EPRI_Lubrication Guide 1003085

Lubrication Guide

Revision 3 (Formerly NP-4916-R2)

Technical Report

LI

CE

NS E D

M A TE

RI

AL

Equipment

Reliability

Plant

Maintenance

SupportReduced

Cost

WARNING:Please read the License Agreementon the back cover before removingthe Wrapping Material.

EPRI Project ManagerM. Pugh

EPRI 3412 Hillview Avenue, Palo Alto, California 94304 PO Box 10412, Palo Alto, California 94303 USA800.313.3774 650.855.2121 [email protected] www.epri.com

Lubrication GuideRevision 3 (Formerly NP-4916-R2)1003085

Final Report, October 2001

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIESTHIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS ANACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCHINSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THEORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I)WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, ORSIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESSFOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON ORINTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUALPROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'SCIRCUMSTANCE; OR

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ORGANIZATION(S) THAT PREPARED THIS DOCUMENTBolt & Associates

ORDERING INFORMATIONRequests for copies of this report should be directed to EPRI Customer Fulfillment, 1355 Willow Way,Suite 278, Concord, CA 94520, (800) 313-3774, press 2.Electric Power Research Institute and EPRI are registered service marks of the Electric PowerResearch Institute, Inc. EPRI. ELECTRIFY THE WORLD is a service mark of the Electric PowerResearch Institute, Inc.

Copyright 2001 Electric Power Research Institute, Inc. All rights reserved.

iii

CITATIONS

This report was prepared by

Nuclear Maintenance Applications Center (NMAC)EPRI1300 W.T. Harris BoulevardCharlotte, NC 28262

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Lubrication Guide: Revision 3 (Formerly NP-4916-R2), EPRI, Palo Alto, CA: 2001. 1003085.

vREPORT SUMMARY

A large number of lubricants are used in power plants for various purposes. Maintenancepersonnel need concise guidelines for selecting the correct lubricant for a specific application.Also, specific knowledge is required regarding a lubricants characteristics to determine itsapplicability.

BackgroundThis lubrication guide has traditionally provided useful information to power plant personnelinvolved in this area of plant operation and maintenance. This revision of the Lubrication Guideincorporates changes within the lubrication industry including consolidation and discontinuationof product lines and features. As in Revision 2, it also includes topics that were covered underEPRI report, Radiation Effects on Lubricants, NP-4735.

Objectives To provide general guidance to plant personnel involved with lubricants To provide information on current oils and greases and their operating limitations for

different plant applications

ResultsThis guide addresses lubricants, lubrication, testing, and friction and wear. It includes sectionson basic lubrication, application problems, tests and analysis. Tables are provided that profileeach use category, listed lubricants for specific applications, and temperature and radiationtolerances of these lubricants. A glossary of technical terms is also included. Guidance onselecting the correct lubricant for a specific application is also provided. Information ondetermining the remaining life of a lubricant is addressed, which can help reduce unnecessaryand costly lubricant change-outs.

EPRI PerspectiveKnowledge of lubrication is important to maintenance personnel in their day-to-day work. Thisguide provides, in a concise form, a substantial amount of information on properties ofcommonly used lubricants. Selection of correct and compatible lubricants can help preventunscheduled maintenance or shutdown. Information contained in this guide can be useful to atraining instructor and to persons being initiated in the technology of lubrication. This revisionto the NMAC Lubrication Guide attempts to incorporate recent changes within the lubricationindustry including consolidation and discontinuation of product lines and features.

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KeywordsPlant engineeringPlant maintenancePlant operationsLubricantsLubrication

EPRI Licensed Material

vii

ACKNOWLEDGMENTS

This publication was developed by the Nuclear Maintenance Application Center (NMAC). Thefirst versions of the Guide were prepared by Dr. Bob Bolt and the late Jim Carroll. This thirdversion, built on the prior work, was prepared largely by Dr. Bolt with the major assistance ofDr. Howard Adams. Additionally, Dr. Bolt would like to acknowledge the valuablecontributions from the following:

Chesley Brown TXUJim Fitch NoriaDoug Godfrey Wear Analysis; Bolt & AssociatesBill Herguth Herguth LaboratoriesSteve Mitchell AEP


ix

ABSTRACT

This Guide gives information on lubricants from many manufacturers, suitable for variousnuclear power plant applications. Lubricant operating limits with respect to temperature andradiation dose are listed. The Guide also addresses the basics of how lubricants work, howradiation affects them, and how this relates to their composition. Friction and wear is anotherbasic topic presented, along with lubricant stress effects, shelf life, compatibility, troubleshootingand testing, all important in maintenance. The testing section has received particular attentionwith the addition of several new test methods. A summary of the lubricants study in theEPRI/Utilities Motor-Operated Valve Performance Prediction Program is also included, as it wasin Revision 2. The Guide is intended for use by power plant maintenance and engineeringpersonnel.


xi

CONTENTS

1 LUBRICANTS: WHAT THEY ARE AND HOW THEY WORK ............................................. 1-11.1 Base Oils................................................................................................................... 1-11.2 Key Measurements ................................................................................................... 1-21.3 Additives ................................................................................................................... 1-3

1.3.1 Vl Improvers ......................................................................................................... 1-41.3.2 Detergent/Dispersants.......................................................................................... 1-41.3.3 Basic Metal Compounds....................................................................................... 1-41.3.4 Antiwear and Antiscuff (EP) Additives................................................................... 1-41.3.5 Antioxidants.......................................................................................................... 1-51.3.6 Rust Inhibitors and Antifoamants .......................................................................... 1-61.3.7 Gelling Agents ...................................................................................................... 1-6

1.4 Synthetic Lubricants.................................................................................................. 1-6

2 RADIATION EFFECTS ON LUBRICANTS.......................................................................... 2-12.1 Effect on Elastomers ................................................................................................. 2-8

3 LUBRICATION, FRICTION, AND WEAR ............................................................................ 3-13.1 Hydrodynamic Lubrication (HDL)............................................................................... 3-13.2 Elastohydrodynamic Lubrication (EHL) ..................................................................... 3-23.3 Boundary Lubrication (BL)......................................................................................... 3-3

3.3.1 Physically Adsorbed Film...................................................................................... 3-33.3.2 Chemisorbed Film ................................................................................................ 3-43.3.3 Chemical Reaction Film........................................................................................ 3-5

3.4 Solid Lubricants......................................................................................................... 3-53.5 Nature of Machined Surfaces.................................................................................... 3-63.6 Wear ......................................................................................................................... 3-6


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4 APPLICATION PROBLEMS................................................................................................ 4-14.1 Compatibility of Mixed Products ................................................................................ 4-1

4.1.1 Oils ....................................................................................................................... 4-14.1.2 Greases................................................................................................................ 4-1

4.2 Shelf Life ................................................................................................................... 4-44.3 Time/Temperature/Radiation Considerations ............................................................ 4-54.4 Continuous Versus Intermittent Use and Lube Performance..................................... 4-7

5 TESTS AND ANALYSES .................................................................................................... 5-15.1 Sampling ................................................................................................................... 5-15.2 Troubleshooting ........................................................................................................ 5-15.3 Lubricant Testing....................................................................................................... 5-2

5.3.1 Sensory Tests ...................................................................................................... 5-25.3.2 Other Simple Tests............................................................................................... 5-45.3.3 Diagnostic Laboratory Tests ................................................................................. 5-55.3.4 Standard Laboratory Tests ................................................................................. 5-125.3.5 Analytical Test Methods...................................................................................... 5-14

5.4 Using Test Results .................................................................................................. 5-195.5 Trending.................................................................................................................. 5-195.6 Warning Limits ........................................................................................................ 5-205.7 Cleanup Considerations .......................................................................................... 5-22

6 LUBRICATING MOTORIZED VALVE ACTUATORS .......................................................... 6-16.1 Stem Nut Friction and Wear Off-the-Shelf Products ............................................... 6-26.2 Stem Nut Friction & Wear Solid Lubricants and Improved Nut CuttingProcedure........................................................................................................................... 6-46.3 Search for Improved Actuator Lubricants .................................................................. 6-66.4 Long-Term Thermal Effects On Greases................................................................... 6-96.5 Conclusions ............................................................................................................ 6-11

A APPENDIX A.......................................................................................................................A-1A.1 Lubricant Property Tables .........................................................................................A-1A.2 Footnotes. ...............................................................................................................A-14

B APPENDIX B ......................................................................................................................B-1B.1 Glossary....................................................................................................................B-1


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LIST OF FIGURES

Figure 1-1 Effect of Antiwear and Antiscuff Additives .............................................................. 1-5Figure 1-2 Hydrocarbon Oxidation Process............................................................................. 1-6Figure 2-1 Dose Levels for Radiation Effects .......................................................................... 2-1Figure 2-2 Interaction of a Gamma Photon with Organic Matter.............................................. 2-2Figure 2-3 Upper Limits of Radiation Doses Resulting in Failure of Various Base Fluids ........ 2-3Figure 2-4 Radiolysis Effects on a Lithium Complex-Gelled, Mineral Oil-Based Grease.......... 2-4Figure 2-5 Relative Oxidation Stability of Irradiated Mineral Oil-Based Steam Turbine

Oils in Turbine Oil Stability Tests (TOST) (ASTM D 943) ................................................. 2-5Figure 2-6 Effect of Temperature and Irradiation on Bearing Life of a Sodium Salt-

Thickened, Mineral Oil-Based Grease ............................................................................. 2-6Figure 2-7 Relative Sensitivity of Common Lubricants and Elastomers to Irradiation .............. 2-8Figure 2-8 Resistance of Elastomers to Irradiation.................................................................. 2-9Figure 3-1 Hydrodynamic Lubrication...................................................................................... 3-2Figure 3-2 Elastohydrodynamic Lubrication ............................................................................ 3-2Figure 3-3 Boundary Lubrication (Fragmented Roughness) .................................................... 3-3Figure 3-4 Representation of Physically Adsorbed FilmNon-Polar Molecules ...................... 3-4Figure 3-5 Physically Adsorbed FilmPolar Molecules .......................................................... 3-4Figure 3-6 Chemisorbed Film .................................................................................................. 3-4Figure 3-7 Effects of Various Parameters on Friction Coefficient............................................. 3-5Figure 3-8 Machined Surface .................................................................................................. 3-6Figure 4-1 Compatibility of Mixtures of Greases With Different Gelling Agents........................ 4-3Figure 4-2 Time/Temperature/Irradiation Interplay Continuous Operation in Air of High

Quality Lubricant Under Stress........................................................................................ 4-6Figure 5-1 Observing the Appearance..................................................................................... 5-3Figure 5-2 Detecting the Odor................................................................................................. 5-3Figure 5-3 Viscosity Gage for Measuring the Viscosity of Oils................................................. 5-4Figure 5-4 Sample Blotter Spot Test ....................................................................................... 5-5Figure 5-5 Wear Particle Size/Concentration and Machine Condition ..................................... 5-8Figure 5-6 Detection of Wear and Other Particles ................................................................... 5-9Figure 5-7 Schematic of TGA Setup...................................................................................... 5-15Figure 5-8 Schematic of DSC Apparatus............................................................................... 5-15Figure 5-9 Ruler (Remaining Useful Life Evaluation Routine) Instrument .......................... 5-16


xiv

Figure 5-10 Example of Three Additives and Voltammeter Response................................... 5-17Figure 5-11 Chromatographs of Fresh and Used Gear Oils .................................................. 5-18Figure 5-12 Sample Plot of Lubricant Properties................................................................... 5-20Figure 6-1 Composite of Friction Coefficient (@10,000 lbs) Versus Number of Strokes.......... 6-4Figure 6-2 Cross-Section of Macrograph of New SMB-O Stem Nut Thread Standard

Machining........................................................................................................................ 6-5Figure 6-3 Pin-On-Disk Machine Schematic (Tribometer) ....................................................... 6-7


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LIST OF TABLES

Table 1-1 Oil and Grease Requirements ................................................................................. 1-1Table 1-2 Common Additives in Various Lubricants ................................................................ 1-3Table 1-3 Synthetic Base Oils and Their Application ............................................................... 1-7Table 1-4 Comparative Properties of PAO Synthetic Base Oil and Various Mineral Base

Oils.................................................................................................................................. 1-8Table 2-1 Effects of Irradiation on Common Oils ..................................................................... 2-7Table 2-2 Effects of Irradiation on Common Greases.............................................................. 2-7Table 2-3 Resistance of Elastomers to Effects of Common Oils and Greases......................... 2-8Table 4-1 Compatibility of Greases ......................................................................................... 4-2Table 4-2 Grease Compatibility Tests ..................................................................................... 4-4Table 5-1 Sequence of Lubricant Testing................................................................................ 5-2Table 5-2 IR Peak Regions of Interest..................................................................................... 5-6Table 5-3 Sources of Metals in Lubricants .............................................................................. 5-8Table 5-4 Wear and Its Causes............................................................................................... 5-9Table 5-5 Range Number Determination............................................................................... 5-11Table 5-6 Key Tests for Lubricants........................................................................................ 5-13Table 5-7 Typical Warning Limits for Certain Lubricant Services........................................... 5-21Table 6-1 Friction and Wear Performance Summary (500 Stroke Stem/Stem Nut

Lubricant Tests with SMB-0)............................................................................................ 6-3Table 6-2 Bleeding Tests on Grade 1 Greases (including effects of gelling agents) ................ 6-6Table 6-3 Pin-on-Disk Tribometer Data for Some Grease Types............................................. 6-8Table 6-4 Grease Consistency Changes in Long-Term Thermal Tests ................................. 6-10Table A-1 Turbine Oils ISO Viscosity Grades 32, 46, 68 ........................................................A-1Table A-2 Engine Oils for Large Diesels.................................................................................A-2Table A-3 Low-Pressure Hydraulic Oil ISO Viscosity Grades 32, 46, 68, 100.........................A-3Table A-4 High-Pressure Hydraulic Oil ISO Viscosity Grades 32, 46, 68, 100........................A-4Table A-5 Compressor Oils ....................................................................................................A-5Table A-6 High Load Extreme Pressure (EP) Gear Lubricants...............................................A-6Table A-7 Open Gear Lubricants............................................................................................A-7Table A-8 Antiseizure Compounds.........................................................................................A-8Table A-9 Limitorque Valve Actuator Lubricants.....................................................................A-9Table A-10 Fire Resistant Hydraulic Fluids ..........................................................................A-10


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Table A-11 General Purpose GreasesGrades 00, 0, 1, 2, 3..............................................A-11Table A-12 Coupling Greases ..............................................................................................A-12Table A-13 Grease Types and Performance ........................................................................A-13Table B-1 Viscosity Equivalents .............................................................................................B-4


1-1

1 LUBRICANTS: WHAT THEY ARE AND HOW THEYWORK

Oils and greases have to meet the several requirements shown in Table 1-1.Table 1-1Oil and Grease Requirements

Properties Oils Greases

Prevent metal/metal contact x x

Act as a hydraulic medium x

Act as a coolant x

Carry away contaminants x

Protect against wear x x

Protect against corrosion x x

Protect against deposits x x

Resist foaming x

Remain in place x

Note that the only function exclusive to greases is the ability to stay in place. This results fromthe semi-solid nature of greases. On the other hand, there are several functions exclusive to oilsthat are derived from their fluid nature.

1.1 Base Oils

To perform the indicated tasks, commercial lubricating oils consist of about 85 to 99+ % baseoil. The remainder consists of additives. Additives are used to enhance the properties of the baseoil or to create a necessary property in it. Base oils are classified as:

Mineral oils

Synthetic oils


Lubricants: What They Are and How They Work

1-2

The principal advantage of synthetic oils is their relatively low viscosity at low temperatures.They also can have somewhat better high temperature performance. However, the cost ofsynthetic-based lubricants is 3-8 times the cost of mineral oil-based products. (For additionaldiscussion on synthetic lubricants, see Section 1.4.)

The term mineral oil, as opposed to synthetic oil, implies that little processing is involved inthe manufacture of mineral base oils. This is not true. The fraction distilled from selectedpetroleum crude oils for subsequent base oil manufacture contains many organic molecularspecies. Several of these must be removed to yield a high quality final base oil. Aromatic andwax compounds are two classes that are removed. Aromatics (alternating carbon-to-carbondouble bonds in six membered rings) show a particularly high rate of viscosity change withtemperature. This is not a good property in a lubricant. Waxes are solids at room temperature andare, therefore, unsuitable in base oils. Removing these requires considerable processing. Physicaltreatment, for example solvent refining, is still used as a method of removal, but catalytichydrogenation under pressure and temperature is now the preferred method of removal.

The product of solvent refining of a base oil feed is called a Group I base oil. Relatively mildcatalytic hydrogenation yields a Group II base oil, while more rigorous hydrogenation produces aGroup III base material. Some properties of these and of a common synthetic hydrocarbon baseoil (Group IV) are listed in Table 1-4.

1.2 Key Measurements

Viscosity is a measure of a fluid's resistance to flow, in other words, its fluidity. It is measured incentistokes (cSt.). The viscosity at 40C is used in industrial oil grading. For example, a 32 gradehas a viscosity at 40C of around 32 cSt. Other grading methods exist but they are used primarilyfor engine oils. Some of these, including their interrelationships, are shown in the Glossary(Appendix B).

Viscosity Index (VI) is a measure of viscosity change with temperature. VI has its origins inpetroleum antiquity. An oil derived from a Gulf Coast crude oil showed a high rate of change ofviscosity with temperature and was arbitrarily given a VI value of 0. A Pennsylvania crude-derived oil, with a low rate of change of viscosity with temperature, was given a VI of 100. Alloils since then have been compared on this scale. The best of the normal mineral base oils(Group I and some Group IIs) have VIs in the 90's. Synthetic oils and some very highly refinedmineral oils (Group III, some Group IIs) can have VIs in the 105 to 160 range, reflecting theirsuperior viscosity/temperature properties.

Temperature Viscosity Coefficient ()))) is a more fundamental indication of change of viscositywith temperature, which may soon become more widely used. It is (see Table 1-4 for somevalues):

= viscosity in cSt at 40C viscosity in cSt at 100C viscosity in cSt at 40C

Grease consistency is measured by penetration values. These are determined from thedistance (in 0.1 mm units) that a standard American Society for Testing and Materials (ASTM)



1-3

cone sinks into a standard cup of grease at 77F (25C). Because consistency can change withshear or working, greases are often worked in a standard worker before penetrations aremeasured. The worked penetrations corresponding to the various grease grades are shown in theGlossary (Appendix B). P60 refers to the penetration after 60 double strokes in the worker; P 10,000refers to 10,000 double strokes, and so on. Grease grades are determined by P 60 values (seeAppendix B for grade determinations).

Dropping Point is another ASTM grease measurement. It is the temperature at which a greasejust begins to melt or separate. The use temperature of a product is related to its dropping point.

1.3 Additives

Up to about 15% of a finished lubricant consists of materials added to the starting base oil tocreate properties or enhance those that already exist. Table 1-2 shows finished lubricants and theadditives they might contain.

Table 1-2Common Additives in Various Lubricants

Common Lubricants Engine Oils TurbineOils

Hydr.Oils

GearOils

Compr.Oils

Greases

Gasoline Diesel

Additives

VI Improvers x x x x

Detergent/Dispersants x x x

Basic MetalCompounds

x x x

Antiwear Agents x x x x x x

Antiscuff (EP) Agents x x*Antioxidants x x x x x x x

Rust Inhibitors x x x x x x x

Antifoamants x x x x x x

Gelling Agents x

* Premium greases for ball and roller bearing lubrication generally do not contain antiscuff agents.



1-4

1.3.1 Vl Improvers

Viscosity Index (VI) improvers are listed first because they are used in the largest amounts toperform their function. They thicken lower viscosity base oils and, in the process, flatten themixture's viscosity/temperature slope. This improves VI. These additives are widely used tomake mineral oil-based multigrade engine oils. VI improvers are not required to makemultigrade products from synthetic base oils or some Group III mineral base oils. This is becauseof the superior viscosity/temperature properties of such base oils (see Table 1-4).

1.3.2 Detergent/Dispersants

Detergent/dispersants keep any deposit precursors in suspension instead of agglomerating to plugpiston rings, key oil passages, etc. or collecting as sludge. Detergent/dispersants were among thefirst additives used and continue to be of high importance in engine oils where deposits can comefrom combustion products. They are sometimes used in compressor oils, as well.

1.3.3 Basic Metal Compounds

Basic metal compounds have some detergency and good rust preventing properties but theirmain function is to neutralize acids in diesel engine oils. The acids come from the combustion ofsulfur in fuel and the fixation of nitrogen in combustion air. Reaction with water converts thesulfur and nitrogen oxides to corresponding acids. If not neutralized, they cause corrosive wearof engine parts. The need for basic metal compounds (base reserve, high base number) in partdepends on the sulfur content of the fuel the lower the sulfur the less need for base. Thenational trend toward low sulfur diesel fuel to control emissions will eventually reduce the use ofbasic metal compounds.

1.3.4 Antiwear and Antiscuff (EP1) AdditivesAntiwear additives are very widely used in engine and industrial lubricants, but not universallyso. Antioxidants, on the other hand, are universally used. Antiscuff additives are less widelyused, as indicated in Table 1-2. Antiscuff materials can be viewed as more surface-invasive and,therefore, stronger in action than antiwear additives. Both antiwear and antiscuff additivesfunction by interposing a relatively shear-resistant chemical film between load bearing metalsurfaces. The general mechanism by which these additives work is shown in Figure l-l 2.

At the top, two moving metal surfaces under little or no load are held apart by an oil film. Withthe application of a load, metal-to-metal contact occurs. At the bottom, when the load is applied,the contact is prevented by a tough chemical film. Sulfur/phosphorus compounds are the mostcommon antiwear agents and they form films of iron, sulfur, and phosphorus compounds toprotect the surfaces. Active, organic sulfur compounds are the principal materials used as

1 Antiscuff is a modern replacement for the term, EP. Scuffing is defined as metal transfer due to adhesion

in metal-to-metal contact.2 Footnote refers to q, Appendix A, Section A.2.



1-5

antiscuff agents. All of these additives act similarly in both oils and greases and they can betemperature-sensitive. Mild antiwear can also be provided in greases from the gelling agents.

Figure 1-13Effect of Antiwear and Antiscuff Additives

1.3.5 Antioxidants

The principal enemy of any lubricant is oxidation. The onset of oxidation cannot be preventedbut only delayed. The delay is called the induction period. Antioxidants extend the inductionperiod very effectively. Once this period is exceeded, however, oxidation can occurexponentially, as shown in Figure 1-2. This results in physical and chemical property changes,for example, fluidity change and acid formation. In common with all chemical reactions,oxidation increases with temperature the rate doubles with each increase of about 18F (10C).However, doubling a very low rate still yields a low rate and the rate is low during the inductionperiod.

3 Footnote refers to q, Appendix A, Section A.2.



1-6

Figure 1-2Hydrocarbon Oxidation Process

1.3.6 Rust Inhibitors and Antifoamants

Rust or corrosion inhibitors are also widely used. They perform by forming a weakly adsorbedfilm on the surfaces to be protected. An antifoamant is also used in most oils. They are polymersand silicone fluids in low concentration, which affect surface tension to reduce the foamingtendency. They also help provide good deaeration properties. Recently, there is a move awayfrom silicone antifoam materials for oils, for example, turbine oils. This is because there can betight silicon content specifications to control dirt contamination.

1.3.7 Gelling Agents

A gelling agent is used to convert an oil into a grease, thus providing the lubricant with itsunique stay-in-place function. The oil that is gelled also contains the other additives requiredto provide the necessary properties shown in Table 1-2. In addition, the gelling agentidentity defines many of the grease's other performance characteristics. These are detailedin Appendix A, Table A-13.

1.4 Synthetic Lubricants

Synthetic lubricants are man-made lubricants whose base oils are chemical productsmanufactured or synthesized to provide properties not available in Group I and some Group IImineral-oil-based products. Although the synthetics represent less than one percent of the totallubricant inventory, they are available for and are used in many applications. Table 1-3 showsthe various classes of synthetic base oils and the finished products in which they are used.



1-7

Table 1-3Synthetic Base Oils1 and Their Application

Engine Oils IndustrialOils

Greases FireResistant

Oils

RelativeCost2

Jet Other

Synthetic Oils

Poly(alpha-olefins)(PAOs)

x x3 x3 4-8

Diesters x x4 5-7

Polyolesters x 10-14

Phosphate Esters x5 10

Polyethers(Polyglycols)

x 6-8

Silicones(Siloxanes)7

x6 x6 30-100

Perfluoropolyethers x x 80-800

Polyphenylethers x x 100+

Chlorofluorocarbons x 100+

1 In the field of metalworking/cutting fluids, water-based fluids are sometimes called synthetic.

2 Approximate cost multiplier relative to most common mineral oil.

3 Mobil SHC series, Mobilgrease 28.

4 Beacon 325 (Exxon).

5 Fyrquel (Akzonobel), etc.

6 Dow Corning; GE.

7 Including halogenated species.

The poly(alpha-olefins) (PAOs - Group IV) are the most widely used synthetic base oils inindustrial and automotive lubricants. However, the differences between them and the new highlyrefined (hydrocracked4) mineral oil base stocks (Group III) are becoming blurred as shown inTable 1-4. Because of this, the marketplace is likely to see fewer PAO-based products in thefuture. The hydrocracked base oils cost half as much as the PAOs and their properties are oftensimilar.

4 This process involves hydrogenation of normal mineral oil feed material with special catalysts. These catalysts

direct the process to rearrange the undesirable molecular constituents of the feed into species that resemble those inthe polymerization of the alpha-olefins (PAOs). The severity of the process dictates the properties of the finalproduct as in Table 1-4.



1-8

Table 1-4Comparative Properties of PAO Synthetic Base Oil and Various Mineral Base Oils

Mineral OilsGroup I*

Mineral OilsGroup II*

Mineral OilsGroup III*

PAOAPI Group IV*

Viscosity, 40C, cSt 32 44 39 32

Viscosity, 100C, cSt 5.3 6.6 7.0 6.0

Viscosity Index 95 102 135 136

Pour Point, C -15 -15 -20 -66

Flash Point, C 210 230 240 246

Fire Point, C 240 272

Evaporation Loss,Wt%(6.5 Hr. at 204C)

16 4

Aniline Point, C(ASTM D 611)

108 115 127 127

* American Petroleum Institute (API) base stock classification

The good low temperature properties of the PAOs are reflected in the viscosities, viscosity index,and pour point. They are matched, except for the last, by the Group III mineral base oil. Thelower volatility for a given viscosity shows up in higher fire point and lower evaporation loss.The aniline point is a measure of solvency the lower the number, the higher the solvency. Herethe PAO and Group II and III oils are inferior to the normal, or Group I, mineral oil. That is, ifsludge is formed, it will precipitate out later with a Group I-based product. However, the sludge,which is oxidized material, might not form so readily with the synthetic oil- or Group II- or III-based product. This is because the Group II, III, and IV oils generally give a higher degree ofoxidation resistance with a given amount of antioxidant.

Improved performance with synthetic oil-based lubricants comes with an increased price tag.This is shown in Table 1-3. Such costs make it hard to justify the use of synthetic-based productsunless the application demands their superior properties. For example, if equipment needinglubrication is used in subzero weather, it is worth the added cost reliably to start or operate thefrigid apparatus with a PAO-based oil. The cost, of course, is only half as much if a Group III-based product can be used. In another example, if fire-resistant oil is needed, then the additionalcost is justified. But if these properties are not required, there is no need to use expensivesynthetic products. The vast majority of the nuclear power plant lubrication requirements can bemet with high quality mineral oil-based products.


2-1

2 RADIATION EFFECTS ON LUBRICANTS5

In normal operation, lubricants must withstand the stresses of temperature, shear, pressure (load),and exposure to oxygen in the air. In nuclear power plants, exposure to nuclear radiation is anadded stress. Overall effects of thermal and radiation exposures are similar. For example, bothshow thresholds below which changes in bulk properties of exposed materials are not significant.Both also accelerate oxidation, the main foe of lubricants in service.

With radiolysis, as well as pyrolysis, color change occurs first, signaling beginning oxidation andother structural changes. Gas evolution also takes place early, followed by changes in fluidity assecondary reactions take over. The final product of very high thermal or radiation exposure is anintractable solid, no longer a lubricant.

Radiation effects are directly related to the radiation energy input. This input is expressed interms of the rad (100 ergs/gram of absorber = 4.3 X 10-6 Btu/lb). The radiation sensitivity oflubricants versus other things is shown in Figure 2-1. The more complex the irradiated object theless tolerant it is of irradiation. Note the effect on the ultimate in complexity homo sapiens!

Figure 2-1Dose Levels for Radiation Effects

5 Bolt, Carroll, Radiation Effects on Organic Materials, chapter 9, Academic Press (1963); Bolt chapter in Boozer,

Handbook of Lubrication, Volume 1, CRC Press (1983).


Radiation Effects on Lubricants

2-2

Mechanistically, incident gamma radiation affects organic matter through initial collisions withelectrons of individual atoms of molecules. This is shown in Figure 2-2. About half an incomingray's energy is given up to a scattered electron and the weakened gamma ray goes on to repeatthe process. The charged electron, knocked from its position by the incoming gamma ray, goeson to lose its added energy by creating increasingly intense ionizations and excitations inneighboring molecules.

Figure 2-2Interaction of a Gamma Photon with Organic Matter

Incident high energy neutrons interact initially with atomic nuclei of irradiated material insteadof with the electrons in gamma ray interactions. This knocks out protons and these chargedparticles go on to act in the same fashion as described for incident gamma rays.

Primary interactions in radiolysis take place in some 10-14 seconds. Secondary reactions thatresult in new molecular products occur in the next 10-2 seconds. To minimize change, excitationwithout decomposition needs to be fostered. Use of additives, for example selected compoundscontaining sulphur that neutralize excitation without C-C bond fissure, is a means of doing this.Another means is to employ base oil molecules that dissipate the input energy largely throughthe generation of heat (resonance), that is, aromatic compounds. Thus, the effect on lubricantsdepends on the chemical makeup of both the base oil and additives. Figure 2-3 shows this forbase oils.



2-3

Figure 2-3Upper Limits of Radiation Doses Resulting in Failure of Various Base Fluids

Note the effect of aromatic content the polyphenyls, poly(phenyl ethers), and alkylaromaticshead the list in radiation resistance. Phenyl groups are basic units of aromaticity. Aromatics,because of their poor viscosity/temperature properties, are deliberately removed from mineralbase oils. However, aromatic compounds can be designed through synthesis to have goodproperties. Such materials (alkylaromatics) are employed in making lubricants designed formaximum radiation resistance. The introduction of phenyl groups even into poor performingmolecules will improve their radiation resistance. For example, phenyl silicones are a notchbetter than methyl silicones in radiation resistance.

The physical effect of radiolysis on greases is that they mostly soften with initial exposure,reflecting degradation of their sensitive gel structure. Eventually, this is followed by hardeningas the effect on the oil component takes over. Figure 2-4 shows the typical softening effect.Although this grease exhibits stability in the 106-108 rad region, other greases can either harden orsoften in this region. This is before the major softening indicated in Figure 2-4 and before effectson the oil component set in.



2-4

Figure 2-4Radiolysis Effects on a Lithium Complex-Gelled, Mineral Oil-Based Grease

The effect of radiation exposure on oxidation stability, a key property of turbine oils, is shown inFigure 2-5. Other effects on oils include gas evolution, evidenced by a decrease in flash pointand increase in vapor pressure. The gas is hydrogen and low molecular weight hydrocarbons thatcome from C-H and C-C bond fissure. The C-C bond breakage can also yield compounds thateventually double or similarly polymerize to cause viscosity increase.



2-5

Figure 2-5Relative Oxidation Stability of Irradiated Mineral Oil-Based Steam Turbine Oils in TurbineOil Stability Tests (TOST) (ASTM D 943)

The effect of radiation dose rate is also highlighted in Figure 2-5. The doses shown weredelivered to the test samples at widely different rates differing by a factor of about onethousand. Yet the variation in the test results falls within the reproducibility limits of the ASTMD 9436 test. Thus, there appears to be no appreciable dose rate effect. All the exposures weremade in air for the indicated doses and then the oils were tested. Note that the dose below whichno significant oxidation takes place is about 5 X 106 rads.

This dose rate concern comes up primarily in applying radiation effects studies to plantsituations. Most radiation effects studies are accelerated, that is, at higher dose rates than those inthe plant, to allow results in a reasonable time. The answer is complicated by oxidation effects more oxidation would be expected over the longer term, simply due to heating in air underirradiation. Oxidation is mitigated by oxidation inhibitors. All high quality lubricants have suchantioxidants. Without them oxidation could be interpreted as a dose rate effect.

Even with good inhibitors, the acceleration of oxidation in the presence of radiation is animportant consideration from a maintenance point of view. Lubricant life will be reduced if thereis excessive exposure to oxygen in the air, for example, where there are unrepaired air leaks onthe inlet side of a pump in a radioactive area. In the example, a rich supply of oxygen andirradiation at high temperature can take its toll on the lubricant.

6 ASTM D 943-81 (91), Test Method for Oxidation Characteristics of Inhibited Mineral Oils [Turbine Oil

Stability Test (TOST)].



2-6

Generally, radiolysis of lubricants is not a problem in nuclear power plants. It takes radiationdoses above those prevailing in normal nuclear plant operations to make appreciable changes inbulk properties of lubricants. An accident scenario (a DBA) may produce high enough radiationexposure to cause significant property changes. In such a case, the equipment being lubricateddoesn't have to operate very long or be maintained. The equipment itself is very tolerant offluidity changes in lubricants. For example, antifriction bearings in motors can go just fine, atleast in the short run, with grease worked penetrations from about 200 to over 400. This isequivalent to a change in consistency from a 4- to a 00-grade a wide variation.

This tolerance exists even under stress. Figure 2-6 shows test data for a grease in a 10,000 rpmbearing at various temperatures. An Arrhenius plot (log bearing life versus inverse of absolutetemperature) is shown. Note the change in life of irradiated grease versus that of unirradiatedproduct. It took over 108 rads to make much of a difference in the grease's performance.

Note: Irradiations were conducted in air (allowing some oxidation) to the doses shown.Tests as per ASTM D 33367 were then run on the greases.

Figure 2-6Effect of Temperature and Irradiation on Bearing Life of a Sodium Salt-Thickened, MineralOil-Based Grease

7 ASTM D 3336, Test Method for Life of Lubricating Greases in Ball Bearings at Elevated Temperatures.



2-7

The effects of irradiation on oils and greases are summarized in Tables 2-1 and 2-2.Table 2-1Effects of Irradiation on Common Oils

Radiation Dose Effect

< 106 Rads No unusual problems.

106 - 107 Rads Things begin to happen; someturbine oils borderline.

107 - 108 Rads Most oils usable; somemarginal.

108 - 109 Rads The best oils usable; mostbecome unusable.

109 - 1010 Only special products willwork.

> 1010 No oil usable.

Table 2-2Effects of Irradiation on Common Greases

Radiation Dose Effect

< 106 Rads No unusual problems.

106 - 107 Rads Things begin to happen; some greases borderline.

107 - 108 Rads Most high quality products usable; others not.

108 - 109 Rads Most greases unusable.

109 - 5 x 109 Rads Special products required.

> 5 x 109 Rads No grease usable.

Values for temperature and radiation operating ranges are given for individual products inAppendix A, Tables A1-A12. In these tables, the first number listed in each category is the valuebelow which little, if any, property change will occur and long use life can be expected. Thesecond number is the point where appreciable change is expected and surveillance of theequipment is required. The need for lubricant changeout should be anticipated at this point.



2-8

2.1 Effect on Elastomers

Elastomers are used frequently as seal materials in nuclear power plants. If one is concerned withradiation-resistance, elastomers are the weak link. Figure 2-7 shows the resistance to irradiationof elastomers versus lubricants. The elastomers are about ten times more sensitive to radiationthan lubricants.

Figure 2-7Relative Sensitivity of Common Lubricants and Elastomers to Irradiation

Table 2-3 shows the effect of common lubricants on various elastomers. Neoprene and Nitrilerubber and the epichlorohydrins are the principal oil and grease resistant products.

Table 2-3Resistance of Elastomers to Effects of Common Oils and Greases

Elastomer ResistanceNatural Rubber Very PoorNeoprene Good - ExcellentEthylene/propylene Very PoorIsoprene Very PoorNitrile (high) ExcellentEpichlorohydrin ExcellentUrethane Fair - ExcellentSilicone Fair - Poor



2-9

The picture changes somewhat as the elastomers are exposed to radiation. Figure 2-8 illustratesthis performance. The natural rubbers and urethanes are most resistant to radiation, with thenitriles ranked a close second.

Figure 2-8Resistance of Elastomers to Irradiation


3-1

3 LUBRICATION, FRICTION, AND WEAR

Three lubrication mechanisms have been established in tribology the study of surfaces inrelative motion. These are:

Hydrodynamic lubrication (HDL) Elastohydrodynamic lubrication (EHL) Boundary lubrication (BL)

A single mechanism might not prevail in any one application but a combination might existdepending on geometry and/or operating conditions. For example, the balls in ball bearingsinvolve EHL in their relationship to the bearing races and BL in their relationship to the cages orretainers. It is important to understand the three types of lubrication in order to be clear aboutlubricants and how they function.

Friction is the resistance to the relative motion of surfaces and is an indicator of the efficiency ofthis motion. It is important because poor efficiency relates to high energy consumption. Wear, orthe undesirable removal of material from contacting surfaces due to relative motion, shortensequipment life and decreases its reliability.

3.1 Hydrodynamic Lubrication (HDL)HDL conditions exist when a fluid film completely separates moving surfaces and there is nosurface-to-surface contact. This is the most desirable regime of lubrication because friction andwear are low under these conditions. HDL is the most common mode of lubrication forcomponents of industrial machines. Examples include simple journal bearings and bushings, andturbine shaft bearings. Factors affecting HDL are the viscosity of the lubricating fluid, itsadhesion to the surfaces, the sliding or rolling velocity of the components, the shape of thesurfaces, and pressure (load) between them.

Film thicknesses for effective HDL range from 0.0001 to 0.005 inches (40-200 microns). Thecreation of such films is fostered when the shape of the surfaces allows a wedge of lubricant toform between them (see Figure 3-1). The failure of HDL usually results from too thin a film, dueto high temperatures, that reduces the viscosity of fluids, low speed that discourages wedgeformation, and shock loads. Another very common cause of film failure is damage bycontaminants, such as dirt, in the oil.


Lubrication, Friction, and Wear

3-2

Figure 3-1Hydrodynamic Lubrication

3.2 Elastohydrodynamic Lubrication (EHL)The name, elastohydrodynamic, implies that a full oil film exists between moving surfaces thatare elastically deformed. EHL occurs only in situations where loads are concentrated over smallareas, for example between balls/rollers and races in rolling element bearings and between gearteeth. In EHL the load is sufficient to deform the surfaces elastically at the point or line of nearcontact (Figure 3-2). The oil is trapped between the deformed surfaces and the resulting highpressure increases the oil's viscosity by several orders of magnitude. The surface deformationalso increases the load bearing area. The combination of extremely high oil viscosity andincreased area over which the load is applied keeps the surfaces from touching.

Figure 3-2Elastohydrodynamic Lubrication

Lubricant film thickness in EHL is smaller than in HDL and the thinner the film for a given oilviscosity the higher the friction. As with HDL, conditions that make for thinner films shortencomponent life in EHL. High temperatures and loads, low speed or oscillatory operation, andespecially lubricant contamination, shorten life. If bearings oscillate, HDL and EHL fail to occur.Wear is low under ideal EHL conditions. Failure of components in EHL is by contact fatigue.



3-3

Because of the cyclic elastic deformation, fatigue cracks and pits are formed. This contact fatiguedetermines the catalog life of a rolling element bearing.

3.3 Boundary Lubrication (BL)BL conditions prevail when HDL and EHL fail and surface-to-surface contact occurs (see Figure3-3). The word, boundary, suggests surface involvement. BL occurs with high loads andtemperatures, low sliding velocities, and rough surfaces. Examples of BL are bearings duringstart up and shut down, oscillating bearings, piston rings at top-dead-center, worm gears, andmetal cutting operations. Friction and wear in BL are dependent upon the shape and compositionof the surfaces and the properties of the lubricant. Friction results from the shear of theinterfacial material, which includes adhesion between the surfaces and the shear of other solidsor liquids in the contact. For example, if the additives in an oil form a soap film of low shearstrength on the surface, friction will be low. If the film formed is a shear resistant inorganic salt,for example iron sulfide, friction will be higher. Three types of films might form in BL,physically adsorbed, chemisorbed, and chemical reaction films.

Figure 3-3Boundary Lubrication (Fragmented Roughness)

3.3.1 Physically Adsorbed Film

Physically adsorbed film involves the adsorption of the non-polar molecules of the base oil atrandom on the surfaces (see Figure 3-4). The adsorption is reversible so, as temperatureincreases, the film desorbs and fails to keep the asperities in the surfaces apart (for asperities, seeSection 3.5). Mineral oils or PAO synthetic base oils are in this category. If the oil molecules arepolar, for example a polyester synthetic, their adsorption is stronger because of their closepacked nature (see Figure 3-5). Higher temperatures are required to desorb them.



3-4

Figure 3-4Representation of Physically Adsorbed FilmNon-Polar Molecules

Figure 3-5Physically Adsorbed FilmPolar Molecules

3.3.2 Chemisorbed Film

Chemisorbed films (see Figure 3-6) are chemical reaction products between long chain polarcompounds in the oil (or compounds that are added to it) and compounds in the metal surfaces.An example is the reaction between a fatty acid in the oil and a metal oxide film from the surfaceto form a soap. The reaction is irreversible so an increase in temperature increases its rate. Themelting point of the soap film is the temperature limitation. The additives in an oil thatchemisorb are termed lubricity additives because they reduce friction as compared to that of thebase oil alone.

Figure 3-6Chemisorbed Film (Xs indicate chemical bond)



3-5

3.3.3 Chemical Reaction Film

Chemical reaction films are also formed through irreversible reactions but the products areinorganic salts. Additives such as sulfur compounds react with surfaces containing iron to formiron sulfide. Such high melting point compounds inhibit scuffing by preventing bare metal-to-metal contact. They are called antiscuff (formerly known as EP) additives. Oxygen, which is inoils from the air, can also act as an antiscuff agent by reacting with metals to form thicker oxidefilms and prevent metal-to-metal contact.

The relationship between HDL and boundary lubrication (BL) for various operating conditions isshown in Figure 3-7. Note the effects of the various parameters on the friction coefficient. With agiven speed and load, a low viscosity oil will allow boundary lubrication and a very highviscosity oil will increase fluid friction.

Figure 3-7Effects of Various Parameters on Friction Coefficient

3.4 Solid Lubricants

The presence of a film or a coating of other solids between surfaces reduces surface-to-surfacecontact. It might also reduce friction and wear. Solid lubricants are classified as follows:

The metal oxides that form in air, for example iron oxide, Fe3O4, on steel (which reducesfriction), or aluminum oxide (which increases friction).

Preformed coatings such as soft lead or Babbitt on aluminum in a journal bearing, thelaminar graphite or molybdenum disulfide on steel, or poly(tetrafluoroethylene) (Teflon) onsteel.

Boundary lubricant films such as soap from a fatty acid in the oil, or iron phosphate fromtricresyl phosphate additive, iron borate from boron additive compound, or iron sulfide froma sulfur additive compound in the oil.

Inorganic conversion coatings such as iron/manganese phosphate on steel.



3-6

3.5 Nature of Machined Surfaces8

Machined metallic surfaces are rough on a microscopic scale (see Figure 3-8) and covered with athin film of oxide. The microscopic bumps contained on these surfaces are called asperities.When two machined surfaces are placed together, the area of real contact (where a few asperitiestouch) is much less than the apparent area of contact. This real contact area increases with loadbecause more asperities are crushed, thus increasing the contact surface.

Figure 3-8Machined Surface

3.6 Wear

Wear is the undesirable removal of solids from a sliding or rolling component. There are manykinds of wear. In analyzing a wear problem in a machine, it is necessary to determine the kind ofwear that occurred. Analysis requires microscopic examination of the worn area and a close lookat the used lubricant. Wear is generally proportional to the applied load and the amount ofsliding. The major kinds of wear are: Adhesive Wear the removal of material due to adhesion between surfaces.

Mild adhesion is the removal of surface films, such as oxides, at a low rate. This is theminimum wear expected under BL conditions.

Severe adhesion the removal of metal due to tearing, breaking, and melting of metallicjunctions. This leads to scuffing or galling of the surfaces and even seizure.

Abrasive Wear the cutting of furrows on a surface by hard particles, (for example, sandparticles between contact surfaces, or hard asperities on an opposing surface). Hard coatingscan reduce abrasive wear.

Erosive Wear the cutting of furrows on a surface by hard particles contained in a fluidtraveling at high velocity. Wear caused by sand blasting is an example of erosive wear.

Polishing Wear the continuous removal of surface films, laid down via a chemicalreaction from an additive in oil or by very fine hard particles in the lubricant, and so on.

8 Godfrey, Douglas, Recognition and Solution of Some Common Wear Problems Related to Lubricants and

Hydraulic Fluids, Lubrication Engineering, 43, 2 (1987).



3-7

Contact Fatigue the cracking, pitting, and spalling of a surface in sequence due to cyclicstresses in a contact. Contact fatigue is most common in rolling element bearings, gear teeth,and cams.

Corrosive Wear the removal of corrosion products from a surface by motion, such as therubbing off of rust.

Fretting Corrosion the removal of metal oxides from a surface due to a reciprocatingsliding motion of extremely low amplitude generated by vibration.

Electro-Corrosive Wear the removal of metal by dissolution in a corrosive liquid with theaid of electric currents. One source of currents is streaming potential from high velocityfluids. The oil serves as the electrolyte.

Fretting Wear localized wear of lubricated surfaces due to reciprocating sliding ofextremely low amplitude because of vibration.

Electrical Discharge Wear the removal of molten metal from surfaces due to electricalsparks between them. High static voltages are sometimes generated by large rotatingmachinery and these are relieved by sparking to regions of lower potential.

Cavitation Damage the removal of material due to cracking and pitting caused by high-energy implosions of vacuous cavities in a cavitating liquid. Liquids cavitate when suddenlysubjected to low pressures.

False Brinelling localized wear in lubricated rolling element bearings due to slight rockingmotion of rollers against raceways. Wear depressions match the position of the rollingelement.


4-1

4 APPLICATION PROBLEMS

4.1 Compatibility of Mixed Products

Lubricants can be incompatible with one another on mixing and can potentially causedegradation of properties and performance. Solid formation with oil mixtures can take placebecause of additive interaction or solubility difficulties. With greases, the usual result ofincompatibility is breakdown of the grease gel structure to produce softness. Both of theseeffects can be undesirable in lubricant applications.

Incompatibility can be avoided by not mixing products. Procedures should be set up to eliminateunwanted mixing. When a change to a new product is dictated, careful cleanup should beemployed to keep less than about 5% of the old material in the new. Remember, don't mix! Ifyou inadvertently do, you face incompatibility risks.

4.1.1 Oils

Lube oils are mostly compatible and miscible with one another in all proportions. A notableexception is mixing a product that contains a chemically acidic additive, for example a turbineoil, with a product that contains a basic additive, for example an engine oil. One will neutralizethe other in the presence of moisture and frequently cause a precipitate to form. Precipitates canplug filters and/or other oil passages and cause oil starvation and equipment failure. If you don'tknow the chemical makeup of the particular products you have, your lubricant supplier can giveguidance on this point so you can avoid the acid/base concern. (Anyhow, mixing of lubricantsshould be avoided.)

4.1.2 Greases

These products present a different case. With inadvertent mixing, possible additive interactions(other than those involving gelling agents) pose only some loss of those functions provided bythe reactants. Precipitates are generally no problem (grease is already semi-solid). Gelling agentinteraction is a concern, depending on the application. Table 4-1 gives compatibility information(Meyers, E. W., NLGI Spokesman 47, (1), 24,1983; Meade, F.S., Compatibility of Greases,Rock Island Arsenal Report 61-2132, 1961). Examples of data on which the table is based are inFigure 4-1. (See also Note No. 5, NMAC Lube Notes, July 1993.)

A consistency change of 30 points or less in worked penetration in more than one mixture in agiven set denotes compatibility (C) in the table. This change is measured by deviation from thestraight line between the two 100% points. Softening is the most likely result of incompatibility,


Application Problems

4-2

although hardening can take place (< 10% of the cases). Softening is of little concern in acontained system, such as a Limitorque gearbox (unless leakage is rampant). It is only the stay-in-place function that is affected the lubrication function is largely handled by the oilcomponent and its soluble additives. A problem does occur if the grease flows away from thepart being lubricated. Rolling element bearings are vulnerable here although they have quite atolerance for changes in grease consistency. This tolerance runs from about 200 to about 400 inworked penetration. However, the departure from around the 280 norm might cause someincrease in required maintenance.

Table 4-1Compatibility of Greases

Alu

min

um C

om

plex

Bar

ium

So

ap

Calc

ium

Soa

p

Calc

ium

12-

Hydr

oxys

tear

ate

Calc

ium

Co

mpl

ex

Inor

gan

ic (C

lay)

Lith

ium

So

ap

Lith

ium

12

-

Hydr

oxys

tear

ate

Lith

ium

Co

mpl

ex

Poly

ure

a

Sodi

um

So

ap

Calc

ium

Sul

fon

ate

Com

ple

x (C

alci

um

Carb

on

ate/

Sulfo

nat

e

CCS)

Aluminum Complex I I C I I I I C I NA I

Barium Soap I I C I I I I I I NA B

Calcium Soap I I C I C C B C I C NA

Calcium 12-Hydroxystearate

C C C B C C C C I NA NA

Calcium Complex I I I B I I I C C NA C

Inorganic (Clay) I I C C I I I I I B I

Lithium Soap I I C C I I C C I C C

Lithium 12-Hydroxystearate

I I B C I I C C I NA C

Lithium Complex C I C C C I C C I NA C

Polyurea I I I I C I I I I C I

Sodium Soap NA NA C NA NA B C NA NA C I

Calcium SulfonateComplex (CalciumCarbonate/Sulfonate CCS)

I B NA NA C I C C C I I

*Incompatiblity is defined as a change exceeding 30 points (1 point = 0.1mm) in ASTM worked penetration in more than one of25/50/75% blends. B = Borderline Compatibility, C = Compatible , I = Incompatible, NA = Not Available.



4-3

As with oils, different greases should not be mixed. The data cited in the table should beconsidered generic in nature. A C in Table 4-1 is not an endorsement to allow mixing becausedifferent grease formulations might give different data. With inadvertent mixing, compatibilityrisks are generally less if products with at least the same gelling agent are involved. However,reversals do occur. To be sure of compatibility or incompatibility, tests on specific greases mustbe run.

Figure 4-1Compatibility of Mixtures of Greases With Different Gelling Agents

Compatibility test results will sometimes vary with the method used. Table 4-2 lists some ofthese methods. High temperatures in the storage (aging) phase are employed to provide testacceleration and assure that any incompatibility will be picked up. A consideration here is not toexceed the heat stability of the individual mixture components. The more severe mix proceduresare undertaken to assure thorough mixing.

The method we prefer involves 25/75, 50/50, and 75/25 mixtures (10/90 and 9/10 are sometimesalso used) of two components stirred with a hand-held electric mixer before aging at 250F(121C) for 72 hours. The starting materials get the same treatment. Then, after cooling to roomtemperature, the 60-stroke worked penetrations are run on all samples. Compatibility/incompatibility is determined as in Figure 4-1. Dropping points can also be run on the treatedsamples. ASTM has now developed the compatibility test listed in Table 4-2. It is more complexand, therefore, three times as expensive to run as the method just cited. Its interpretation is alsomuch more restrictive.



4-4

Table 4-2Grease Compatibility Tests

Group Mix Storage(Aging) Time

Temp Difference in P60 1 to Fail

Rock IslandArsenal

Hand Mix +P10,000 1

0 70F (21C) 10

Meyers Hand Mix 72 hr. 250F (121C) 30 for > one mixtureMobil RIV Tester 2 hr. 200F (93C) 0 - 30 (Compatible)

31- 60 (Borderline)61+ (Incompatible)

Bolt &Associates

Motor Stirrer 72 hr. 250F (121C) 30 for > one mixture

ASTMD 6185

P100,000 1 248F (120C)167F (75C)

70 hr.

1400 hr. 2> about 11 above thevalue for the thickestcomponent or 11 belowthat of the thinnestcomponent

1 ASTM 60-stroke or 10,000- or 100,000- stroke worked penetration

2 Applies to low dropping point greases.

4.2 Shelf Life

In general, lubricants are very stable when exposed to the mild conditions encountered in storageor on the shelf. Storage life of many years should result. This assumes, of course, no exposureto rain, sunlight, or sources of heat such as adjacent steam lines. Why then do suppliers oftenlimit recommended shelf life to some two to three years? For several reasons:

Formulations change from time to time for supply and performance reasons base oilchanges, additive changes, and so on. Incompatibility between old and new versionssometimes is a problem. Storage life restrictions limit the supplier's responsibility for oldformulations.

Conditions of storage can vary widely and some deterioration can take place under situationsover which the supplier has no control. For example: If an oil were frozen, that is, cooled below its pour point, the solubilities of its additives

could change. In an extreme case, a part of the additive package could drop out ofsolution and perhaps not re-dissolve upon return to normal ambient temperature. Such anevent would be rare.

With greases, some cosmetic (but mostly nonfunctional) changes can take place. These relateto the problems described in Section 4.4, Continuous Versus Intermittent Use. Forexample: Age hardening, that is, hardening during the first few months of life. This occurs mostly

with soft greases consistency generally recovers on working.



4-5

Surface color change. Surface cracking from shrinking on cooling after manufacture or on heating and cooling

in storage. Bleeding, or oil separation. The separated oil can be decanted or stirred back in; it is only

a small portion of the total. This occurs mostly with soft greases made with low viscosityoils. A small amount of bleeding is acceptable. (See ASTM D 1742 for perspective.)

Suppliers' reluctance to sanction extended shelf life is understandable. Although lubricantchanges in storage are mostly cosmetic, they can be sources of many complaints. However,attention to storage conditions (including those for drums), for example, avoidance oftemperature and other environmental extremes, will eliminate virtually all the potentialproblems. A few simple tests, for example, sensory tests and infrared (see Section 5.3,Lubricant Testing) on the questionable lubricants versus an authentic sample will giveconfidence that stored material is still acceptable. Storage of the drums should be indoors ifpossible. If outdoors, drums should be out of the sun and stored with a plastic lid or on their side(bung on the upside) to avoid standing water and its leakage into the drum contents.

4.3 Time/Temperature/Radiation Considerations

Figure 4-2 shows how time, temperature, and irradiation relate to lubricant life (point at whichchange-out is necessary). The vertical scale is logarithmic and gives lubricant life in hours. Thehorizontal scale is the inverse of absolute temperature.

The slope of the band represents an approximate doubling of life for every 10C (18F)temperature decrease. One expects this for chemical reactions. The band is used to illustrate thatthe change might be more or less, depending on the chemical make-up of the lubricant. Also, thebest performing lubricants will be on the right side of the band and the poorest performinglubricants on the left. Note that the whole band moves to the right in a parallel fashion as lessstress is involved. The band moves to the left if there is more stress.



4-6

Figure 4-2Time/Temperature/Irradiation InterplayContinuous Operation in Air of High Quality Lubricant Under Stress

As an illustration, suppose a piece of equipment must be relubricated every 36 months in anapplication at 93C (200F) (A). Then at 104C (220F), the relubrication interval woulddecrease to 18 months (B). At 121C (250F), the required interval would be 9 months (C). Itwould be somewhat more than this (C') or less (C"), as the temperature effect is smaller orgreater within the band, depending on the lubricant. Note that at 66C (150F) lubricant lifewould be extended and off the chart at 300 months! Of course, lubricant life cannot be extendedindefinitely contamination from dirt, wear debris, etc., might dictate a shorter interval.

Another way to use the figure is to follow a temperature line across the band. For example, at93C (200F) the best lubricant under stress would last about 45,000 hours (D), the poorestlubricant, about one-tenth as long (E). More stress would move the band to the left and shortenlubricant life. Irradiation is one of these stresses but it takes a lot of radiation more than 107rads to shift the band appreciably.

The approximate 107 rad level is an irradiation threshold. Below it, most lubricants can tolerateirradiation. Appreciably above it, the life of most lubricants is increasingly at risk (see Section2). Similar temperature thresholds also exist for many lubricants. Up to a certain level, thermal



4-7

effects are relatively minor but, above that threshold, the thermal component of total stress canbecome increasingly large. This is tied in, of course, to the approximate doubling of chemicalreaction rate by each increase of 10C (18F) in temperature. If the rate is very low, a doublingdoesn't do much. When the reaction rate is appreciable, doubling has a discernible effect. Thethreshold is where this rate becomes apparent. Note that temperature and radiation dosethresholds are shown for various lubricants in Appendix A.

Oxidation is not addressed specifically in the figure except as an increased stress that would shiftthe band to the left. However, the lubricant life shown is for products exposed in the presence ofair. This is a normal condition and only abnormal exposure conditions, for example bubbling airthrough the lubricant, would be considered an increase in stress.

4.4 Continuous Versus Intermittent Use and Lube Performance

In any plant, much lubricated equipment operates continuously under relatively stableconditions, as when a grease lubricates a motor bearing. The life of that grease, or of the greasedbearing, can be estimated from prior experience or, more generally, from a knowledge oflubrication practice. Often such bearings can run continuously for years. Sometimes, thelubricant must be replenished at prescribed intervals. Now and then, the bearing must be replacedwhen it becomes noisy or shows other distress.

In other situations, a piece of equipment might be on stand-by status until a specified eventoccurs. Then, on signal, the equipment must quickly come up to speed and perform its function.This intermittent duty is not always benign. Start-stop operation of bearings (especially underload) can create wear debris from unusual slippage, even with proper lubrication. A spinningbearing also tends to deflect dirt, dust, and debris more readily than does a stationary unit.

Further, as a heated bearing cools after running, it tends to attract rust-producing moisture. Also,a grease in a stationary bearing can slowly separate oil from the gel, causing the lubricant to dryout. Then, too, stationary bearings are vulnerable to vibrations that can shorten bearing life dueto fretting or false brinelling (see Section 3.6). Thus, extended periods of inactivity are not goodfor long-term performance. Care must be taken to exercise the lubricated equipmentoccasionally.

When radiation is involved during lubrication, one would expect frequent operation to be moredamaging to the lubricant than intermittent operation. This is because more exposure to oxygenin the air is involved during agitation and oxidation is accelerated by irradiation. However, thisdoes not hold for greases. Their key gel structure generally benefits from shearing action(agitation) and this offsets the effect of increased oxidation.

In any event, good maintenance practices dictate that the lubricated equipment should undergo:

Periodic inspections for signs of leakage of oil, accumulation of dirt, oil thickening, greasedrying, or wear fragments in the lubricant.

Periodic exercise to assure that it functions properly without distress. This also maintainsadequate distribution of grease to lubricated parts.



4-8

Periodic lubricant changes based on experience. Lacking experience, change should be basedon intervals established in similar applications. In some instances, lubricant changeoutperiods are specified by the equipment supplier.


5-1

5 TESTS AND ANALYSES

Lubricant testing is recommended for a host of reasons. These include:

To check an incoming lubricant to verify its authenticity. To determine if a lubricant in storage is still of acceptable quality. To study the condition (wear, etc.) of the machine being lubricated. If there is a problem with

the lubricant, there is a strong possibility that the machine will need maintenance.

To determine if preventive maintenance is being performed properly and effectively. To know when it is time to relubricate the machine.

Lubricant testing is both an art and a science. The art is in determining how much science to usein addressing a concern. The full complement of lubricant tests is very broad in its scope andcomplexity but seldom is this full set of tests required. Part of the process is:

Selecting adequate and appropriate tests. Not overkilling with the unnecessary do the minimum that will resolve the concern.

5.1 Sampling

The first and most crucial step in lubricant testing is to get a representative sample. Samplesshould be taken as follows and handled carefully:

When the system is stabilized, neither just before nor just after makeup lubricant has beenadded.

Ahead of filters or centrifuges so as not to miss the contaminants that they remove. In suitable, clean, well-labeled containers. Be consistent in sampling method. Take the

sample from the same location and under the same operating conditions. In addition, beaware that sampling from the bottom of sumps, where dense materials (for example, waterand metals) settle, can give valuable information on the history of the lubrication.

5.2 Troubleshooting

Operating equipment has a great tolerance for lubricant property changes. Greases or oils canchange by a consistency grade or two and the machinery being lubricated will continue tooperate smoothly. However, an off-grade or contaminated product can hasten equipment distress,which might be manifested by:


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Temperature increase (at the lubricated part) Output decrease

Noise

Change in vibration pattern Visual indicators, for example leakage Wear and corrosion

Often the equipment distress can be anticipated by trending the data from lubricant analyses.(More details are provided on trending in Section 5.5.) Whenever any of these symptoms occur,corrective action must be taken. The action required might sometimes be evident from theinformation derived from the lubricant analysis program itself.

5.3 Lubricant Testing

The first line of surveillance in lubricant testing, or the first step in isolating a problem, is simpleon-site sensory examination. A lot can be learned from looking at, feeling, and smelling the usedlubricant. These sensory tests can signal the need for more complex laboratory tests. A hierarchy,or sequence of tests from the simple to the complex is shown in Table 5-1. Remember, do thesimple ones first!

Table 5-1Sequence of Lubricant Testing

Test Type DescriptionSensory Tests Simple tests on-site; compare to known product.Other Simple Tests Easily done on-site; again back-to-back with known product.Diagnostic Tests Laboratory; relative test - compare to known product. Skill of technician is

vital.Standard Tests Laboratory; well developed, ASTM methods formulated from round-robin

testing. Can be compared on the basis of determined repeatability andreproducibility.

Analytical Tests Laboratory; Not always standard - compare to known product. Skill oftechnician is vital. Often a judgment call is involved.

Each of these test types is discussed in detail in the following sections.

5.3.1 Sensory Tests

These tests can be performed at the plant by personnel with only limited experience. The bestsample containers for the sensory observations are 4-ounce stoppered glass bottles for oils and 2-ounce capped bottles for the greases. The stoppers/caps confine and concentrate odors fordetection. All the tests should be done at the same time that similar observations are being madeon a known, fresh, good product. Sensory tests include the following:


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Appearance: Look at the sample, as shown in Figure 5-1. Is the oil clear and bright? Or is ithazy and cloudy, indicating the presence of water? Is it foamy? Or does it show suspendedmatter? When examining grease, smear a small amount on a piece of white paper with aknife or spatula. Examine the sample for lumps and other particles, and don't forget thecomparison with the fresh, unused sample.

Color: Compare with that of the original product. This observation is sometimes useful withlight-colored materials. Darkening can indicate oxidation and/or exposure to hightemperatures. Remember that color can change by just adding the new lubricant to the systembeing lubricated!

Figure 5-1Observing the Appearance

Odor: (Figure 5-2) Again, compare with that of the original product. Oxidized oils andgreases eventually acquire an acidic, pungent, or burned smell. This occurs also at aradiation dose of about 100 megarads. The strong odor of some additives might for a timemask the developing pungent smell.

Feel: Oils should feel slippery; greases should feel buttery, not stringy or lumpy. Neithershould feel gritty, as from wear debris.

Figure 5-2Detecting the Odor


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5.3.2 Other Simple Tests Viscosity: This is a measure of the resistance to flow of an oil and is its single most

important property in hydrodynamic lubrication (see Section 3.1). The various gradingsystems for oils are given in Appendix B. Oil viscosity is generally specified by theequipment builder for operating machinery. If the viscosity is too high (thick), performancecan be sluggish because of increased drag. This also can cause increased temperature, whichhas an adverse effect on lubricants and sometimes machine life. If viscosity is too low, the oilfilm might not be able to keep the moving parts separated. In the absence of an antiwear orantiscuff additive, this can result in metal-to-metal contact, contamination with wear debris,and shorter life for both the lubricant and the machine. It is important to remember thatrotating machinery has a tolerance for everything but major changes in viscosity in service.The simplest means of determining viscosity is to compare an unknown to a known materialthrough sensory-like tests sight and feel. If this is not accurate enough for the requiredpurpose, a viscosity gage, shown in Figure 5-3, can be used. This works on the principle thatthe rate a ball falls in a column of oil depends on the viscosity of the oil.

Figure 5-3Viscosity Gage for Measuring the Viscosity of Oils(courtesy of Visgage by Louis C. Eitzen Co.)

With this device, the unknown is drawn into a tube containing a ball. A parallel tubecontaining a known oil and a like sphere is used for the comparison. After the two oils areallowed to reach equal temperatures and each ball the same starting point, the instrument isinclined at a slight angle. This starts the spheres rolling. The inclination is stopped wheneither oil's sphere reaches a calibration point. Then the position of the lagging ball in eithertube shows directly the viscosity of the unknown. Both high and low viscosity oils can beused in this equipment. Accuracy of 95% or so is achievable with little effort.

Consistency: This, as applied to a grease, is much like the viscosity of an oil a measure ofits thickness. It can be estimated in a sensory-like examination, too. Just collect a series ofgreases of known thicknesses (National Lubricating Grease Institute (NLGI) penetrations)and compare with the unknown. Use a knife or spatula to work the greases around it is easyto spot the known that matches the unknown.

Water Crackle Test: This test might be appropriate when considerable amounts of waterare suspected in the oil. A metal plate is heated to at least 120C (250F) and a few drops ofoil are added (be careful, sometimes it spatters). If the oil crackles and pops, it suggests waterin excess of 0.1-0.2%. If it simply spreads and smokes, then water concentration is low.


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Blotter Spot Test: This is most useful when a series is conducted over a period of time. Todo this test, a drop or two of a representative oil sample is put on a piece of blotter paper. It isimportant that the paper be placed so that the wetted area does not rest on a supportingsurface. After it reaches equilibrium, examine the oil spot, which might look like one of thosein Figure 5-4.

Figure 5-4Sample Blotter Spot Test

The spot is interpreted in this way: No Sludge: Oil spot fades out with indefinite boundaries. Sludge: Dispersed sludge shows up as a sharply defined outer boundary of the absorbed

oil. A well defined black inner spot indicates dispersing properties of the oil have beenoverwhelmed by sludge.

A more complex version of this test is in Section 5.3.5.

Examination of Solid Debris: When identifying the source of trouble in a machine, it isimportant to know the nature and source of solid debris in the lubricating oil. Such debris canbe separated from an oil test sample or scraped from machine parts, the oil storage tank,filters, or centrifuge bowls. The debris can then be washed free of oil with a volatilepetroleum solvent from a squeeze bottle (be aware of the fire hazard from the volatilematerial). After drying, a magnet can separate iron-derived matter from the rest. Examinationwith a 10X or stronger pocket magnifying glass or with a higher power scope, if available,will often help in deciding the nature and source of the debris. This material can be related tothe machine and its components. Results can point to needed action.

5.3.3 Diagnostic Laboratory Tests Oil Viscosity and Grease Consistency: Both of these can be measured in more complex

laboratory tests. The ASTM D 445 method is preferred for oil measurements and


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D 217 or D 1403 for grease measurements. The grease apparatus involves dropping astandard cone into a standard cup of grease. The depth of penetration is the measure ofconsistency, expressed in 0.1 millimeters. The NLGI has classified greases in grades 000 to6. The grease consistencies versus grade are given in Appendix B.

Antiscuff and Antiwear: These properties can be measured or studied in a precisionlaboratory-testing device called the Tribometer or pin-on-disk machine (ASTM G 99). A pinis pressed against a rotating disk. Friction coefficients and wear on the pin and on the disk aremeasured. Various metal combinations can be used and various test conditions imposed, forexample load, speed, surface finish, and temperature. (See Section 6, Lubricating MotorizedValve Actuators, Table 6-3, for typical data from the Tribometer.)

Infrared Spectroscopy (IR): In this lab procedure, a beam of infrared light is passedthrough or bounced off a thin film of an organic material, for example a lubricant. Thevarious chemical functional grou

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EPRI_Lubrication Guide 1003085