Lubrication Guide Revision 3 (Formerly NP-4916-R2)
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Technical Report
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Lubrication Guide Revision 3 (Formerly NP-4916-R2) 1003085
Final Report, October 2001
EPRI Project Manager M. Pugh
EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA 800.313.3774 • 650.855.2121 •
[email protected] • www.epri.com
DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(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, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL PROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'S CIRCUMSTANCE; OR (B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT. ORGANIZATION(S) THAT PREPARED THIS DOCUMENT Bolt & Associates
ORDERING INFORMATION Requests 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 Power Research Institute, Inc. EPRI. ELECTRIFY THE WORLD is a service mark of the Electric Power Research Institute, Inc. Copyright © 2001 Electric Power Research Institute, Inc. All rights reserved.
CITATIONS This report was prepared by Nuclear Maintenance Applications Center (NMAC) EPRI 1300 W.T. Harris Boulevard Charlotte, 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.
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REPORT SUMMARY
A large number of lubricants are used in power plants for various purposes. Maintenance personnel need concise guidelines for selecting the correct lubricant for a specific application. Also, specific knowledge is required regarding a lubricant’s characteristics to determine its applicability. Background This lubrication guide has traditionally provided useful information to power plant personnel involved in this area of plant operation and maintenance. This revision of the Lubrication Guide incorporates changes within the lubrication industry including consolidation and discontinuation of product lines and features. As in Revision 2, it also includes topics that were covered under EPRI 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
Results This guide addresses lubricants, lubrication, testing, and friction and wear. It includes sections on basic lubrication, application problems, tests and analysis. Tables are provided that profile each use category, listed lubricants for specific applications, and temperature and radiation tolerances of these lubricants. A glossary of technical terms is also included. Guidance on selecting the correct lubricant for a specific application is also provided. Information on determining the remaining life of a lubricant is addressed, which can help reduce unnecessary and costly lubricant change-outs. EPRI Perspective Knowledge of lubrication is important to maintenance personnel in their day-to-day work. This guide provides, in a concise form, a substantial amount of information on properties of commonly used lubricants. Selection of correct and compatible lubricants can help prevent unscheduled maintenance or shutdown. Information contained in this guide can be useful to a training instructor and to persons being initiated in the technology of lubrication. This revision to the NMAC Lubrication Guide attempts to incorporate recent changes within the lubrication industry including consolidation and discontinuation of product lines and features.
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Keywords Plant engineering Plant maintenance Plant operations Lubricants Lubrication
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ACKNOWLEDGMENTS This publication was developed by the Nuclear Maintenance Application Center (NMAC). The first versions of the Guide were prepared by Dr. Bob Bolt and the late Jim Carroll. This third version, built on the prior work, was prepared largely by Dr. Bolt with the major assistance of Dr. Howard Adams. Additionally, Dr. Bolt would like to acknowledge the valuable contributions from the following: Chesley Brown Jim Fitch Doug Godfrey Bill Herguth Steve Mitchell
TXU Noria Wear Analysis; Bolt & Associates Herguth Laboratories AEP
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ABSTRACT This Guide gives information on lubricants from many manufacturers, suitable for various nuclear power plant applications. Lubricant operating limits with respect to temperature and radiation dose are listed. The Guide also addresses the basics of how lubricants work, how radiation affects them, and how this relates to their composition. Friction and wear is another basic topic presented, along with lubricant stress effects, shelf life, compatibility, troubleshooting and testing, all important in maintenance. The testing section has received particular attention with the addition of several new test methods. A summary of the lubricants study in the EPRI/Utilities Motor-Operated Valve Performance Prediction Program is also included, as it was in Revision 2. The Guide is intended for use by power plant maintenance and engineering personnel.
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CONTENTS
1 LUBRICANTS: WHAT THEY ARE AND HOW THEY WORK ............................................. 1-1 1.1
Base Oils................................................................................................................... 1-1
1.2
Key Measurements ................................................................................................... 1-2
1.3
Additives ................................................................................................................... 1-3
1.3.1 Vl Improvers ......................................................................................................... 1-4 1.3.2 Detergent/Dispersants .......................................................................................... 1-4 1.3.3 Basic Metal Compounds....................................................................................... 1-4 1.3.4 Antiwear and Antiscuff (EP) Additives................................................................... 1-4 1.3.5 Antioxidants.......................................................................................................... 1-5 1.3.6 Rust Inhibitors and Antifoamants .......................................................................... 1-6 1.3.7 Gelling Agents ...................................................................................................... 1-6 1.4
Synthetic Lubricants.................................................................................................. 1-6
2 RADIATION EFFECTS ON LUBRICANTS.......................................................................... 2-1 2.1
Effect on Elastomers ................................................................................................. 2-8
3 LUBRICATION, FRICTION, AND WEAR ............................................................................ 3-1 3.1
Hydrodynamic Lubrication (HDL)............................................................................... 3-1
3.2
Elastohydrodynamic Lubrication (EHL) ..................................................................... 3-2
3.3
Boundary Lubrication (BL)......................................................................................... 3-3
3.3.1 Physically Adsorbed Film...................................................................................... 3-3 3.3.2 Chemisorbed Film ................................................................................................ 3-4 3.3.3 Chemical Reaction Film ........................................................................................ 3-5 3.4
Solid Lubricants......................................................................................................... 3-5
3.5
Nature of Machined Surfaces.................................................................................... 3-6
3.6
Wear ......................................................................................................................... 3-6
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4 APPLICATION PROBLEMS................................................................................................ 4-1 4.1
Compatibility of Mixed Products ................................................................................ 4-1
4.1.1 Oils ....................................................................................................................... 4-1 4.1.2 Greases................................................................................................................ 4-1 4.2
Shelf Life ................................................................................................................... 4-4
4.3
Time/Temperature/Radiation Considerations ............................................................ 4-5
4.4
Continuous Versus Intermittent Use and Lube Performance..................................... 4-7
5 TESTS AND ANALYSES .................................................................................................... 5-1 5.1
Sampling ................................................................................................................... 5-1
5.2 5.3
Troubleshooting ........................................................................................................ 5-1 Lubricant Testing....................................................................................................... 5-2
5.3.1 Sensory Tests ...................................................................................................... 5-2 5.3.2 Other Simple Tests............................................................................................... 5-4 5.3.3 Diagnostic Laboratory Tests ................................................................................. 5-5 5.3.4 Standard Laboratory Tests ................................................................................. 5-12 5.3.5 Analytical Test Methods...................................................................................... 5-14 5.4 Using Test Results .................................................................................................. 5-19 5.5
Trending.................................................................................................................. 5-19
5.6 5.7
Warning Limits ........................................................................................................ 5-20 Cleanup Considerations .......................................................................................... 5-22
6 LUBRICATING MOTORIZED VALVE ACTUATORS .......................................................... 6-1 6.1 Stem Nut Friction and Wear – Off-the-Shelf Products ............................................... 6-2 6.2 Stem Nut Friction & Wear – Solid Lubricants and Improved Nut Cutting Procedure........................................................................................................................... 6-4 6.3
Search for Improved Actuator Lubricants .................................................................. 6-6
6.4
Long-Term Thermal Effects On Greases................................................................... 6-9
6.5
Conclusions ............................................................................................................ 6-11
A APPENDIX A....................................................................................................................... A-1 A.1
Lubricant Property Tables ......................................................................................... A-1
A.2
Footnotes. ............................................................................................................... A-14
B APPENDIX B ......................................................................................................................B-1 B.1
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Glossary.................................................................................................................... B-1
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LIST OF FIGURES Figure 1-1 Effect of Antiwear and Antiscuff Additives .............................................................. 1-5 Figure 1-2 Hydrocarbon Oxidation Process............................................................................. 1-6 Figure 2-1 Dose Levels for Radiation Effects .......................................................................... 2-1 Figure 2-2 Interaction of a Gamma Photon with Organic Matter.............................................. 2-2 Figure 2-3 Upper Limits of Radiation Doses Resulting in Failure of Various Base Fluids ........ 2-3 Figure 2-4 Radiolysis Effects on a Lithium Complex-Gelled, Mineral Oil-Based Grease.......... 2-4 Figure 2-5 Relative Oxidation Stability of Irradiated Mineral Oil-Based Steam Turbine Oils in Turbine Oil Stability Tests (TOST) (ASTM D 943) ................................................. 2-5 Figure 2-6 Effect of Temperature and Irradiation on Bearing Life of a Sodium SaltThickened, Mineral Oil-Based Grease ............................................................................. 2-6 Figure 2-7 Relative Sensitivity of Common Lubricants and Elastomers to Irradiation .............. 2-8 Figure 2-8 Resistance of Elastomers to Irradiation.................................................................. 2-9 Figure 3-1 Hydrodynamic Lubrication...................................................................................... 3-2 Figure 3-2 Elastohydrodynamic Lubrication ............................................................................ 3-2 Figure 3-3 Boundary Lubrication (Fragmented Roughness) .................................................... 3-3 Figure 3-4 Representation of Physically Adsorbed Film—Non-Polar Molecules ...................... 3-4 Figure 3-5 Physically Adsorbed Film—Polar Molecules .......................................................... 3-4 Figure 3-6 Chemisorbed Film .................................................................................................. 3-4 Figure 3-7 Effects of Various Parameters on Friction Coefficient............................................. 3-5 Figure 3-8 Machined Surface .................................................................................................. 3-6 Figure 4-1 Compatibility of Mixtures of Greases With Different Gelling Agents........................ 4-3 Figure 4-2 Time/Temperature/Irradiation Interplay Continuous Operation in Air of High Quality Lubricant Under Stress........................................................................................ 4-6 Figure 5-1 Observing the Appearance..................................................................................... 5-3 Figure 5-2 Detecting the Odor................................................................................................. 5-3 Figure 5-3 Viscosity Gage for Measuring the Viscosity of Oils................................................. 5-4 Figure 5-4 Sample Blotter Spot Test ....................................................................................... 5-5 Figure 5-5 Wear Particle Size/Concentration and Machine Condition ..................................... 5-8 Figure 5-6 Detection of Wear and Other Particles ................................................................... 5-9 Figure 5-7 Schematic of TGA Setup...................................................................................... 5-15 Figure 5-8 Schematic of DSC Apparatus............................................................................... 5-15 Figure 5-9 Ruler™ (Remaining Useful Life Evaluation Routine) Instrument .......................... 5-16
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Figure 5-10 Example of Three Additives and Voltammeter Response................................... 5-17 Figure 5-11 Chromatographs of Fresh and Used Gear Oils .................................................. 5-18 Figure 5-12 Sample Plot of Lubricant Properties................................................................... 5-20 Figure 6-1 Composite of Friction Coefficient (@10,000 lbs) Versus Number of Strokes .......... 6-4 Figure 6-2 Cross-Section of Macrograph of New SMB-O Stem Nut Thread – Standard Machining........................................................................................................................ 6-5 Figure 6-3 Pin-On-Disk Machine Schematic (Tribometer) ....................................................... 6-7
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LIST OF TABLES Table 1-1 Oil and Grease Requirements ................................................................................. 1-1 Table 1-2 Common Additives in Various Lubricants ................................................................ 1-3 Table 1-3 Synthetic Base Oils and Their Application ............................................................... 1-7 Table 1-4 Comparative Properties of PAO Synthetic Base Oil and Various Mineral Base Oils.................................................................................................................................. 1-8 Table 2-1 Effects of Irradiation on Common Oils ..................................................................... 2-7 Table 2-2 Effects of Irradiation on Common Greases.............................................................. 2-7 Table 2-3 Resistance of Elastomers to Effects of Common Oils and Greases......................... 2-8 Table 4-1 Compatibility of Greases ......................................................................................... 4-2 Table 4-2 Grease Compatibility Tests ..................................................................................... 4-4 Table 5-1 Sequence of Lubricant Testing................................................................................ 5-2 Table 5-2 IR Peak Regions of Interest..................................................................................... 5-6 Table 5-3 Sources of Metals in Lubricants .............................................................................. 5-8 Table 5-4 Wear and Its Causes............................................................................................... 5-9 Table 5-5 Range Number Determination............................................................................... 5-11 Table 5-6 Key Tests for Lubricants........................................................................................ 5-13 Table 5-7 Typical Warning Limits for Certain Lubricant Services........................................... 5-21 Table 6-1 Friction and Wear Performance Summary (500 Stroke Stem/Stem Nut Lubricant Tests with SMB-0)............................................................................................ 6-3 Table 6-2 Bleeding Tests on Grade 1 Greases (including effects of gelling agents) ................ 6-6 Table 6-3 Pin-on-Disk Tribometer Data for Some Grease Types............................................. 6-8 Table 6-4 Grease Consistency Changes in Long-Term Thermal Tests ................................. 6-10 Table A-1 Turbine Oils ISO Viscosity Grades 32, 46, 68 ........................................................ A-1 Table A-2 Engine Oils for Large Diesels................................................................................. A-2 Table A-3 Low-Pressure Hydraulic Oil ISO Viscosity Grades 32, 46, 68, 100......................... A-3 Table A-4 High-Pressure Hydraulic Oil ISO Viscosity Grades 32, 46, 68, 100........................ A-4 Table A-5 Compressor Oils .................................................................................................... A-5 Table A-6 High Load Extreme Pressure (EP) Gear Lubricants ............................................... A-6 Table A-7 Open Gear Lubricants............................................................................................ A-7 Table A-8 Antiseizure Compounds ......................................................................................... A-8 Table A-9 Limitorque Valve Actuator Lubricants..................................................................... A-9 Table A-10 Fire Resistant Hydraulic Fluids .......................................................................... A-10
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Table A-11 General Purpose Greases—Grades 00, 0, 1, 2, 3.............................................. A-11 Table A-12 Coupling Greases .............................................................................................. A-12 Table A-13 Grease Types and Performance ........................................................................ A-13 Table B-1 Viscosity Equivalents ............................................................................................. B-4
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1 LUBRICANTS: WHAT THEY ARE AND HOW THEY WORK
Oils and greases have to meet the several requirements shown in Table 1-1. Table 1-1 Oil 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 from the semi-solid nature of greases. On the other hand, there are several functions exclusive to oils that are derived from their fluid nature.
1.1
Base Oils
To perform the indicated tasks, commercial lubricating oils consist of about 85 to 99+ % base oil. The remainder consists of additives. Additives are used to enhance the properties of the base oil or to create a necessary property in it. Base oils are classified as:
• Mineral oils • Synthetic oils
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EPRI Licensed Material Lubricants: What They Are and How They Work
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 of synthetic-based lubricants is 3-8 times the cost of mineral oil-based products. (For additional discussion on synthetic lubricants, see Section 1.4.) The term “mineral oil,” as opposed to “synthetic oil,” implies that little processing is involved in the manufacture of mineral base oils. This is not true. The fraction distilled from selected petroleum crude oils for subsequent base oil manufacture contains many organic molecular species. Several of these must be removed to yield a high quality final base oil. Aromatic and wax compounds are two classes that are removed. Aromatics (alternating carbon-to-carbon double bonds in six membered rings) show a particularly high rate of viscosity change with temperature. This is not a good property in a lubricant. Waxes are solids at room temperature and are, therefore, unsuitable in base oils. Removing these requires considerable processing. Physical treatment, for example solvent refining, is still used as a method of removal, but catalytic hydrogenation 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 mild catalytic hydrogenation yields a Group II base oil, while more rigorous hydrogenation produces a Group III base material. Some properties of these and of a common synthetic hydrocarbon base oil (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 in centistokes (cSt.). The viscosity at 40°C is used in industrial oil grading. For example, a 32 grade has a viscosity at 40°C of around 32 cSt. Other grading methods exist but they are used primarily for 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 in petroleum antiquity. An oil derived from a Gulf Coast crude oil showed a high rate of change of viscosity with temperature and was arbitrarily given a VI value of 0. A Pennsylvania crudederived oil, with a low rate of change of viscosity with temperature, was given a VI of 100. All oils 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 refined mineral oils (Group III, some Group IIs) can have VIs in the 105 to 160 range, reflecting their superior viscosity/temperature properties. Temperature Viscosity Coefficient (λ λ) is a more fundamental indication of change of viscosity with temperature, which may soon become more widely used. It is (see Table 1-4 for some values): λ = viscosity in cSt at 40°C – viscosity in cSt at 100°C viscosity in cSt at 40°C Grease consistency is measured by “penetration” values. These are determined from the distance (in 0.1 mm units) that a standard American Society for Testing and Materials (ASTM) 1-2
EPRI Licensed Material Lubricants: What They Are and How They Work
cone sinks into a standard cup of grease at 77°F (25°C). Because consistency can change with shear or “working,” greases are often worked in a standard worker before penetrations are measured. The worked penetrations corresponding to the various grease grades are shown in the Glossary (Appendix B). P60 refers to the penetration after 60 double strokes in the worker; P 10,000 refers to 10,000 double strokes, and so on. Grease grades are determined by P 60 values (see Appendix B for grade determinations). Dropping Point is another ASTM grease measurement. It is the temperature at which a grease just 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 to create properties or enhance those that already exist. Table 1-2 shows finished lubricants and the additives they might contain. Table 1-2 Common Additives in Various Lubricants Common Lubricants
Engine Oils Gasoline
Diesel
VI Improvers
x
x
Detergent/Dispersants
x
x
Basic Metal Compounds
x
x
Antiwear Agents
x
x
Turbine Oils
Hydr. Oils
Gear Oils
Compr. Oils
x
x
Greases
Additives
x x
x
Antiscuff (EP) Agents
x
x
x
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.
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EPRI Licensed Material Lubricants: What They Are and How They Work
1.3.1 Vl Improvers Viscosity Index (VI) improvers are listed first because they are used in the largest amounts to perform their function. They thicken lower viscosity base oils and, in the process, flatten the mixture's viscosity/temperature slope. This improves VI. These additives are widely used to make mineral oil-based multigrade engine oils. VI improvers are not required to make multigrade products from synthetic base oils or some Group III mineral base oils. This is because of 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 plug piston rings, key oil passages, etc. or collecting as sludge. Detergent/dispersants were among the first additives used and continue to be of high importance in engine oils where deposits can come from 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 their main function is to neutralize acids in diesel engine oils. The acids come from the combustion of sulfur in fuel and the fixation of nitrogen in combustion air. Reaction with water converts the sulfur and nitrogen oxides to corresponding acids. If not neutralized, they cause corrosive wear of engine parts. The need for basic metal compounds (base reserve, high base number) in part depends on the sulfur content of the fuel – the lower the sulfur the less need for base. The national trend toward low sulfur diesel fuel to control emissions will eventually reduce the use of basic metal compounds. 1.3.4 Antiwear and Antiscuff (EP1) Additives Antiwear additives are very widely used in engine and industrial lubricants, but not universally so. Antioxidants, on the other hand, are universally used. Antiscuff additives are less widely used, 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 additives function by interposing a relatively shear-resistant chemical film between load bearing metal 2 surfaces. The general mechanism by which these additives work is shown in Figure l-l . At the top, two moving metal surfaces under little or no load are held apart by an oil film. With the 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 most common antiwear agents and they form films of iron, sulfur, and phosphorus compounds to protect 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.
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EPRI Licensed Material Lubricants: What They Are and How They Work
antiscuff agents. All of these additives act similarly in both oils and greases and they can be temperature-sensitive. Mild antiwear can also be provided in greases from the gelling agents.
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Figure 1-1 Effect of Antiwear and Antiscuff Additives
1.3.5 Antioxidants The principal enemy of any lubricant is oxidation. The onset of oxidation cannot be prevented but only delayed. The delay is called the induction period. Antioxidants extend the induction period very effectively. Once this period is exceeded, however, oxidation can occur exponentially, 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 18°F (10°C). However, doubling a very low rate still yields a low rate and the rate is low during the induction period.
3
Footnote refers to q, Appendix A, Section A.2.
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EPRI Licensed Material Lubricants: What They Are and How They Work
Figure 1-2 Hydrocarbon Oxidation Process
1.3.6 Rust Inhibitors and Antifoamants Rust or corrosion inhibitors are also widely used. They perform by forming a weakly adsorbed film on the surfaces to be protected. An antifoamant is also used in most oils. They are polymers and silicone fluids in low concentration, which affect surface tension to reduce the foaming tendency. They also help provide good deaeration properties. Recently, there is a move away from silicone antifoam materials for oils, for example, turbine oils. This is because there can be tight 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 its unique stay-in-place function. The oil that is gelled also contains the other additives required to provide the necessary properties shown in Table 1-2. In addition, the gelling agent identity defines many of the grease's other performance characteristics. These are detailed in Appendix A, Table A-13.
1.4
Synthetic Lubricants
Synthetic lubricants are man-made lubricants whose base oils are chemical products manufactured or “synthesized” to provide properties not available in Group I and some Group II mineral-oil-based products. Although the synthetics represent less than one percent of the total lubricant inventory, they are available for and are used in many applications. Table 1-3 shows the various classes of synthetic base oils and the finished products in which they are used.
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EPRI Licensed Material Lubricants: What They Are and How They Work Table 1-3 1 Synthetic Base Oils and Their Application Engine Oils
Jet
Industrial Oils
Greases
Fire Resistant Oils
Relative 2 Cost
Other
Synthetic Oils Poly(alpha-olefins) (PAOs)
x
Diesters
x
Polyolesters
x
3
x
3
4-8
4
5-7
x
x
10-14
Phosphate Esters
x
Polyethers (Polyglycols)
x
Silicones 7 (Siloxanes)
x
6
Perfluoropolyethers Polyphenylethers Chlorofluorocarbons
10 6-8
6
x
x x
5
30-100
x
x
80-800 100+
x
100+
1
In the field of metalworking/cutting fluids, water-based fluids are sometimes called “synthetic.” 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. 2
The poly(alpha-olefins) (PAOs - Group IV) are the most widely used synthetic base oils in industrial and automotive lubricants. However, the differences between them and the new highly refined (hydrocracked4) mineral oil base stocks (Group III) are becoming blurred as shown in Table 1-4. Because of this, the marketplace is likely to see fewer PAO-based products in the future. The hydrocracked base oils cost half as much as the PAOs and their properties are often similar.
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 in the polymerization of the alpha-olefins (PAOs). The severity of the process dictates the properties of the final product as in Table 1-4.
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EPRI Licensed Material Lubricants: What They Are and How They Work Table 1-4 Comparative Properties of PAO Synthetic Base Oil and Various Mineral Base Oils Mineral Oils Group I*
Mineral Oils Group II*
Mineral Oils Group III*
PAO API Group IV*
Viscosity, 40°C, cSt
32
44
39
32
Viscosity, 100°C, 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 204°C)
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. The lower 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. Here the PAO and Group II and III oils are inferior to the normal, or Group I, mineral oil. That is, if sludge 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 IIIbased product. This is because the Group II, III, and IV oils generally give a higher degree of oxidation 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 products unless the application demands their superior properties. For example, if equipment needing lubrication is used in subzero weather, it is worth the added cost reliably to start or operate the frigid apparatus with a PAO-based oil. The cost, of course, is only half as much if a Group IIIbased product can be used. In another example, if fire-resistant oil is needed, then the additional cost is justified. But if these properties are not required, there is no need to use expensive synthetic products. The vast majority of the nuclear power plant lubrication requirements can be met with high quality mineral oil-based products.
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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 an added stress. Overall effects of thermal and radiation exposures are similar. For example, both show 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 and other structural changes. Gas evolution also takes place early, followed by changes in fluidity as secondary reactions take over. The final product of very high thermal or radiation exposure is an intractable solid, no longer a lubricant. Radiation effects are directly related to the radiation energy input. This input is expressed in terms of the rad (100 ergs/gram of absorber = 4.3 X 10 -6 Btu/lb). The radiation sensitivity of lubricants versus other things is shown in Figure 2-1. The more complex the irradiated object the less tolerant it is of irradiation. Note the effect on the ultimate in complexity – homo sapiens!
Figure 2-1 Dose 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).
2-1
EPRI Licensed Material Radiation Effects on Lubricants
Mechanistically, incident gamma radiation affects organic matter through initial collisions with electrons of individual atoms of molecules. This is shown in Figure 2-2. About half an incoming ray's energy is given up to a scattered electron and the weakened gamma ray goes on to repeat the process. The charged electron, knocked from its position by the incoming gamma ray, goes on to lose its added energy by creating increasingly intense ionizations and excitations in neighboring molecules.
Figure 2-2 Interaction of a Gamma Photon with Organic Matter
Incident high energy neutrons interact initially with atomic nuclei of irradiated material instead of with the electrons in gamma ray interactions. This knocks out protons and these charged particles 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 that result in new molecular products occur in the next 10 -2 seconds. To minimize change, excitation without decomposition needs to be fostered. Use of additives, for example selected compounds containing 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 through the generation of heat (resonance), that is, aromatic compounds. Thus, the effect on lubricants depends on the chemical makeup of both the base oil and additives. Figure 2-3 shows this for base oils.
2-2
EPRI Licensed Material Radiation Effects on Lubricants
Figure 2-3 Upper Limits of Radiation Doses Resulting in Failure of Various Base Fluids
Note the effect of aromatic content – the polyphenyls, poly(phenyl ethers), and alkylaromatics head the list in radiation resistance. Phenyl groups are basic units of aromaticity. Aromatics, because of their poor viscosity/temperature properties, are deliberately removed from mineral base oils. However, aromatic compounds can be designed through synthesis to have good properties. Such materials (alkylaromatics) are employed in making lubricants designed for maximum radiation resistance. The introduction of phenyl groups even into poor performing molecules will improve their radiation resistance. For example, phenyl silicones are a notch better 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 hardening as the effect on the oil component takes over. Figure 2-4 shows the typical softening effect. Although this grease exhibits stability in the 10 6-108 rad region, other greases can either harden or soften in this region. This is before the major softening indicated in Figure 2-4 and before effects on the oil component set in.
2-3
EPRI Licensed Material Radiation Effects on Lubricants
Figure 2-4 Radiolysis 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 in Figure 2-5. Other effects on oils include gas evolution, evidenced by a decrease in flash point and increase in vapor pressure. The gas is hydrogen and low molecular weight hydrocarbons that come from C-H and C-C bond fissure. The C-C bond breakage can also yield compounds that eventually “double” or similarly polymerize to cause viscosity increase.
2-4
EPRI Licensed Material Radiation Effects on Lubricants
Figure 2-5 Relative Oxidation Stability of Irradiated Mineral Oil-Based Steam Turbine Oils in Turbine Oil Stability Tests (TOST) (ASTM D 943)
The effect of radiation dose rate is also highlighted in Figure 2-5. The doses shown were delivered to the test samples at widely different rates – differing by a factor of about one thousand. Yet the variation in the test results falls within the reproducibility limits of the ASTM D 9436 test. Thus, there appears to be no appreciable dose rate effect. All the exposures were made in air for the indicated doses and then the oils were tested. Note that the dose below which no significant oxidation takes place is about 5 X 10 6 rads. This dose rate concern comes up primarily in applying radiation effects studies to plant situations. Most radiation effects studies are accelerated, that is, at higher dose rates than those in the 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 under irradiation. Oxidation is mitigated by oxidation inhibitors. All high quality lubricants have such antioxidants. 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 an important consideration from a maintenance point of view. Lubricant life will be reduced if there is excessive exposure to oxygen in the air, for example, where there are unrepaired air leaks on the inlet side of a pump in a radioactive area. In the example, a rich supply of oxygen and irradiation 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)].
2-5
EPRI Licensed Material Radiation Effects on Lubricants
Generally, radiolysis of lubricants is not a problem in nuclear power plants. It takes radiation doses above those prevailing in normal nuclear plant operations to make appreciable changes in bulk properties of lubricants. An accident scenario (a DBA) may produce high enough radiation exposure to cause significant property changes. In such a case, the equipment being lubricated doesn't have to operate very long or be maintained. The equipment itself is very tolerant of fluidity changes in lubricants. For example, antifriction bearings in motors can go just fine, at least in the short run, with grease worked penetrations from about 200 to over 400. This is equivalent 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 rpm bearing at various temperatures. An Arrhenius plot (log bearing life versus inverse of absolute temperature) is shown. Note the change in life of irradiated grease versus that of unirradiated product. 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. 7 Tests as per ASTM D 3336 were then run on the greases. Figure 2-6 Effect of Temperature and Irradiation on Bearing Life of a Sodium Salt-Thickened, Mineral Oil-Based Grease
7
ASTM D 3336, “Test Method for Life of Lubricating Greases in Ball Bearings at Elevated Temperatures.”
2-6
EPRI Licensed Material Radiation Effects on Lubricants
The effects of irradiation on oils and greases are summarized in Tables 2-1 and 2-2. Table 2-1 Effects of Irradiation on Common Oils Radiation Dose 6
< 10 Rads
Effect No unusual problems.
6
7
Things begin to happen; some turbine oils borderline.
7
8
Most oils usable; some marginal.
8
9
The best oils usable; most become unusable.
9
10
Only special products will work.
10 - 10 Rads
10 - 10 Rads
10 - 10 Rads
10 - 10 10
> 10
No oil usable.
Table 2-2 Effects of Irradiation on Common Greases Radiation Dose 6
< 10 Rads
Effect No unusual problems.
6
7
Things begin to happen; some greases borderline.
7
8
Most high quality products usable; others not.
8
9
Most greases unusable.
10 - 10 Rads 10 - 10 Rads 10 - 10 Rads 9
9
10 - 5 x 10 Rads 9
> 5 x 10 Rads
Special products required. No grease usable.
Values for temperature and radiation operating ranges are given for individual products in Appendix A, Tables A1-A12. In these tables, the first number listed in each category is the value below which little, if any, property change will occur and long use life can be expected. The second number is the point where appreciable change is expected and surveillance of the equipment is required. The need for lubricant changeout should be anticipated at this point.
2-7
EPRI Licensed Material Radiation Effects on Lubricants
2.1
Effect on Elastomers
Elastomers are used frequently as seal materials in nuclear power plants. If one is concerned with radiation-resistance, elastomers are the weak link. Figure 2-7 shows the resistance to irradiation of elastomers versus lubricants. The elastomers are about ten times more sensitive to radiation than lubricants.
Figure 2-7 Relative Sensitivity of Common Lubricants and Elastomers to Irradiation
Table 2-3 shows the effect of common lubricants on various elastomers. Neoprene and Nitrile rubber and the epichlorohydrins are the principal oil and grease resistant products. Table 2-3 Resistance of Elastomers to Effects of Common Oils and Greases Elastomer
2-8
Resistance
Natural Rubber
Very Poor
Neoprene
Good - Excellent
Ethylene/propylene
Very Poor
Isoprene
Very Poor
Nitrile (high)
Excellent
Epichlorohydrin
Excellent
Urethane
Fair - Excellent
Silicone
Fair - Poor
EPRI Licensed Material Radiation Effects on Lubricants
The picture changes somewhat as the elastomers are exposed to radiation. Figure 2-8 illustrates this performance. The natural rubbers and urethanes are most resistant to radiation, with the nitriles ranked a close second.
Figure 2-8 Resistance of Elastomers to Irradiation
2-9
EPRI Licensed Material
3 LUBRICATION, FRICTION, AND WEAR
Three lubrication mechanisms have been established in tribology – the study of surfaces in relative 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 exist depending on geometry and/or operating conditions. For example, the balls in ball bearings involve EHL in their relationship to the bearing races and BL in their relationship to the cages or retainers. It is important to understand the three types of lubrication in order to be clear about lubricants and how they function. Friction is the resistance to the relative motion of surfaces and is an indicator of the efficiency of this motion. It is important because poor efficiency relates to high energy consumption. Wear, or the undesirable removal of material from contacting surfaces due to relative motion, shortens equipment life and decreases its reliability.
3.1
Hydrodynamic Lubrication (HDL)
HDL conditions exist when a fluid film completely separates moving surfaces and there is no surface-to-surface contact. This is the most desirable regime of lubrication because friction and wear are low under these conditions. HDL is the most common mode of lubrication for components of industrial machines. Examples include simple journal bearings and bushings, and turbine shaft bearings. Factors affecting HDL are the viscosity of the lubricating fluid, its adhesion to the surfaces, the sliding or rolling velocity of the components, the shape of the surfaces, and pressure (load) between them. Film thicknesses for effective HDL range from 0.0001 to 0.005 inches (40-200 microns). The creation of such films is fostered when the shape of the surfaces allows a wedge of lubricant to form between them (see Figure 3-1). The failure of HDL usually results from too thin a film, due to high temperatures, that reduces the viscosity of fluids, low speed that discourages wedge formation, and shock loads. Another very common cause of film failure is damage by contaminants, such as dirt, in the oil .
3-1
EPRI Licensed Material Lubrication, Friction, and Wear
Figure 3-1 Hydrodynamic Lubrication
3.2
Elastohydrodynamic Lubrication (EHL)
The name, elastohydrodynamic, implies that a full oil film exists between moving surfaces that are elastically deformed. EHL occurs only in situations where loads are concentrated over small areas, for example between balls/rollers and races in rolling element bearings and between gear teeth. In EHL the load is sufficient to deform the surfaces elastically at the point or line of near contact (Figure 3-2). The oil is trapped between the deformed surfaces and the resulting high pressure increases the oil's viscosity by several orders of magnitude. The surface deformation also increases the load bearing area. The combination of extremely high oil viscosity and increased area over which the load is applied keeps the surfaces from touching .
Figure 3-2 Elastohydrodynamic Lubrication
Lubricant film thickness in EHL is smaller than in HDL and the thinner the film for a given oil viscosity the higher the friction. As with HDL, conditions that make for thinner films shorten component life in EHL. High temperatures and loads, low speed or oscillatory operation, and especially 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. 3-2
EPRI Licensed Material Lubrication, Friction, and Wear
Because of the cyclic elastic deformation, fatigue cracks and pits are formed. This contact fatigue determines 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 Figure 3-3). The word, boundary, suggests surface involvement. BL occurs with high loads and temperatures, low sliding velocities, and rough surfaces. Examples of BL are bearings during start up and shut down, oscillating bearings, piston rings at top-dead-center, worm gears, and metal cutting operations. Friction and wear in BL are dependent upon the shape and composition of the surfaces and the properties of the lubricant. Friction results from the shear of the interfacial material, which includes adhesion between the surfaces and the shear of other solids or liquids in the contact. For example, if the additives in an oil form a soap film of low shear strength 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 3-3 Boundary Lubrication (Fragmented Roughness)
3.3.1 Physically Adsorbed Film Physically adsorbed film involves the adsorption of the non-polar molecules of the base oil at random on the surfaces (see Figure 3-4). The adsorption is reversible so, as temperature increases, the film desorbs and fails to keep the asperities in the surfaces apart (for asperities, see Section 3.5). Mineral oils or PAO synthetic base oils are in this category. If the oil molecules are polar, for example a polyester synthetic, their adsorption is stronger because of their close packed nature (see Figure 3-5). Higher temperatures are required to desorb them.
3-3
EPRI Licensed Material Lubrication, Friction, and Wear
Figure 3-4 Representation of Physically Adsorbed Film—Non-Polar Molecules
Figure 3-5 Physically Adsorbed Film—Polar Molecules
3.3.2 Chemisorbed Film Chemisorbed films (see Figure 3-6) are chemical reaction products between long chain polar compounds 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 surface to form a soap. The reaction is irreversible so an increase in temperature increases its rate. The melting point of the soap film is the temperature limitation. The additives in an oil that chemisorb are termed lubricity additives because they reduce friction as compared to that of the base oil alone.
Figure 3-6 Chemisorbed Film (Xs indicate chemical bond)
3-4
EPRI Licensed Material Lubrication, Friction, and Wear
3.3.3 Chemical Reaction Film Chemical reaction films are also formed through irreversible reactions but the products are inorganic salts. Additives such as sulfur compounds react with surfaces containing iron to form iron sulfide. Such high melting point compounds inhibit scuffing by preventing bare metal-tometal contact. They are called antiscuff (formerly known as EP) additives. Oxygen, which is in oils from the air, can also act as an antiscuff agent by reacting with metals to form thicker oxide films and prevent metal-to-metal contact. The relationship between HDL and boundary lubrication (BL) for various operating conditions is shown in Figure 3-7. Note the effects of the various parameters on the friction coefficient. With a given speed and load, a low viscosity oil will allow boundary lubrication and a very high viscosity oil will increase fluid friction.
Figure 3-7 Effects 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-surface contact. It might also reduce friction and wear. Solid lubricants are classified as follows: •
The metal oxides that form in air, for example iron oxide, Fe 3O4, on steel (which reduces friction), or aluminum oxide (which increases friction).
•
Preformed coatings such as soft lead or Babbitt on aluminum in a journal bearing, the laminar graphite or molybdenum disulfide on steel, or poly(tetrafluoroethylene) (Teflon) on steel.
•
Boundary lubricant films such as soap from a fatty acid in the oil, or iron phosphate from tricresyl phosphate additive, iron borate from boron additive compound, or iron sulfide from a sulfur additive compound in the oil.
•
Inorganic conversion coatings such as iron/manganese phosphate on steel. 3-5
EPRI Licensed Material Lubrication, Friction, and Wear
3.5
Nature of Machined Surfaces8
Machined metallic surfaces are rough on a microscopic scale (see Figure 3-8) and covered with a thin 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 asperities touch) is much less than the apparent area of contact. This real contact area increases with load because more asperities are crushed, thus increasing the contact surface.
Figure 3-8 Machined Surface
3.6
Wear
Wear is the undesirable removal of solids from a sliding or rolling component. There are many kinds of wear. In analyzing a wear problem in a machine, it is necessary to determine the kind of wear that occurred. Analysis requires microscopic examination of the worn area and a close look at the used lubricant. Wear is generally proportional to the applied load and the amount of sliding. 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 the minimum wear expected under BL conditions.
–
Severe adhesion — the removal of metal due to tearing, breaking, and melting of metallic junctions. 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, sand particles between contact surfaces, or hard asperities on an opposing surface). Hard coatings can reduce abrasive wear.
•
Erosive Wear — the cutting of furrows on a surface by hard particles contained in a fluid traveling 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 chemical reaction 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).
3-6
EPRI Licensed Material Lubrication, Friction, and Wear
•
Contact Fatigue — the cracking, pitting, and spalling of a surface in sequence due to cyclic stresses 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 the rubbing off of rust.
•
Fretting Corrosion — the removal of metal oxides from a surface due to a reciprocating sliding motion of extremely low amplitude generated by vibration.
•
Electro-Corrosive Wear — the removal of metal by dissolution in a corrosive liquid with the aid of electric currents. One source of currents is streaming potential from high velocity fluids. The oil serves as the electrolyte.
•
Fretting Wear — localized wear of lubricated surfaces due to reciprocating sliding of extremely low amplitude because of vibration.
•
Electrical Discharge Wear — the removal of molten metal from surfaces due to electrical sparks between them. High static voltages are sometimes generated by large rotating machinery and these are relieved by sparking to regions of lower potential.
•
Cavitation Damage — the removal of material due to cracking and pitting caused by highenergy implosions of vacuous cavities in a cavitating liquid. Liquids cavitate when suddenly subjected to low pressures.
•
False Brinelling — localized wear in lubricated rolling element bearings due to slight rocking motion of rollers against raceways. Wear depressions match the position of the rolling element.
3-7
EPRI Licensed Material
4 APPLICATION PROBLEMS
4.1
Compatibility of Mixed Products
Lubricants can be incompatible with one another on mixing and can potentially cause degradation of properties and performance. Solid formation with oil mixtures can take place because of additive interaction or solubility difficulties. With greases, the usual result of incompatibility is breakdown of the grease gel structure to produce softness. Both of these effects can be undesirable in lubricant applications. Incompatibility can be avoided by not mixing products. Procedures should be set up to eliminate unwanted mixing. When a change to a new product is dictated, careful cleanup should be employed to keep less than about 5% of the old material in the new. Remember, don't mix! If you inadvertently do, you face incompatibility risks. 4.1.1 Oils Lube oils are mostly compatible and miscible with one another in all proportions. A notable exception is mixing a product that contains a chemically acidic additive, for example a turbine oil, with a product that contains a basic additive, for example an engine oil. One will neutralize the other in the presence of moisture and frequently cause a precipitate to form. Precipitates can plug filters and/or other oil passages and cause oil starvation and equipment failure. If you don't know the chemical makeup of the particular products you have, your lubricant supplier can give guidance on this point so you can avoid the acid/base concern. (Anyhow, mixing of lubricants should 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 by the reactants. Precipitates are generally no problem (grease is already semi-solid). Gelling agent interaction 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 in Figure 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 a given set denotes compatibility (“C”) in the table. This change is measured by deviation from the straight line between the two 100% points. Softening is the most likely result of incompatibility, 4-1
EPRI Licensed Material Application Problems
although hardening can take place (< 10% of the cases). Softening is of little concern in a contained system, such as a Limitorque gearbox (unless leakage is rampant). It is only the stayin-place function that is affected – the lubrication function is largely handled by the oil component and its soluble additives. A problem does occur if the grease flows away from the part being lubricated. Rolling element bearings are vulnerable here although they have quite a tolerance for changes in grease consistency. This tolerance runs from about 200 to about 400 in worked penetration. However, the departure from around the 280 norm might cause some increase in required maintenance.
Aluminum Complex
I
Calcium Sulfonate Complex (Calcium Carbonate/ Sulfonate – CCS)
Sodium Soap
Polyurea
Lithium Complex
Lithium 12Hydroxystearate
Lithium Soap
Inorganic (Clay)
Calcium Complex
Calcium 12Hydroxystearate
Calcium Soap
Barium Soap
Aluminum Complex
Table 4-1 Compatibility of Greases
I
C
I
I
I
I
C
I
NA
I
I
C
I
I
I
I
I
I
NA
B
C
I
C
C
B
C
I
C
NA
B
C
C
C
C
I
NA
NA
I
I
I
C
C
NA
C
I
I
I
I
B
I
C
C
I
C
C
C
I
NA
C
I
NA
C
C
I
Barium Soap
I
Calcium Soap
I
I
Calcium 12Hydroxystearate
C
C
C
Calcium Complex
I
I
I
B
Inorganic (Clay)
I
I
C
C
I
Lithium Soap
I
I
C
C
I
I
Lithium 12Hydroxystearate
I
I
B
C
I
I
C
Lithium Complex
C
I
C
C
C
I
C
C
Polyurea
I
I
I
I
C
I
I
I
I
Sodium Soap
NA
NA
C
NA
NA
B
C
NA
NA
C
Calcium Sulfonate Complex (Calcium Carbonate/Sulfonate – CCS)
I
B
NA
NA
C
I
C
C
C
I
I I
*Incompatiblity is defined as a change exceeding 30 points (1 point = 0.1mm) in ASTM worked penetration in more than one of 25/50/75% blends. B = Borderline Compatibility, C = Compatible , I = Incompatible, NA = Not Available.
4-2
EPRI Licensed Material Application Problems
As with oils, different greases should not be mixed. The data cited in the table should be considered generic in nature. A “C” in Table 4-1 is not an endorsement to allow mixing because different grease formulations might give different data. With inadvertent mixing, compatibility risks 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 must be run.
Figure 4-1 Compatibility of Mixtures of Greases With Different Gelling Agents
Compatibility test results will sometimes vary with the method used. Table 4-2 lists some of these methods. High temperatures in the storage (aging) phase are employed to provide test acceleration and assure that any incompatibility will be picked up. A consideration here is not to exceed the heat stability of the individual mixture components. The more severe mix procedures are undertaken to assure thorough mixing. The method we prefer involves 25/75, 50/50, and 75/25 mixtures (10/90 and 9/10 are sometimes also used) of two components stirred with a hand-held electric mixer before aging at 250°F (121°C) for 72 hours. The starting materials get the same treatment. Then, after cooling to room temperature, 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 treated samples. ASTM has now developed the compatibility test listed in Table 4-2. It is more complex and, therefore, three times as expensive to run as the method just cited. Its interpretation is also much more restrictive.
4-3
EPRI Licensed Material Application Problems Table 4-2 Grease Compatibility Tests Group
1 2
Mix
Storage (Aging) Time
Temp
Difference in P
60 1
to Fail
Rock Island Arsenal
Hand Mix + 10,000 1 P
0
70°F (21°C)
±10
Meyers
Hand Mix
72 hr.
250°F (121°C)
±30 for > one mixture
Mobil
RIV Tester
2 hr.
200°F (93°C)
0 - 30 (Compatible) 31- 60 (Borderline) 61+ (Incompatible)
Bolt & Associates
Motor Stirrer
72 hr.
250°F (121°C)
±30 for > one mixture
ASTM D 6185
P
248°F (120°C)
70 hr.
167°F (75°C)
1400 hr.
> about 11 above the value for the thickest component or 11 below that of the thinnest component
100,000 1
2
ASTM 60-stroke or 10,000- or 100,000- stroke worked penetration Applies to low dropping point greases.
4.2
Shelf Life
In general, lubricants are very stable when exposed to the mild conditions encountered in storage or “on the shelf.” Storage life of many years should result. This assumes, of course, no exposure to rain, sunlight, or sources of heat such as adjacent steam lines. Why then do suppliers often limit recommended shelf life to some two to three years? For several reasons: •
Formulations change from time to time for supply and performance reasons – base oil changes, additive changes, and so on. Incompatibility between old and new versions sometimes is a problem. Storage life restrictions limit the supplier's responsibility for old formulations.
•
Conditions of storage can vary widely and some deterioration can take place under situations over which the supplier has no control. For example : –
•
With greases, some cosmetic (but mostly nonfunctional) changes can take place. These relate to the problems described in Section 4.4, “Continuous Versus Intermittent Use.” For example: –
4-4
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 of solution and perhaps not re-dissolve upon return to normal ambient temperature. Such an event would be rare.
Age hardening, that is, hardening during the first few months of life. This occurs mostly with soft greases – consistency generally recovers on working.
EPRI Licensed Material Application Problems
–
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 viscosity oils. A small amount of bleeding is acceptable. (See ASTM D 1742 for perspective.)
Suppliers' reluctance to sanction extended shelf life is understandable. Although lubricant changes in storage are mostly cosmetic, they can be sources of many complaints. However, attention to storage conditions (including those for drums), for example, avoidance of temperature and other environmental extremes, will eliminate virtually all the potential problems. 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 give confidence that stored material is still acceptable. Storage of the drums should be indoors if possible. 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 which change-out is necessary). The vertical scale is logarithmic and gives lubricant life in hours. The horizontal scale is the inverse of absolute temperature. The slope of the band represents an approximate doubling of life for every 10°C (18°F) temperature decrease. One expects this for chemical reactions. The band is used to illustrate that the change might be more or less, depending on the chemical make-up of the lubricant. Also, the best performing lubricants will be on the right side of the band and the poorest performing lubricants on the left. Note that the whole band moves to the right in a parallel fashion as less stress is involved. The band moves to the left if there is more stress.
4-5
EPRI Licensed Material Application Problems
Figure 4-2 Time/Temperature/Irradiation Interplay Continuous Operation in Air of High Quality Lubricant Under Stress
As an illustration, suppose a piece of equipment must be relubricated every 36 months in an application at 93°C (200°F) (A). Then at 104°C (220°F), the relubrication interval would decrease to 18 months (B). At 121°C (250°F), the required interval would be 9 months (C). It would be somewhat more than this (C') or less (C"), as the temperature effect is smaller or greater within the band, depending on the lubricant. Note that at 66°C (150°F) lubricant life would be extended and off the chart at 300 months! Of course, lubricant life cannot be extended indefinitely – 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, at 93°C (200°F) the best lubricant under stress would last about 45,000 hours (D), the poorest lubricant, about one-tenth as long (E). More stress would move the band to the left and shorten lubricant life. Irradiation is one of these stresses but it takes a lot of radiation – more than 10 7 rads – to shift the band appreciably. The approximate 107 rad level is an irradiation threshold. Below it, most lubricants can tolerate irradiation. Appreciably above it, the life of most lubricants is increasingly at risk (see Section 2). Similar temperature thresholds also exist for many lubricants. Up to a certain level, thermal 4-6
EPRI Licensed Material Application Problems
effects are relatively minor but, above that threshold, the thermal component of total stress can become increasingly large. This is tied in, of course, to the approximate doubling of chemical reaction rate by each increase of 10°C (18°F) in temperature. If the rate is very low, a doubling doesn't do much. When the reaction rate is appreciable, doubling has a discernible effect. The threshold is where this rate becomes apparent. Note that temperature and radiation dose thresholds are shown for various lubricants in Appendix A. Oxidation is not addressed specifically in the figure except as an increased stress that would shift the band to the left. However, the lubricant life shown is for products exposed in the presence of air. This is a normal condition and only abnormal exposure conditions, for example bubbling air through 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 stable conditions, as when a grease lubricates a motor bearing. The life of that grease, or of the greased bearing, can be estimated from prior experience or, more generally, from a knowledge of lubrication practice. Often such bearings can run continuously for years. Sometimes, the lubricant must be replenished at prescribed intervals. Now and then, the bearing must be replaced when it becomes noisy or shows other distress. In other situations, a piece of equipment might be on stand-by status until a specified event occurs. 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 under load) can create wear debris from unusual slippage, even with proper lubrication. A spinning bearing 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 dry out. Then, too, stationary bearings are vulnerable to vibrations that can shorten bearing life due to fretting or false brinelling (see Section 3.6). Thus, extended periods of inactivity are not good for long-term performance. Care must be taken to “exercise” the lubricated equipment occasionally. When radiation is involved during lubrication, one would expect frequent operation to be more damaging to the lubricant than intermittent operation. This is because more exposure to oxygen in the air is involved during agitation and oxidation is accelerated by irradiation. However, this does 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, grease drying, or wear fragments in the lubricant.
• Periodic “exercise” to assure that it functions properly without distress. This also maintains adequate distribution of grease to lubricated parts. 4-7
EPRI Licensed Material Application Problems
• Periodic lubricant changes based on experience. Lacking experience, change should be based on intervals established in similar applications. In some instances, lubricant changeout periods are specified by the equipment supplier .
4-8
EPRI Licensed Material
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 use in addressing a concern. The full complement of lubricant tests is very broad in its scope and complexity 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. Samples should be taken as follows and handled carefully: •
When the system is stabilized, neither just before nor just after makeup lubricant has been added.
•
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, be aware that sampling from the bottom of sumps, where dense materials (for example, water and 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 can change by a consistency grade or two and the machinery being lubricated will continue to operate smoothly. However, an off-grade or contaminated product can hasten equipment distress, which might be manifested by: 5-1
EPRI Licensed Material Tests and Analyses
•
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 the information 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 simple on-site sensory examination. A lot can be learned from looking at, feeling, and smelling the used lubricant. 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 the simple ones first! Table 5-1 Sequence of Lubricant Testing Test Type
Description
Sensory 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 and reproducibility.
Analytical Tests
Laboratory; Not always standard - compare to known product. Skill of technician 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 best sample containers for the sensory observations are 4-ounce stoppered glass bottles for oils and 2ounce capped bottles for the greases. The stoppers/caps confine and concentrate odors for detection. All the tests should be done at the same time that similar observations are being made on a known, fresh, “good” product. Sensory tests include the following: 5-2
EPRI Licensed Material Tests and Analyses
•
Appearance: Look at the sample, as shown in Figure 5-1. Is the oil clear and bright? Or is it hazy and cloudy, indicating the presence of water? Is it foamy? Or does it show suspended matter? When examining grease, smear a small amount on a piece of white paper with a knife or spatula. Examine the sample for lumps and other particles, and don't forget the comparison with the fresh, unused sample.
•
Color: Compare with that of the original product. This observation is sometimes useful with light-colored materials. Darkening can indicate oxidation and/or exposure to high temperatures. Remember that color can change by just adding the new lubricant to the system being lubricated!
Figure 5-1 Observing the Appearance
•
Odor: (Figure 5-2) Again, compare with that of the original product. Oxidized oils and greases eventually acquire an acidic, pungent, or “burned” smell. This occurs also at a radiation dose of about 100 megarads. The strong odor of some additives might for a time mask the developing pungent smell.
•
Feel: Oils should feel slippery; greases should feel buttery, not stringy or lumpy. Neither should feel gritty, as from wear debris.
Figure 5-2 Detecting the Odor
5-3
EPRI Licensed Material Tests and Analyses
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 grading systems for oils are given in Appendix B. Oil viscosity is generally specified by the equipment builder for operating machinery. If the viscosity is too high (thick), performance can be sluggish because of increased drag. This also can cause increased temperature, which has an adverse effect on lubricants and sometimes machine life. If viscosity is too low, the oil film might not be able to keep the moving parts separated. In the absence of an antiwear or antiscuff 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 that rotating 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 material through sensory-like tests – sight and feel. If this is not accurate enough for the required purpose, a viscosity gage, shown in Figure 5-3, can be used. This works on the principle that the rate a ball falls in a column of oil depends on the viscosity of the oil.
Figure 5-3 Viscosity 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 tube containing a known oil and a like sphere is used for the comparison. After the two oils are allowed to reach equal temperatures and each ball the same starting point, the instrument is inclined at a slight angle. This starts the spheres rolling. The inclination is stopped when either oil's sphere reaches a calibration point. Then the position of the lagging ball in either tube shows directly the viscosity of the unknown. Both high and low viscosity oils can be used 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 of its thickness. It can be estimated in a sensory-like examination, too. Just collect a series of greases 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 easy to spot the known that matches the unknown.
•
Water “Crackle” Test: This test might be appropriate when considerable amounts of water are suspected in the oil. A metal plate is heated to at least 120°C (250°F) and a few drops of oil are added (be careful, sometimes it spatters). If the oil crackles and pops, it suggests water in excess of 0.1-0.2%. If it simply spreads and smokes, then water concentration is low.
5-4
EPRI Licensed Material Tests and Analyses
•
Blotter Spot Test: This is most useful when a series is conducted over a period of time. To do this test, a drop or two of a representative oil sample is put on a piece of blotter paper. It is important that the paper be placed so that the wetted area does not rest on a supporting surface. After it reaches equilibrium, examine the oil spot, which might look like one of those in Figure 5-4.
Figure 5-4 Sample 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 been overwhelmed 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 is important to know the nature and source of solid debris in the lubricating oil. Such debris can be 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 volatile petroleum solvent from a squeeze bottle (be aware of the fire hazard from the volatile material). After drying, a magnet can separate iron-derived matter from the rest. Examination with 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 to the 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 5-5
EPRI Licensed Material Tests and Analyses
D 217 or D 1403 for grease measurements. The grease apparatus involves dropping a standard cone into a standard cup of grease. The depth of penetration is the measure of consistency, expressed in 0.1 millimeters. The NLGI has classified greases in grades 000 to 6. The grease consistencies versus grade are given in Appendix B. •
Antiscuff and Antiwear: These properties can be measured or studied in a precision laboratory-testing device called the Tribometer or pin-on-disk machine (ASTM G 99). A pin is pressed against a rotating disk. Friction coefficients and wear on the pin and on the disk are measured. Various metal combinations can be used and various test conditions imposed, for example load, speed, surface finish, and temperature. (See Section 6, “Lubricating Motorized Valve Actuators,” Table 6-3, for typical data from the Tribometer.)
•
Infrared Spectroscopy (IR): In this lab procedure, a beam of infrared light is passed through or bounced off a thin film of an organic material, for example a lubricant. The various chemical functional groups within the organic molecule absorb the light at characteristic wave lengths. Thus, one chemical group is distinguishable from another in the IR trace. The absorption peak heights relate to the quantity of species present. Table 5-2 shows the IR peak regions of interest. Table 5-2 IR Peak Regions of Interest Functional Group
Wave Number, cm
Hydrocarbon Base Oil
680-775 1300-1500 2800-3050
EP/Antiwear Agents
900-1000
Soap Grease Gelling Agents
1425-1650
Ester Synthetic Base Oils
1720-1730
Oxidation Products, Rust Inhibitors
1720-1730 3250-3450
Phenolic Oxidation Inhibitors
3600-3660
-1
Note that there are several base oil peak regions. Additives, if their peaks coincide with these, are masked effectively. Hence the term, “dead band regions.” One uses peaks outside the base oil areas for functional group identification and quantitative work. Even when an additive peak barely shows up in the full IR spectrum, it can be magnified by modern Fourier Transform IR using interferometers and computer enhancement for further identification. If a sample of an additive in a product can be obtained (the lubricant supplier can provide a sample), concentrations of it in a base oil or grease can be determined for quantitative IR analysis. Comparison of the known additive peak height with those of the unknown will establish the additive concentration in the latter. The most common approach in using IR is to compare the spectrum of a used lubricant with that of fresh product. It is particularly useful to place both the spectra of the fresh and the used product on the same trace. This makes comparison much easier. The spectra are studied to identify the reasons for the differences, if any, and how they came about in the lubrication process, for example contamination, oxidation, thermal degradation, and so on. Incoming 5-6
EPRI Licensed Material Tests and Analyses
fresh products and materials from storage can be studied in this same way to determine their authenticity and condition. See examples of these spectra in NMAC Lube Notes, October 1999. On page 2, an example of comparing incoming lubricants is shown. On page 5, there is an example of monitoring the depletion of an oxidation inhibitor in a turbine oil. •
Emission Spectroscopy: Spectro Analysis or “Spectro” involves subjecting a lubricant sample to a high-energy spark, plasma, or flame. This treatment excites certain elements in the sample and they emit or absorb light at characteristic wavelengths. Study of the resulting spectra tells what metals are present. Major changes in the elements versus those in fresh lubricant can indicate trouble from wear or contamination from other lubricants, dirt, and so on. Spectro works best with oils. It can be applied to greases, as well, but their semi-solid nature can yield poorer results. Accuracy can be improved by digesting or ashing the oil or grease sample and taking it up into solution. The test is then run on the solution. However, this complicates the method and sharply increases its cost. One widely used, routine emission spectro method yields values for some 20 metals in one shot. It involves a rotating electrode (Rotrode) that dips into the sample and carries it into a high-energy spark area for “burning.” This can handle particles in an oil up to about 10 microns in size. Another routine method with similar capabilities introduces the sample or a dilution of it into an argon plasma (ICP). Higher energy or temperature is involved and the method lends itself well to automation. 9 Routine spectro does not “see” particles larger than 10 microns . Large metal particles from scuffing are missed. One has to use the more complex “total” metals or digestion method of analysis to see all of the particles. Spectro analysis gives no indication of compounds of which the elements are a part. For example, iron in spectro can be metallic but also iron oxide, hydrated iron oxide (rust), iron sulfide, iron phosphate, and so on. The same is true of metal organic species. Atomic absorption is another method; however, it is not widely used in production analytical laboratories. X ray diffraction is the primary analytical method for the identification of crystalline compounds. Table 5-3 identifies sources of metals found in lubricants.
9
Rotrode Filter Spectroscopy is a development that extends the particle size detection capabilities to approach those of ferrography.
5-7
EPRI Licensed Material Tests and Analyses Table 5-3 Sources of Metals in Lubricants Source
•
Metals
Dirt
Al, Ca, Mg, K, Na, Si
Rust
Fe (When water is present)
Grease
Al, Ba, Ca, Li, Pb, Na, Si + Dirt elements (Clay)
Additives
B, Ca, Mg, Ba, Mo, P ,K, Zn, Sb
Wear of bearings, gears
Co, Cu, Sn, Zn, Mn, Fe, Cr, Ni, P
Ferrography: Figure 5-5 illustrates the importance of wear particle size and quantity in determining the condition of operating equipment. Note that we need to get at particles above the normal 10-micron size detectable with routine emission spectroscopy. This can be done through the use of ferrography (or by the digestion method). Note too, in Figure 5-5, that some particle sizes (less than 10 microns) in benign wear also involve some of those in the other failure modes. So, a rapid rise in particles less than 10 microns can be indicative of a wear problem.
Figure 5-5 Wear Particle Size/Concentration and Machine Condition
The ferrograph magnetically separates materials, particularly ferrous metals, from wear, contamination, etc. by size and quantity to reveal their source. Its effectiveness in picking up the larger particles missed in routine emission spectroscopy is shown in Figure 5-6. The particle characteristics from ferrography are often sufficiently specific to determine the wear mode that formed the particle within the machine. 5-8
EPRI Licensed Material Tests and Analyses
Figure 5-6 Detection of Wear and Other Particles
Direct Reading Ferrography: With this technique, a diluted oil sample flows through a precipitator tube where a magnetic array separates particles according to size.Larger sizes separate first, smaller ones further down the tube. Light beams pass through the separated, collected particles to provide information on the amount deposited. Analytical Ferrography: This technique involves flowing the diluted oil over a specially prepared microscope slide, tilted to provide a known flow rate. A solvent wash removes the carrier oil and a ferrogram is prepared from the dried residue. This is examined (and photographed) through an optical microscope. Identifiable solids include several types of steel, and, to a lesser extent, associated copper, lead/tin alloys, friction polymers, moly sulfide, silica, fibers, and carbon flakes. Some of the identifiable wear from ferrography and its causes are given in Table 5-4. Table 5-4 Wear and Its Causes Wear
Cause
Mild adhesive
Acceptable low wear rates
Severe adhesive
Scuffing, usually from excessive loads or speeds
Abrasive
Cutting due to hard particles or hard, rough opposing surfaces
Contact fatigue
Wear particles from pitting or spalling due to point or line contact from rolling elements in gears and ball and roller bearings
Corrosive
Corrosive wear products from chemical action of acids or water to produce fine particles
5-9
EPRI Licensed Material Tests and Analyses
Information from the direct reading technique is useful in trending data on the condition of a machine. The more complex analytical ferrogram is effective when more data are needed in anticipated stress situations. Particle Counting The importance of monitoring and controlling the concentration of particle contamination in lubricating oils and hydraulic fluids cannot be overstated. Modern lubrication programs in power generation use such monitoring and control for hydraulic fluids (for example, EHC fluids), turbine oils, pump lubes, compressor lubricants, crankcase oils, gear oils, and fan/motor bearing oils. In recent years, many case studies have shown how substantial improvements in the reliability of these components can be achieved by monitoring and maintaining cleaner fluids. The ISO Solid Contaminant Code (ISO 4406:99) is probably the most widely used method for representing particle counts (number of particles/mL) in lubricating oils and hydraulic fluids. The current standard employs a three-range number system. The first range number corresponds to particles larger than 4 microns, the second range number for particles larger than 6 microns, and the third for particles larger than 14 microns (see Table 5-5). As the range numbers increment up one digit, the associated particle concentration roughly doubles. A typical ISO Code for a turbine oil would be ISO 17/15/12. While there are numerous different methods used to arrive at target cleanliness levels for oils in different applications, most combine the importance of machine reliability with the general contaminant sensitivity of the machine. Organizations such as ASTM, Westinghouse, ABB, and GE have published guidelines on turbine oil cleanliness. Particle counts can be obtained manually using a microscope or by an automatic instrument called a particle counter. There are many different types of automatic particle counters used by oil analysis laboratories. There are also a number of different portable and online particle counters on the market. The performance of these instruments can vary considerably depending on the design and operating principle. Optical particle counters deploying laser or white light are widely used because of their ability to count particles across a wide range of sizes. ISO 11500 and ISO 11171 are published standards related to the use of optical particle counters. Pore blockage type particle counters have a more narrow size range sensitivity. They are popular because of their ability to discriminate between hard particles and other impurities in the oil such as water, sludge, and air bubbles. More than ten different automatic particle counters are available for fluid monitoring purposes.
5-10
EPRI Licensed Material Tests and Analyses Table 5-5 Particle Count Range Numbers Number of Particles per mL More than
Up to and including
Range number (R)
80,000
160,000
24
40,000
80,000
23
20,000
40,000
22
10,000
20,000
21
5,000
10,000
20
2,500
5,000
19
1,300
2,500
18
640
1,300
17
320
640
16
160
320
15
80
160
14
40
80
13
20
40
12
10
20
11
5
10
10
2.5
5
9
1.3
2.5
8
.64
1.3
7
.32
.64
6
.16
.32
5
.08
.16
4
.04
.08
3
.02
.04
2
.01
.02
1
5-11
EPRI Licensed Material Tests and Analyses
5.3.4 Standard Laboratory Tests Over the years ASTM has developed standard test methods for a variety of materials, including oils and greases. Committee D-2 oversees activities on lubricants. To standardize tests, several laboratories perform them then compare notes in a “round robin” approach. Procedural differences are gradually worked out until laboratories can duplicate one another. Once everyone is satisfied, the procedure is considered to be “standardized” and is given a “D” number. A key part of the method development is the statistical analysis of the test results according to repeatability (one operator, one laboratory) and reproducibility (different operators, different laboratories). Important ASTM tests for lubricants with their designations and precision are given in Table 5-6. The numbers given under repeatability and reproducibility columns show the expected tolerance of the test results 95% of the time. Note that results from any laboratory, with even these most carefully developed test methods, are not absolute – they have pluses and minuses attached to them. The ASTM precision values are the most accurate available. Two appropriate ASTM test methods that address this repeatability and precision, relative to power plant maintenance, are: •
ASTM D 4378, “In-Service Monitoring of Mineral Turbine Oil for Steam or Gas Turbine.”
•
ASTM D 6224, “In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment.”
5-12
EPRI Licensed Material Tests and Analyses Table 5-6 Key Tests for Lubricants Property
ASTM Method
Units
Repeatability (Ir)
Reproducibility (IR)
Greases Consistency
D217
0.1 mm
7*
20
D1403
0.1 mm
11
26
D566
°C
7
13
D2265
°C
6*
15*
Oxidation
D942
Psi drop
5*
9*
Bleeding
D1742
Wt. %
10
17
Bearing Life
D3336
Hrs.
NA
NA
Timken EP
D2509
% of Value
23*
59*
Flash Point
D92
°F (°C)
15(8)
30(17)
Pour Point
D97
°F (°C)
5(3)
10(6)
Viscosity
D445
cSt
0.35% mean
0.70% mean
Neut. No.
D664
mgKOH/g
6% mean
30% mean
D2896
mgKOH/g
3 -24 % mean
7 -32 % mean
D2272
Min. to 25 Psi drop
10% mean
20% mean
G99-95A
Friction Coefficient and Wear
+ 10%
Dropping Point
Oils
Oxidation RPVOT
1
2
1
2
Both Oils and Greases Friction and Wear
—
Notes: An asterisk (*) indicates that the values vary with the level of data. NA indicates that data are not available. 1 Fresh oil 2 Used oil
5-13
EPRI Licensed Material Tests and Analyses
5.3.5 Analytical Test Methods An assortment of specific analytical techniques and procedures is available to the laboratory chemist for studying lubricants. These include: •
Gas chromatography (GC)
•
Scanning electron microscopy (SEM) (for wear surfaces)
•
Thermogravimetric analysis (TGA)
•
Differential scanning calorimetry (DSC)
•
Rotating Pressure Vessel Oxidation Test (RPVOT)
•
Remaining Useful Life Evaluation Routine (Ruler™)
•
Thin-layer chromatography
A brief description of the last five methods will be given here. These tests are not always standard and depend on the skill of the operator. Validity and usefulness of the results can be enhanced by direct comparison with results on a known material tested in the same way. TGA is a promising tool for thermally separating certain greases into their component parts, for example:
Highly volatiles Medium volatiles Combustibles Inert & ash
50-150°C 150-650°C 650-750°C Remainder
(122-302°F) (302-1202°F) (1202-1382°F)
This ASTM (E 1131) method uses 10 mg of sample in the balance setup shown in Figure 5-7. The procedure is what might be termed a destructive distillation. A heating cycle is programmed over 25 minutes from 50 to 750°C (122-1382°F), first in nitrogen and then in air. The residue number correlates with the gelling agent content of metal-containing greases (most products). It doesn't work with ashless greases such as polyurea-gelled materials.
5-14
EPRI Licensed Material Tests and Analyses
Figure 5-7 Schematic of TGA Setup
DSC is a thermal analysis technique that measures the heat flow associated with certain physical and chemical changes in a lubricant. Of most interest is stability to oxidation, which shows up as the time delay to the onset of the oxidative exothermal reaction. The method uses a few milligrams of the test lubricant in the apparatus shown in Figure 5-8. One copper (catalytic) cell or pan on a sensitive thermocouple contains the lubricant and the other is an empty reference cell on its own thermocouple.
Figure 5-8 Schematic of DSC Apparatus
The apparatus is placed in an oven heated to a set temperature, for example, 200°C (392° F). Oxygen is then passed over the two cells. When the antioxidant in the sample can no longer afford protection, oxidation of the lubricant takes place and is detected by a temperature rise in the cell containing the sample. Results correlate roughly with those from the standard RPVOT (Rotating Pressure Vessel Oxidation Test) method, ASTM D 2272 (see Table 5-5).
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EPRI Licensed Material Tests and Analyses
HP-DSC is a variant of DSC in which the oxidation takes place under 500 psi pressure. This reduces volatilization of the test sample during thermal stress. This ASTM Method (D 5483) is more complex than the atmospheric method and is not needed unless volatile components are involved. RPVOT (ASTM D 2272), formerly RBOT (Rotating Bomb Oxidation Test), measures the oxidation stability of turbine oil and is a principal way to determine the remaining useful life of the oil. Oils deteriorate through oxidation, which, if allowed to go too far, results in deposit formation and ultimate equipment failure. The traditional test for evaluating turbine oil oxidation stability has been the ASTM D 943 test. This test is unworkable for maintenance evaluations of turbine oils in service. For example, some top-of-the-line turbine oils can go over 20,000 hours to reach the end point; over 8,000 hours is common in this top group. Lesser quality “standard” materials go for 3,000-5,000 hours. These are very long times for research and evaluation. The RPVOT overcomes this difficulty. Top oils reach the end point in only 2,000 minutes; second quality materials go for 400-600 minutes. The RPVOT is run at 302°F (150°C) in a stainless steel vessel with water and a copper metal catalyst present. The vessel is pressurized with oxygen to 90 psi (620.5 kPa) at 77°F (25°C) and the end point is to a drop of 25 psi (172.4 kPa) in the oxygen pressure. Good correlations between TOST (ASTM D-943) and RPVOT have been made. For these results and more details, see Note No. 8, NMAC Lube Notes, October 1999. RULER™ is a technique to measure the antioxidant levels in lubricants. The small, hand-held device employs a cyclic voltameter to measure the electrochemically active species in the lubricant (see Figure 5-9).
Figure 5-9 Ruler™ (Remaining Useful Life Evaluation Routine) Instrument
A small sample of lubricant is diluted with a select solvent and a voltage is applied to the solution using a glassy carbon electrode. The resulting current flow depends on the concentration of the active species, that is, antioxidant. Comparison of results with those from fresh lubricant and other samples from the lubricated equipment allows an appraisal of remaining useful life.
5-16
EPRI Licensed Material Tests and Analyses
The choice of solvent in the RULER™ test depends on the oil and additive types. For example, esters are polar materials that are soluble in polar solvents, for example, acetone. Hydrocarbons are not in this category. Also, there are three main types of oxidation inhibitors to consider: •
Aromatic amines
•
Hindered phenols
•
Metallic dithiophosphates
Each type can require modification in technique and/or solvent. A varying voltage (0.0-1.0 volt) is applied to the electrodes in the prepared sample. Current flow between the working and other electrodes at certain potentials is a function of type and concentration of the additives. Current flow changes as electrochemical oxidation of the additives takes place at the working electrode. The current flow creates mounds (rounded peaks) in the current/applied voltage curve. Figure 5-10 illustrates this for three oxidation inhibitors. Note that all three can be picked up by this method at the same time.
Figure 5-10 Example of Three Additives and Voltammeter Response
The heights of the rounded peaks relate to additive concentrations. Values for the fresh lubricant are used as the 100% standard; the values for the solvent/base oil/electrolyte alone serve as the 0% standard. Various in-between points can be arrived at accurately by testing known concentrations of the additives in question in base oil. With careful work, repeatability of +/- 5% is claimed for determining the percentage of remaining antioxidant. For more details, see Note No. 5, NMAC Lube Notes, July 1995.
5-17
EPRI Licensed Material Tests and Analyses
Thin-Layer Chromatography (Herguth Laboratories, Inc.) Chromatography is a technique for separating a sample into its components for study. This separation involves two mutually immiscible phases, one of which is stationary. The latter is sometimes a solid, as in thin-layer chromatography. The stationary phase is attached to a solid support material, for example, a plate. The sample, when dropped or smeared on the coated plate, moves across or through this stationary phase by capillary action and is separated by the differences in the chemical and physical properties of the components. These differences also govern the rate of movement or migration of the individual components. The components emerge or are eluted from the system in the order of their interaction with the stationary phase. This technique is called radial planer chromatography. Separation of components occurs through adsorption or similar processes. The Blotter Spot Test (Section 5.3.2) is a simple version of this chromatography. However, the blotter test relies only on diffusion around an initial spot on blotter or filter paper. There is no special solid phase. Figure 5-11 illustrates radial planer chromatographs of fresh and used gear oils.
Figure 5-11 Chromatographs of Fresh and Used Gear Oils
When thin-layer chromatography is used as an oil analysis tool, various machine/oil combinations will show unique trends during the life of the machine and oil. These trends are indicated by bands or zones of different colors and/or densities of the chromatographs. Even unwanted wear metals and debris can be observed, as can the presence of an incorrect oil used as makeup. 5-18
EPRI Licensed Material Tests and Analyses
Ideally, a reference oil is tested to establish the baseline of fresh, clear new oil. Used oils from the machine are then spotted on the chromatographic substrate at regular, time-based intervals. Changes in the appearance of the bands/zones are a clear indication that something has changed in the machine or oil. A close look at the zones with the unaided eye or, if needed, with a 10power magnifying glass can even be correlated with the ISO Particle Code, water contamination, or wear debris. As with most analytical methods, this method is not a predictor of future performance, but rather is a measurement of the situation at the time of sampling. For more details on this topic, see Note No. 5, NMAC Lube Notes, November 2000.
5.4
Using Test Results
A single test result on a lubricant cannot be considered as definitive, even though it might be on a properly collected sample with a carefully performed procedure. This is because of the inherent variability of any test. The only available statistical appraisal of test precision is for ASTM procedures. That is one of the reasons they are so widely used when standard tests are required. Table 5-5 lists these data for some key procedures. To cite an example, the repeatability of the l/4-scale grease penetration test, D 1403, is listed as 11 points. This means that 95% of the time a result by this procedure will fall within +/- 11 points of the true value. Some 5% of the time the result will fall outside this envelope. So, +/- tolerances are attached to any result. When a result seems outside the acceptable variability band, begin again with a new sample and a new test. If the second result checks the first, it might truly be showing a problem. The cause of this problem should receive attention. If the two results diverge, additional testing is needed to resolve the disparity. Non-standard tests (that is, test methods without an ASTM-type statistical matrix) present a different picture. There, test credibility needs to be established. Replicate tests will determine repeatability, but not reproducibility. However, repeatability data should be enough to allow reliable tests. Merely compare results on an unknown or used lubricant with those for fresh material. Use this approach particularly with shortened or special tests conducted at low cost by many commercial laboratories.
5.5
Trending
Enough cannot be said for having in hand samples of the unused lubricant that was originally charged to a piece of equipment under study. At the least, one should have stored data on tests run on the fresh material when it was introduced. Then, as data are obtained on used material, they can be compared directly with the stored information. Essentially all test procedures profit from such comparisons. A lubricant analysis program should feature periodic sampling and testing. The test data can then be plotted on a continuing graph, as in Figure 5-12 10, to establish a trend. Place test variable limits above and below the trend line. Thus, minor variations will not affect the equipment operation but results outside these limits will be noticeable. If, on resample and retest, the results 10
Footnote refers to q, Appendix A, Section A.2.
5-19
EPRI Licensed Material Tests and Analyses
return to the trend line, all is well. If not, then a problem exists that needs attention. At some point, the trend line will break away and a preset warning limit or flag is up. When this occurs, retest to verify results, then go for changeout, makeup addition, adding inhibitor, etc., and study further if needed. Note the warning limit line in Figure 5-12.
Figure 5-12 Sample Plot of Lubricant Properties
5.6
Warning Limits
Classic warning limits for oils and greases are given in Table 5-7 11. The following discussions about these limits are for clearer understanding. •
Determine which property test limit of the lubricant is the most critical and trend it. For example, for turbine oils this will be oxidation inhibitor content. The inhibitor is sacrificed in protecting the oil (or grease). When its concentration is reduced sharply, oxidation of the lubricant takes place to form acids and eventually polymers that increase viscosity. But acid formation and viscosity increases occur late; a decrease in inhibitor content is an early warning sign or leading indicator of deterioration.
•
Sometimes accelerated performance tests are needed to assess remaining performance properties. For example, DSC or RPVOT (ASTM D 2272) are useful for antioxidation performance. The sacrificed inhibitor might generate oil-soluble species that accelerate lubricant breakdown.
•
The application involving a lubricant also impacts its warning limit. A 50% additive depletion with an oil in a turbine system might mean that years of service still remain for the product. A similar drop in inhibitor content with a reactor cooling pump oil might dictate action soon.
11
Footnote refers to q, Appendix A, Section A.2.
5-20
EPRI Licensed Material Tests and Analyses Table 5-7 1 Typical Warning Limits for Certain Lubricant Services Service Oils
Property
Diesel Engine
Greases Steam/ Gas Turbine
Hydraulic System
Gear
Air Compressor
Bearings, Gears, Actuators
NA
NA
NA
3
Appearance Color/Odor
Unusual Change from Original
Wear Metals Content By Emission/Absorption Spectroscopy
Unusual Change from Original
Calcium Content By Absorption, ASTM D 4626T, ppm, Max.
NA
20
Consistency Viscosity at 40°C (100°F) (ASTM D 445), Change, %.
10-25
10
10
10
10
NA
NA
NA
NA
NA
NA
1 Grade (30 points)
Water Content % Vol. Max. 6 (ASTM D 95)
0.2
0.05-0.2
0.05
0.03-0.1
0.1
NA
Total Acid Number mg KOH/g, Max. (ASTM D 664)
NA
0.3
NA
NA
NA
NA
NA
50
50
NA
NA
NA
EP Additive % of New Lube, Min.
NA
NA
NA
50
50
NA
Rust Test Oil (ASTM D 665)
NA
Fail Test
Fail Test
NA
NA
NA
Base No. mg KOH/g, Min.
>3
NA
NA
NA
NA
NA
Fuel Dilution Vol. %, Max.
3
NA
NA
NA
NA
NA
Max. Penetration (ASTM D 217). NLGI Grade Change, Max.
2
Oxidation Inhibitor % of New Lube, Min. 2
4
NA
3
3
5
3
5
Notes: 1 These warning limits are derived from past experience. No definitive studies have been conducted to ascertain these points. 2 These points can be determined by Infrared analysis. Also, the atomic absorption procedure can be used for EP additives. 3 This is not a sensitive criterion. Other limits should be used for early warning. If original viscosity is known, apply the 10% increase to it to arrive at the warning limit. 4 NA = Not Applicable. 5 Depending on the application. 6 Based on experience and ASTM D 6224 and D 4378.
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EPRI Licensed Material Tests and Analyses
5.7
Cleanup Considerations
A lubricant is changed because the maintenance plan is being followed or because there is a possible problem to resolve. In the latter case, cleanup is essential even if the replacement lubricant is the same type as the old. This is because the old lubricant has either had a problem or been the indicator of a problem. The old lubricant becomes a contaminant in the new lubricant and is best removed, if possible. The principal way to ensure cleanliness in the system being changed is to drain the system, add fresh lubricant, drain again, and repeat until the debris is removed. Sampling and sensory testing, as already discussed, should suffice for determining when flushing is sufficient. This procedure should also be followed when making a change to an updated product. Such a change might take place even though no equipment or lubricant distress has been noted. Greases are more of a problem with cleanup than are oils. The general pattern is to introduce new lubricant and expel old grease at the same time until sufficient old product has emerged. This is generally accomplished with the machine in operation to prevent over-filling. Open rolling element bearings can be handled in this fashion. Double-shielded bearings are another problem and attempts to regrease them may or may not be successful depending on prevailing conditions. For a further discussion of this, see Note No. 1 of the June 1998 NMAC Lube Notes.
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EPRI Licensed Material
6 LUBRICATING MOTORIZED VALVE ACTUATORS
Limitorque valve actuators have four major areas requiring lubrication. Three, if one eliminates the common motor bearings that come lubricated for life. These three areas are: •
Main gear box
•
Limit switch gear box
•
Stem and stem nut
To minimize oil leakage, all of these are lubricated with greases. Selection of grease for the limit switch gearbox is the easiest because it involves mostly brass gears at low load. Selection for the main gearbox with its carbon steel worm against a manganese bronze (Limitorque bronze) worm gear is slightly more difficult. It requires a mild antiscuff (formerly called EP) product. Selection for the stem/stem nut interface is the most difficult because it has a Limitorque bronze nut driving a stainless steel stem, which requires a more effective antiscuff product. Table A-9 in Appendix A, “Limitorque Valve Actuator Lubricants”, details the products in use and some proposed for use for these applications. However, these are not the only products that will work satisfactorily; any product that meets the Limitorque specifications can be used. Table A-11 in Appendix A, “General Purpose Greases,” shows equivalent products. Data are available to justify substitutions. Requirements for the main gearbox include antiscuff properties, bleed resistance, temperature and water stability, compatibility with seal elastomers, and noncorrosivity. Antiscuff ability, along with bleed and heat resistance, are the key properties . As noted in Table A-9, the greases in use are much different in composition. This can create a compatibility problem if the products get mixed. With this in mind and from the viewpoint of product consolidation, it would be preferable to have a single grease to do the job in all three areas of the actuator. This, of course, means that the new product would have to be powerful enough to do the toughest job (stem and stem nut lubrication) and yet be satisfactory for other areas. Thus, it needs to be a low-bleeding-type grease with good antiscuff properties and compatibility with brass. The calcium sulfonate complex greases (CCS - calcium carbonate/sulfonate) have now emerged as the best candidates for this single grease. This possibility of using a single grease was studied under the EPRI MOV Performance Prediction Program (see EPRI report TR-102135). During the course of this study another objective emerged – studying the friction and wear performance of off-the-shelf greases and solid lubricants for the stem/stem nut alone. These two investigations were carried on simultaneously.
6-1
EPRI Licensed Material Lubricating Motorized Valve Actuators
6.1
Stem Nut Friction and Wear – Off-the-Shelf Products
Friction at the stem/stem nut interface is a key factor influencing the conversion of motoroperated valve (MOV) operator torque to valve stem thrust. One of the factors affecting this value is the lubricant employed at this interface. Wear of the stem nut, of course, relates to friction and is an important item in maintenance. Some 13 commercial greases were tested in an SMB-0 actuator, coupled to a globe valve, for about 250 opening and 250 closing strokes (500 strokes). All the products tested were either presently in use or proposed for use. The effects of stroke number and load (0-17,000 lb.) on friction and on wear of the stem nut were determined. A new, premeasured Limitorque bronze nut was employed for each test and it drove a type 410 stainless steel valve stem. The tests were performed at room temperature. Table 6-1 shows the results obtained. Note that eight of the first thirteen listed show friction coefficients of below 0.15 at the beginning of the 500 stroke run (generally the highest point). Six of them exhibit only small variations in friction with stroke. Those greases with the best antiscuff properties showed the lowest wear, for example Mobilux EP, Multifak EP, and so on. There is little correlation between low friction and low wear. The last two lubricants with special additives will be discussed in a later section.
6-2
EPRI Licensed Material Lubricating Motorized Valve Actuators Table 6-1 Friction and Wear Performance Summary (500 Stroke Stem/Stem Nut Lubricant Tests with SMB-0) Lubricants
Coefficient of Friction Under Dynamic Loading @ 10,000 Lbs.
Tooth Wear in Mils
Average COF
COF Beginning of Run
COF End of Run
0.05 in. Above Tooth Root
0.10 in. Above Tooth Root
Moly 101
0.13
0.12
0.13
2
3
1
0.13
0.12
0.14
4
0
0.13
0.13
0.13
1
0
Never-Seez 165
0.14
0.17
0.10
4
4
Fel-Pro (Loctite) N-5000
0.10
0.14
0.08
2
3
0.12
0.19
0.08
3
4
0.12
0.13
0.12
1
2
Multifak EP-1
0.12
0.12
0.12
1
0
Lubriplate 930 AA
0.13
0.15
0.13
1
1
RF Graphite
0.12
0.22
0.09
4
5
Dow Corning 44
0.14
0.18
0.10
1
3
0.09
0.11
0.07
1
1
0.08
0.10
0.07
2
2
2
0.09
0.10
0.07
1
1
2
0.10
0.13
0.08
1
1
1
SRI
Mobilux EP-1 3
Never-Seez 160
3
Dura-Lith EP-1 1
3
Multi-Motive 1 Nebula EP-1
3
3
Darina EP-1 + additives
Shear Magic + additives 1
Also in 2000 stroke runs (see Section 6.4). Additives are polymer tackiness agent and antimony/sulfur/phosphorus antiscuff (EP) agent. 3 Obsolete products. 2
Figure 6-1 is a plot of friction coefficient at 10,000 lb. dynamic closure load versus number of strokes for three typical lubricant types from Table 6-1. A preferred lubricant will have the property of low friction coefficient with little or no change with number of strokes. The data in Table 6-1 show a decrease in friction in many cases as the test progresses. This might be a result of break-in of the stem nut, because each test was started with a new nut. However, this effect was not universal. For example, no change was noticed in Mobilux EP or Multifak EP. 6-3
EPRI Licensed Material Lubricating Motorized Valve Actuators
Figure 6-1 Composite of Friction Coefficient (@10,000 lbs) Versus Number of Strokes
6.2
Stem Nut Friction & Wear – Solid Lubricants and Improved Nut Cutting Procedure
A permanent solid lubricant for the stem/stem nut and a single grease for the other two areas of an MOV is an attractive alternative to a single lubricant for the whole actuator. Very low stem/ stem nut friction could theoretically be obtained through the use of effective solid lubricants. However, one problem with the solids is their poor durability. This prompted a closer look at the quality of the stem nut threads to which the solid lubricants would be applied. Application of solid lubricant to the nut threads was considered to be the only practical approach as the nuts are more frequently and easily replaced than the valve stems. Our examination showed that the stem nut quality is generally poor, irrespective of whether the nut is made at the utility machining facility or at that of the valve vendor. Figure 6-2 illustrates a utility-made new SMB-O nut tooth with a damaged upper area. Scuffing of the surfaces is also prevalent as a result of machining. There are even instances of the threads not being concentric with the outside body of the nut. This would cause the nut to wobble on the stem. This should increase friction and wear. In short, making the threads out of Limitorque bronze is not an easy job and should receive careful attention so that stem nut durability can be improved and friction and wear reduced.
6-4
EPRI Licensed Material Lubricating Motorized Valve Actuators
Figure 6-2 Cross-Section of Macrograph of New SMB-O Stem Nut Thread – Standard Machining
An improved thread cutting procedure was developed for both SMB-O and -000 nuts. This involved starting with standard Limitorque drilled blanks and using a high quality lathe. (It was assumed that such a lathe would be available at any utility maintenance facility.) A special floating tap holder was used to avoid non-concentric boring and tapping. A reamer and three taps were used to cut the threads – a rougher, semi-finisher, and a finisher. Using this method, large cuts that can yield thread damage are avoided. To determine the optimum production of high quality threads, cutting fluids and methods of application were investigated. This new procedure was used to make all of the nuts for the 500-stroke actuator test program. The following solid lubricants were applied to separate stem nuts and then run in the actuator: • • • • • •
Sputtered Molybdenum Disulfide Bonded Molybdenum Disulfide -1 Bonded Molybdenum Disulfide - 2 Plated Paladium Silver/Indium Graphite Insert Graphite/Resin in Solvent
All of these solid lubricants failed after only a few strokes, exhibiting very high friction and wear. The graphite insert was graphite/resin cast into the thread form and fitted into a drilled out Limitorque bronze nut. It failed quickly due to lack of mechanical strength under load. Thus, the promise of solid lubricants for the stem nut application did not materialize in practice.
6-5
EPRI Licensed Material Lubricating Motorized Valve Actuators
6.3
Search for Improved Actuator Lubricants
There are two important grease performance elements for Limitorque actuators – bleeding and antiscuff properties. Low bleeding relates to reduced leakage through seals and high load carrying capacity to the ability to handle the tough stem/stem nut lubrication task. Bleeding tests and tests with the pin-on-disk machine were used to study these properties. Table 6-2 shows the results of the bleeding tests. There are large differences between various grease types in bleeding tendencies. The first three types listed, being the lowest in bleeding, were chosen for further study. Small amounts of tackiness agents (polymers) are effective in lowering bleeding.
Table 6-2 Bleeding Tests¹ on Grade 1 Greases (including effects of gelling agents) Gelling Agent Calcium Complex
2
3-8 2,3
Calcium Sulfonate Complex (CCS - Ca Carbonate/Sulfonate) 2
Clay
10 mg KOH/g) Products are made from premium base oils plus additives to provide detergency and resistance to wear, corrosion, oxidation, and foaming. Typically, products have high base reserve to accommodate high sulfur fuels (>0.5% sulfur). Another group will accommodate low sulfur fuels. Many oils (no zinc) are compatible with silverlined sleeve bearings.
Crankcases of auxiliary Diesel engines — railroad/marine type — used for emergency power.
• • • • • • • •
BP Energol REO Chevron Diesel Engine Oils Delo 6170 CFO, Marine 1000 Exxon Diol 13D, 17D Lyondell Gascon Supreme Plus Mobil Mobilgard 450 NC Pennzoil RR513, RR517 Shell Caprinus XR Texaco Diesel Engine
Low Base Reserve (TBN 7-9) Products recommended for modern low sulfur diesel fuel (see Lube Note No. 4, July 1996). Most oils contain zinc additives and likely will not be compatible with silver-lined bearings in EMD engines. However, such silver bearings should be phased out by 2006. Also, silver bearings can be retrofitted with bronze (at a cost). Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-2
• • • • • • •
Chevron Marine Engine Oil Delo 194 (no zinc), Delo 100, Delo 400 Exxon XD-3 Extra Mobil Delvac Pennzoil Long Life Heavy Duty Engine Oil Phillips Super HD II Motor Oil Shell Rotella T Texaco Ursa Premium TDX
EPRI Licensed Material Appendix A Table A-3 Low-Pressure Hydraulic Oil ISO Viscosity Grades 32, 46, 68, 100 Operating Limit Range Profile
Products are made from refined mineral oils plus oxidation and corrosion inhibitors, antiwear/antiscuff agents, and foam suppressants. They contain lower levels of additives than in high-pressure hydraulic oil.
e
Application • • •
•
Moderate duty hydraulic systems general machinery Reciprocating air compressors Circulating systems and bearings (plain and rolling element) where loads and temperatures are moderate Reduction gears, speed reducers, and high speed spindles at moderate loads
Products • • • •
• • • •
BP AW Castrol Hyspin AW Chevron Machine AW Conoco Hydroclear Multipurpose R&O Exxon Humble Hydraulic H Lyondell Duro; Polarvis Mobil Hydraulic ISO Texaco AW Hydraulic
b
c
Temperature °C (°F)
Radiation Rads
65-105 (150-220)
107-5x107
Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-3
EPRI Licensed Material Appendix A Table A-4 e High-Pressure Hydraulic Oil ISO Viscosity Grades 32, 46, 68, 100 Operating Limit Range Profile
Products are made from refined mineral oils plus oxidation and corrosion inhibitors, antiwear/antiscuff agents, and foam suppressants.
Application •
• •
Vane, gear, and piston-type pumps operating in heavyduty hydraulic systems above 1000 psi. Operating temperatures are above those typical of low-pressure systems. Hydraulically activated equipment. Machine tools and presses.
Products • • •
• • • • • • •
BP Energol HLPHM Castrol Paradine AW, Tribol 943AW Chevron Hydraulic AW, ECO Hydraulic AW, Rykon Premium Conoco Hydroclear AW Exxon Nuto H Lyondell Duro AW Mobil DTE 10M, 20 series; SHCd 500 series Pennzoil Pennzbell AW Shell Tellus Texaco Rando HD, HDZ
Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-4
b
c
Temperature °C (°F)
Radiation Rads
70-115 (160-240)
5x107-108
EPRI Licensed Material Appendix A Table A-5 Compressor Oils Operating Limit Range Profile
Premium quality multipurpose industrial oils made from specially refined mineral oils; can contain antioxidant, antiscuff agent, alkalinity, rust inhibitor, metal deactivator, foam suppressant, and/or mist control agent.
Application • • • • •
Reciprocating and rotary air compressors Mild duty industrial gear sets Oil mist systems Hydraulic systems Multi-stage compressors
Products • •
•
• • • • • • •
BP Turbinol – T Castrol Reciprocating Compressor Oil, Tribol 1750d Chevron Compressor Oil 260 R&O, Machine R&O LVI Conoco HydroclearDiamond Class Exxon Exxcolub 77 Lyondell Compressor 7585 Mobil Rarus 427, 800d series; SHC d 1024, 1026 Pennzoil Pennzcom Shell Corena S Texaco Cetus DEd, d Cetus PAO
b
Temperature °C (°F)
Radiation Rads
71-115 (160-240)
10 -5x10
7
c
7
Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-5
EPRI Licensed Material Appendix A Table A-6 High Load Extreme Pressure (EP) Gear Lubricants Operating Limit Range Profile
Products are made from highly refined mineral oils plus sulfurphosphorus antiscuff (EP) agents. They can also contain antiwear agents, antioxidants, corrosion inhibitors, and foam suppressants. These lubes are lead-free.
Application • •
• • •
• • •
Enclosed gear systems Chain drives, sprockets, bearings, and couplings High horsepower gear drives and reducers Spur, bevel, and worm gears Hypoid gears at moderate temperatures, loads, and speeds Worm drive axles Heavy, suddenly (shock)-loaded equipment Applications where AGMA specifies an “extreme pressure” (antiscuff) lubricant
Products • • • • • • • • • •
BP Energol - GR - XP Castrol EP Gear Lubricant; Alpha Gear, Tribol 1100 Chevron Gear Compound EP Conoco Hydroclear EP Exxon Spartan EP; Spartan Synthetic EPd Lyondell Pennant NL Mobil Mobil Gear 600 series; SHCd series Pennzoil Super Maxol EP Shell Omala Texaco Meropa
Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-6
Temperature °C (°F)
b
Radiationc Rads
60-95 (140-200)
107-108
EPRI Licensed Material Appendix A Table A-7 Open Gear Lubricants Operating Limit Range Profile
Products are high viscosity mineral oils, sometimes gelled to give black, tacky greases. Generally they contain special fillers such as molybdenum sulfide and/or graphite. They also contain rust inhibitors and wetting agents. Products are stringy.
Application •
•
•
Antiscuff (extreme pressure) film for slowly moving parts. Industrial equipment such as slow moving, heavily loaded gears, hoists, and cranes. Wire rope
Products
b
c
Temperature °C (°F)
Radiation Rads
65-120i i (150-250 )
5x10 -2x10
Lithium soap-gelled • • • • •
Conoco Tacna M 5 Exxon Dynagear, Dynagear Extra Mobil Mobilux EP III Shell Retinax AM Texaco Molytex EP
Calcium ComplexGelled • •
7
8
Chevron Open Gear Grease; NC; h Aerosol j Texaco Texclad 2
Ungelled • • • • •
Castrol Open Gear 800, Molub-Alloy 936 SF Open Gear Chevron Mill Lubricants Exxon Suretth h Mobil Mobiltac Series Pennzoil Open Gear and Wire Rope Spray
Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-7
EPRI Licensed Material Appendix A Table A-8 Antiseizure Compounds Profile Products are typically dispersions of solids in a petroleum carrier. Solids can be graphite, molybdenum sulfide, copper, or nickel flakes. Products are usually specific to an application and are NOT interchangeable or compatible. Usually applied by spray or brush.
Application • • • • •
Threads Keyways Valve components Studs and bolts Cable and rods
n
Products
Acheson DAG 154 Graphite Lube
Carrier/ Solid* So/G, R
Bostik Never-Seez Regular
Gr/Cu
Nuclear NiGrade
Gr/N
b
Temp. °C (°F)
Radiationc Rads 9
455 (850)
>10
980 (1800)
>10
9
9
Chesterton Nickel Antiseize Compound 772
Gr/N
1430 (2600)
>10
Chevron Tool Joint Compound
Gr/G, Cu
400 (750)
>10
1000
Gr/G, Cu
1150 (2100)
>10
G-N
Gr/G, M
400 (750)
>10
Molykote P37
Gr/G, Zr
1400 (2550)
>10
Neolube No. 1, 2
So/G, R
200 (400)
>10
Neolube No. 650
Gr/G
635 (1200)
>10
Jet Lube SS-30
Gr/Cu, R
980 (1800)
>10
N1000
O/G, Cu
980 (1800)
>10
N5000
O/G, N
1430 (2600)
>10
N7000
Gr/G
464 (850)
>10
550 Moly
Gr/G, M
400 (750)
>10
Nikal
Gr/N, R
1430 (2600)
>10
Nuclear NonMetallic
Gr/G
1315 (2400)
>10
Texaco Thread Compound
Gr/Cu
980 (1800)
>10
Zinc
Gr/Z
350 (660)
>10
9
Dow Corning 9 9 9
Huron
*Key for Carrier/Solid Carrier: SO = Solvent GR = Grease O = Oil Solid: G = Graphite M = MoS2 Cu = Copper N = Nickel R = Resin Z = Zinc, Zinc Oxide Zr = Zerconium Dioxide A = Aluminum
9 9
Loctite
Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-8
9
9 9 9 9 9 9
9
9
EPRI Licensed Material Appendix A Table A-9 Limitorque Valve Actuator Lubricants Operating Limit Range Profile
Calcium sulfonate complex (CCS) gelled grease (see Table A11).
Application
Main gear case
Products
b
k
Temp. °C (°F)
Radiation Rads 7
8
7
8
7
8
7
8
Cor-Tek MOV Plus, Long Life
95-150 (200-300)
5x10 -3x10
Calcium complex-gelled mineral oil plus additives for wide range of load, speed, temperature, and moisture conditions.
Exxon Nebula EP-0* Exxon Nebula EP-1*
95-150 (200-300)
5x10 -2x10
Lithium complex-gelled (see Table A-11).
Mobilith AW
95-150 (200-300)
5x10 -2x10
Cor-Tek MOV Plus, Long Life
95-150 (200-300)
5x10 -3x10
l
95-120 (200-250)
10 -2x10
95-163 (200-325)
10 -5x10
Calcium sulfonate complex-gelled grease (see Table A-11).
Geared limit switch
Ester-based, lithium soap-gelled product, formulated for use over a wide temperature range.
Exxon Beacon 325
Synthetic hydrocarbonbased, clay-gelled product. Designed for use over a wide temperature range.
Mobil Mobilgrease 28
m
7
8
8
8
Lubricated for motor life, as supplied.
Motor bearings
Long Life Product
NA
NA
Greases, Solid Lubricants
Valve stem/ stem nut
Many with varied success.
NA
NA
c
* Still in use but now being phased out by Exxon NA = Not applicable Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-9
EPRI Licensed Material Appendix A Table A-10 Fire Resistant Hydraulic Fluids Operating Limit Range Profile
Three types are commercially available (the types are NOT interchangeable or compatible)
Application •
Industrial hydraulic and control applications where hazardous conditions require the use of a fireresistant fluid.
Note: DO NOT MIX FLUID TYPES.
Products
b
Temperature °C (°F)
Radiation Rads
c
Water-Glycol • • • • • • •
BP Energol – FRG-46 Castrol Premium Fluid 200 Exxon Firexx HF-C46 Houghto-Safe 400-600 Series Mobil FR 200D Fluid Pennzoil Glycol FR Texaco Hydraulic Safety Fluid
95 (200)
5x107-2x108
80 (180)
5x10 -5x10
80 (180)
5x10 -5x10
95 (200)
10 -10
Water-in-Oil Emulsion • • • • •
Conoco FR Exxon Fyrexx HF-B Lyondell Duro FR-HD Mobil Pyrogard D Pennzoil Maxmul FRP/G
Oil-in-Water Emulsion •
6
7
6
7
Pennzbell HWCF
Phosphate Ester • • • • •
Akzonobel Fyrquel EHC, MTL Forsythe (FMC) Reolube Houghton International Houghto-Safe 1000 Series Mobil Pyrogard 53 Pennzoil Pennzsafe FE
Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-10
6
7
EPRI Licensed Material Appendix A Table A-11 General Purpose Greases—Grades 00, 0, 1, 2, 3 Operating Limit Range Profile Products are made from refined mineral oils plus gelling agent, oxidation and corrosion inhibitors, and antiscuff (EP) agents.
Application Bearings
•
Motor
•
Pump
•
Fan
•
Compressor
•
Couplings
b
Temperature °C (°F)
Products
c
Radiation Rads
Lithium soap-gelled • • • • • • • • • •
BP Energrease-LS-EP Castrol Longtime PD Chevron Dura-Lith EP Conoco EP Conolith Exxon Lidok EP Lyondell Litholine HE-P Mobil Mobilux EP Pennzoil Pennlith Shell Alvania EP g Texaco Multifak EP; Premium RB
7
8
95-135 (200-275)
10 -10
95-150 (200-300)
5x10 -10
95-150 (200-300)
5x10 -10
95-150 (200-300)
5x10 -3x10
120-175 (250-350)
5x10 -3x10
Lithium complex-gelled • • • • • • • • •
BP Energrease LC-EP Castrol Pyroplex Blue, Molub-alloy 860 ES Chevron Ulti-Plex EP; Ulti-Plex d Synthetic EP, RPM Automotive LC EP Conoco Conolith HT Exxon Unirex N Lyondell Litholine Complex EP d Mobil Mobilith AW, SHC 15, 100 Pennzoil Premium Lithium Complex Texaco Starplex
Calcium complex-gelled • Exxon Nebula EP*
7
8
7
8
Calcium sulfonate complex (Calcium carbonate/sulfonate - CSS)-gelled •
Castrol SFG
•
Compton G-2000 Series
•
Cor-Tek MOV Plus, Long Life
•
Petro-Canada Peerless LLG
7
8
7
8
Polyurea-gelled •
Chevron Rykon Premium EPg, g Black Pearl EP; SRI
•
Conoco Polyurea , EP Polyurea
•
Exxon Polyrex EM , EP
•
Shell Dolium BRB
•
Texaco Polystar RB
g
g
g g
* Obsolete product Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-11
EPRI Licensed Material Appendix A Table A-12 Coupling Greases Operating Limit Range Profile
Products are made from high viscosity mineral oils, gelled with a soap and/or a polymer. Most contain antioxidants and antiscuffing (EP) agents. Products are designed to resist separation by centrifugal force.
Application
Products
Couplings
•
•
Chevron Coupling
Flexible
•
•
Geared
Exxon Ronex Extra Duty*
•
High speed
•
Falk LTG
•
High load
•
KOP-FLEX KSG KHP 1
•
Mobil Mobilux EP 111
•
Texaco Coupling
b
66-95 (150-200)
* Below 3600 rpm Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-12
Radiation Rads
Temperature °C (°F)
7
8
10 -10
c
EPRI Licensed Material Appendix A Table A-13 q Grease Types and Performance Dropping Point °C (°F)
Condition After Heating to 200°C (400°F) and Cooling
Max. Temp. for Prolonged Use °C (°F)
Water Effects
Stability of Penetration on Working
Bleeding Tendency
Gelling Agents Calcium r soap
85-150 (185-300)
Oil and soap separate
70-120 (160-250)
Highly resistant
Good to excellent
Medium
Calcium complex
260-300 (500-570)
Hardens; OK after working
120-150 (250-300)
Highly resistant
Excellent
Low
Calcium Sulfonate complex [Calcium carbonate/ sulfonate (CCS)]
300-320 (570-610)
Little change after working
150-175 (300-350)
Highly resistant
Excellent
Low
Lithium s soap
170-200 (340-390)
Little change after working
120-135 (250-275)
Some emulsification t to resistant
Poor to t excellent
High
Lithium complex
260-300 (500-570)
Little change after working
150-175 300-350
Resistant
Excellent
Medium
Polyurea, Polyurea complex
240-260 (465-500)
Little change after working
150-175 (300-350)
Highly resistant
Fair to excellent
Low
Inorganics
260+ (500+)
Little change after working
120-140 (250-285)
Resistant
Fair to excellent
Low
Sodium soap
175-300 (350-570)
Hardens; OK after working
120-150 (250-300)
Emulsifies
Fair
Medium
Barium soap
200-260 (390-500)
Little change after working
120-140 (250-285)
Highly resistant
Good
Low
Aluminum complex
240-270 (465-520)
Slight hardening
110-135 (230-275)
Resistant
Good to excellent
Low
Note: Lettered superscripts refer to “Footnotes” defined in Appendix A, Section A.2.
A-13
EPRI Licensed Material Appendix A
A.2 a
Footnotes
Higher viscosity grades are available in many cases for use as non-EP (antiscuff) gear oils.
b
Quite long life (years) can be expected at the lower value. Life is about halved by each increase of 10°C (18°F) in operating temperature. Oil change-outs should be expected with prolonged use at the upper temperature values. c
Lower value is the point at which no significant change is expected. Lubricant should be replaced at the upper value or its performance watched closely. 1 RAD ≅ 0.01 gray ≅ 100 ergs/g ≅ 0.01 joule/kg ≅ 4.30 x 10-6 btu/lb.
d e
Synthetic base oils. High-pressure hydraulic oils also function satisfactorily in low-pressure systems.
f
Designed for maximum radiation-resistance.
g
Designed primarily for ball and roller bearings. Contains no EP additive.
h
Some contain a nonflammable solvent (often halogenated), usually packaged in aerosol form or in cartridges for ease of application. i
Might be used at higher temperatures in situations where the hydrocarbon carrier is evaporated and the solids remain as the lubricant.
j
Calcium soap-gelled. Temperature limit 80°C (175°F).
k
Do NOT mix products. Acceptable substitutes may be made if they meet or exceed Limitorque lubricant specifications and plant EQ requirements.
l
The ester base oil may soften or swell certain paints and elastomers.
m
Limitorque is not responsible for continued 1E qualification unless motors are returned to Limitorque for repair. If return is not possible, the user assumes this responsibility.
n o p
Not intended as a complete list. Products contain no solids other than gelling agent. Contains graphite and molybdenum sulphide residual lubes.
A-14
EPRI Licensed Material Appendix A q
Taken in part from Chevron Research Bulletin, “Grease” 1976, 1983; “Automotive Engine Oils,” 1989; “Testing Used Engine Oils,” 1983; “Industrial Oil,” 1985. r s t
Includes calcium hydroxystearate-gelled products. Includes lithium hydroxystearate-gelled products. The better products are lithium hydroxystearate-gelled.
u
Many can be used for smaller diesels, too (API CD Classification). Oils exclusively for smaller diesels are many and varied and are beyond the scope of this report.
A-15
EPRI Licensed Material
B APPENDIX B
B.1
Glossary
AGMA
American Gear Manufacturers' Association.
Alkylaromatic
Alkyl (paraffinic) side chain on an aromatic (that is, benzene, naphthalene, and so on) ring.
Antiscuff
Formerly called extreme pressure (EP). Antiscuff additives enhance scuff-resistance of lubes and reduce metal-to-metal contact. This decreases tendency toward seizing and galling.
ASTM
American Society for Testing and Materials.
Atomic Absorption Spectroscopy
An analytical method in which a small quantity of a sample is introduced into a flame. The absorption spectra are characteristic of some materials present, for example metals.
AW
Antiwear. Denotes the presence of an antiwear additive in an oil to minimize wear.
Consistency
General term: viscosity in oils; penetration in greases.
Emission spectroscopy
An analytical method in which a small quantity of a sample is “sparked.” The spectrum of light emitted is characteristic of some materials present, for example, metals present as elements.
Ester
Reaction product between an organic acid and an alcohol [RC(O)OR].
Ferrography
An analytical method whereby magnetic material, for example iron and chromium, under the influence of a magnetic field, are isolated and studied optically. Yields information on large as well as small particles and their possible source.
FTIR
Fourier Transform Infrared Spectroscopy.
B-1
EPRI Licensed Material Appendix B
Grade, Penetration
Standard NLGI grease consistency classes (grade definitions) are as follows: NLGI Grade No.
ASTM (D 217) Penetration, 60 Stroke, Worked, 25° C (77°F), 0.1 mm
000
445-475
00
400-430
0
355-385
1
310-340
2
265-295
3
220-250
4
175-205
5
130-160
6
85-115
Grade, Viscosity
Standard viscosity classifications by ISO. Grades are matched to centistoke viscosities at 40°C (104°F); for example, 32 grade is about 32 cSt at 40°C. Grades range from 2 to 1500.
HD
Heavy Duty. HD oils are extra inhibited with antioxidation and antiwear additives to withstand unusually high stresses.
Highly Refined Mineral Oil
Refined to the point that all or most of the naturally occurring inhibitors or impurities are removed, for example, a white oil or a near white oil, also hydrorefined or hydrocracked oils.
Hydrolysis
Interaction with water.
Infrared (IR)
An analytical method whereby infrared light is passed through, or bounced off, a sample. Many organic substances have characteristic absorbencies at specific wavelengths.
Inhibitor
A chemical naturally present or added to lubricants to enhance or to suppress certain properties or characteristics.
ISO
International Standards Organization.
Lubricant
A material, usually an oil or a grease, designed to reduce friction and wear between moving machine elements, acts as an hydraulic medium to remove heat, and so on.
Molysulfide
A laminar solid powder of sulfides of molybdenum added to lubricants to enhance antiscuff performance.
B-2
EPRI Licensed Material Appendix B NL
Non-lead. In most gear lubricants lead has been displaced by other additives.
NLGI
National Lubricating Grease Institute.
OEM
Original Equipment Manufacturer.
Penetration (ASTM D 217; D 1403)
In a grease, the depth of entry in 1/10 millimeters of a dropped standard cone into a grease sample. A measure of consistency (the higher the penetration, the lower consistency of the grease).
Pyrolysis
Interaction with heat.
R&O
Rust and oxidation-inhibited.
Radiolysis
Treatment with radiation; interaction with radiation.
Viscosity
Property of a fluid or semi-fluid that offers continuous resistance to flow. Usually measured as the time of flow through a calibrated orifice, expressed as centistokes (cSt, mm²/sec.). Other means of expression are also used. The interrelationships of these are shown in Table B-1.
Worked Penetration (ASTM D 217; D 1403); Working
Penetration (or consistency) of a grease measured after a number of double strokes, for example 60 in a standard apparatus that provides shear. 60 10,000 and so on. Expressed as P , P
B-3
EPRI Licensed Material Appendix B Table B-1 Viscosity Equivalents
B-4
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