an effective service. Although the lubricant is still considered the cheapest replaceable item in large plant and equipment, the oil has a finite cost, both to purchase as well as dispose of, and to obtain full value, the oil should be changed out only when it can no longer effectively protect the oil and the moving surfaces. The additive in the oil formulation that provides this protection is the ANTI-OXIDANT which can be measured using RULER.
RULER.
4. OTHER TESTING REQUIREMENTS 4.1. Coolant A significant proportion of engine failures are attributed to the cooling system and therefore it is prudent to analysis the coolant from the cooling system. Other compartments are, in some cases, cooled and analysis of this coolant should also be considered by the maintenance planners. Coolants are tested for Glycol Content – A measure of the glycol content in the coolant to ensure the anti-freeze capability is intact. This is analysed using Refractive Index and is generally in the range of 25 and 55%. pH Value – A measure of the acidity of the coolant which typically should be between 8 and 11. Total Dissolved Solids – Salts and corrosion products are dissolved in the coolant and will increase during the service life of the coolant. There can come a time where the coolant is saturated and deposits start occurring in the system. This can lead to localised hot spots as the hardened sludge is a poor conductor of heat. Additionally, pitting corrosion can happen under this scale or hardened deposit which can rapidly cause holes in liners. Values greater than 3% dissolved solids can cause problems. The Total Dissolved Solids content is determined by
evaporation of filtered coolant and weighing the residue. Metals – Coolants are checked to determine the metal content by ICP-OES as for oils. Of particular interest are the Calcium and magnesium contents as these contribute to scale formation and are present in the water content of the coolant. Corrosion elements such as copper, from radiator cores, lead from water pump bearings, iron from crankcase and cylinder liners and aluminium from some engine heads should be monitored regularly to ensure mo abnormal levels of corrosion is occurring which may be due to low pH values, other introduced corrosive agents or depleted anti-oxidant and corrosion inhibitors. IONS – Chloride ions from water and sulphate ions from depleted sulphite antioxidants and calcium ions from water hardness can combine to form scale in conjunction with other metals. Other ions that are monitored on a regular basis are the additives in the coolant such as nitrate, nitrite borate, silicate and molybdate salts of sodium and potassium that protect the system from oxidation and corrosion. These contamination ions are determined using an Ion Chromatograph which identifies the type and quantity of each of the ions using electrochemical procedures against standards. Caution levels of contamination ion levels are Chlorides Sulphate Calcium
100 ppm 50 ppm 5 ppm
Chlorides can cause corrosive products while calcium and sulphate form insoluble salts that are the pre-cursor to scale formation.
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ION CHROMATOGRAPH FOR COOLANT ANALYSIS
4.2. Diesel Fuel Tests Appearance – The appearance of the diesel fuel will give an immediate indication of the cleanliness of the fuel. Having shaken the fuel sample it is then visually observed for signs of solid contamination and free water. Any haziness indicates some contamination which is then quantified in further testing. Colour – Diesel fuel has a specified colour according the colour standards at the laboratory. Diesel fuel typically has a colour of 1.0 or less when new but as it ages the colour can darken to greater than 3.0. This does not necessarily mean that the fuel is unusable, but does require characteristic testing to determine its suitability or otherwise for use in diesel engines. Density – The density of the fuel is specified to be between 0.82 and 0.85 Kg/litre which is deemed to be the range within which the fuel power is optimised when aligned with the Clean Air Act for particulates and noxious gaseous emissions. Distillation – Diesel fuel is a mixture of aromatic, olefin and paraffin hydrocarbons that are designed to, after ignition, burn progressively to deliver the power over the ignition component of the fuel cycle. The progressive burn evens out the combustion process and does not put too great a stress on the engine components compared to an instantaneous combustion of all the fuel. Accordingly, a good quality check on fuels
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is to perform the distillation of the fuel to verify its composition. Contaminants such as solvents, kerosene etc will show up as abnormalities in diesel fuel distillation testing. Water - Water affects lubricity in injector pumps and injectors if it can get by the fuel filter. Water, in sufficient quantity can block fuel filters and starve the engine of fuel. If allowed to reside in bulk tanks, particularly marine applications, the water fuel interface can promote growth of bacteria and fungus which again can cause rapid fuel blockage and in some cases corrosion in the fuel system itself. Checking the fuel for water content is essential for assessing fuel quality and the value typically should be no more than 200 mg/l (ppm) for efficient engine running. Retained Solids – Solid contamination can be present in fuel system in the form, of scale from storage tanks or dust ingested through breathers. While the vast majority of solids would be captured by filtration, the presence of solid matter of any more than 100 mg/l (ppm) may be detrimental and if present should be filtered out using external filtration. Microbiological Activity - The bacterial and fungal infestations mentioned above should be checked frequently to determine whether or not the fuel requires treatment with a biocide. There should be no fungal growth results for satisfactory condition and only slight amount of bacteria permitted (usually airborne and not resident in the fuel as such). Flash Point – The flash point of diesel fuel is specified with a minimum of 61.5oC but is typically in the range of 70 oC to 80 oC. If higher than 80 oC the fuel may be harder to ignite, and if it less than 61.5 oC the product would have to be classified as dangerous goods. Cetane Index – An indicator of fuel ignition delay is the Cetane Index. Ignition delay is the time period elapsed from injection of the fuel to the start of ignition. Cetane Index is calculated from density measurement and the recovery temperatures at 10% recovered, 50& recovered and 90% recovered during the distillation test. The higher the Cetane Index, the shorter the ignition delay. Conversely the lower the Cetane Index the longer the ignition delay which can lead to
rough running of the engine and increase the likelihood of sludge formation due to presence of unburnt or partially burnt fuel. Cloud Point – Diesel fuel will freeze into a gel-like substance if the temperature falls too low. A precursor to this gellification is called the Cloud Point which is the temperature at which the fuel commences to go hazy due to the formation of the crystalline structure of some fuel components which start to fall out of solution imparting a “cloudiness” to the fuel. It is important to monitor this characteristic if there is a possibility of encountering low temperatures. Biodiesel Content – With the push to utilise renewable fuels, the introduction of biodiesel into diesel fuel is underway. The presence in the fuel of up to 20% biodiesel is being recommended in some circles, however, there is currently no specification that covers this type of fuel (called Diesel B20). It has been established that 5% biodiesel will not affect the diesel fuel and should meet all the diesel fuel specifications. Biodiesel will burn effectively.
SECTION 5 – LUBRICANT REQUIREMENTS
5.1
Engine lubricant must:
1. Clean engine surfaces to prevent build-up of contaminants. 2. Disperse these contaminants. 3. Provide correct lubrication film thickness throughout the temperature ranges encountered to lubricate and remove heat from the sites of potential wear. 4. Provide a slippery coating of anti-wear material on moving surfaces. 5. Counteract corrosive materials in the oil. 6. Rapidly eliminate the possibility of air entrapment caused by agitation or in some cases cavitation. 7. Remain fluid at normal cold start conditions.
5.2
Transmission, Drive or Hydraulic lubricant must: Provide correct lubrication film thickness throughout the temperature ranges encountered to lubricate and remove heat from the sites of potential wear. Provide a slippery coating of anti-wear material on moving surfaces.
Counteract corrosive materials in the oil. Rapidly eliminate the possibility of air entrapment caused by agitation or in some cases cavitation. Remain fluid at normal cold start conditions. By constant monitoring of the “life blood” of the compartment, adverse changes can be detected early. In many instances it can permit avoidance of a catastrophic failure by attending to a less major problem. 5.3 SAMPLING OF LUBRICANTS Sampling method is one of the most important factors contributing to effective scheduled oil analysis. To achieve consistent and meaningful data, samples must: Be taken at regular intervals. Be free from external contamination. Be taken at normal operating temperature. Be sampled in the same manner every time. 5.3.1 When to sample? Unless specific information on sampling intervals is supplied in your operating manual or other brochures, use the following guide to determine sampling intervals. 5.3.1.1
Engines:
Consult the operator’s manual for recommended oil change intervals (usually every 250 hours). Sample just prior to draining the oil. 5.3.1.2 Transmissions, Differentials, Final Drives and Hydraulics: Initially sample at 250 hour intervals and just prior to an oil change as indicated by the operator’s manual. If the results indicate no abnormalities after 1000 hours of equipment usage, the intervals may be extended to every 500 hours. 5.3.2 Where to sample? Always draw the sample from the same point in the compartment. 5.3.2.1 Engines: Draw sample from dipstick retaining tube. 5.3.2.2
Transmissions, Differentials, Drives and Planetries:
Final
Draw sample through oil level point or dipstick retaining tube, whichever is provided. 5.3.2.3
Hydraulics:
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Draw sample from the ‘oil fill’ port of the system reservoir, ensuring the sample is taken from the mid-level of the reservoir. 5.3.3 What Technique?
is
an
Effective
Sampling
Ensure all compartments to be sampled are at normal operating temperature. Oil must be well circulated when sampled (within 15 minutes of shutdown) To avoid external contamination, clean all lubricant access areas prior to sampling. Complete the sample description sheet prior to drawing the sample. (Use the guide)
normal distribution of data.A normal distribution of data means that most of the examples in a set of data are close to the "average or mean" while relatively few results head to the outer extremes.We are looking at the data set for an Excavator Pump drive and the information we are doing the study is on Iron (Fe). We need to look at the typical data that we have extracted from the Oil Analysis. Like most data, the outcome from the results will turn out being normally distributed. That means that the Iron analysis will be close to the “mean” while less Iron results will be lower or higher than the “mean”.
Section 6 - Interpretation Tools
6.1
Normalisation
Establishing Testing BenchmarksIntervals need to be specified to compare “apples with apples” across the useful life of the equipment. Oilcheck uses 200 hours or 10,000 Kilometres as a standard on engines and 500 hours or 25,000 Kilometres on all other compartments.The results of each oil analysis are weighted proportionately to fit into the specified category to achieve a “normalised” set of data as shown in the table. Hrs on oil
Results (raw) for IRON
235
91 ppm
216
82 ppm
182
93 ppm
Formulae for normalisation (91 ppm x 200 hrs) 235 hrs (82 ppm x 200 hrs) 216 hrs (93 ppm x 200 hrs) 182 hrs
Normalised result for IRON 77 ppm 75 ppm 102 ppm
The corresponding graph compares “raw” and “normalised” data. The “normalised” data is then compared with the standard deviations to determine the status of the oil.
The x-axis (the horizontal one) is the value in question... Iron, Copper or even viscosity of the oils, for example. And the y-axis (the vertical one) is the number of data points for each value on the x-axis... in other words, the number of EX1800 pump drives that generate x amount of Iron.Now, not all sets of data will have graphs that look this perfect. Some will have relatively flat curves others will be steep. Sometimes the mean will lean a little bit to one side or the other. However, all normally distributed data will have something like this same "bell curve" shape.The standard deviation is a statistic that tells you how tightly all the various examples are clustered around the mean in a set of data. If you can imagine the centre of this target being the mean then all the shots taken around the centre are spread out in proportional groups 68% ended up in the middle 27% just out of centre and 1%on the extreme. When the examples are tightly bunched together and the bell-shaped curve is steep, the standard deviation is small. When the examples are spread apart and the bell curve is relatively flat, that tells you, you have a relatively large standard deviation.
6.2.
Standard Deviation
The standard deviation is kind of the "mean of the mean," and often can help you find the story behind the data. To assist in this we use the term
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Element IRON CHROMIUM LEAD COPPER ALUMINIUM SILICON SODIUM
Mean 160.6 2.7 29.2 4.2 6.7 26 7.2
St dev 113.3 1.2 27.1 3.1 4.2 13.4 4.2
0.5 SD 217.2 3.3 42.7 5.7 8.8 32.7 9.4
1 SD 273.9 3.9 56.3 7.3 10.9 39.4 11.5
2 SD 387.2 5.1 83.4 10.4 15.1 52.8 15.7
3 SD 500.5 6.2 110.5 13.6 19.3 66.2 19.9
68% 27% One standard deviation away from the mean in either direction on the horizontal axis (the red area on the graph) accounts for somewhere around 68 percent of Iron results in this group.
4%
Two standard deviations away from the mean (the red and green areas) account for roughly 95 percent of Iron results. Three Standard Deviations (the red, green and blue areas) account for about 99 percent Iron results.If this curve were flatter and more spread out, the Standard Deviation would have to be larger in order to account for those 68 percent or so Iron results. So that's why the Standard Deviation can tell you how spread out the results are in a set from the meanThe computer will calculate the mean and three levels of Standard Deviation as shown in the table. The analysis results are compared with the Standard Deviation benchmarks to determine the condition of the oil.The recommendations such as 1xSD, 2xSD, 3xSD 4xSD are valid in some instances, yet in others a tighter or looser spread of SD may be selected. For simplicity here, look at the following: 1. If the results are less than 1 Standard Deviation, the outcome is analysed as being “Satisfactory”. For example, having an Iron result less than 273.9. 2. If the results are between 1 and 2 Standard Deviations, the result is assessed as being “Slightly Elevated”. For example, having an Iron score between 273.9 and 387.2. 3. If the oil has a value exceeding 2 but less than 3 Standard Deviations it is assessed as “Elevated”. 4. A value greater than 3 Standard Deviations is assessed as “High”, with values greater than 4 Standard deviations (not shown) would be approaching Critical stage..
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